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Atom

The atom is the smallest unit of matter. Every atom contains one nucleus at least one electron.

The nucleus contains at least one positively charged proton and an equal number of neutrally

charged neutrons. Every atom also has at least one negatively charged electron bound to the

nucleus. When the number of protons (the atomic number) is equal to the number of electrons,

the atom is neutral. When the number of protons and number of electrons differ, the result is an

ion.

The way electrons are distributed around an atom or molecule is known as an electron

configuration. Electrons are distributed among “shells” which may be thought of as energy

levels. The configuration that corresponds to the lowest energy level is called ground state.

Every other configuration is considered an excited state. Electrons always fill the lower energy

levels first.

To write an electron configuration:

• Locate the atomic number

• If the atom being studied is charged, this should be taken into account. Cations

(positively charged) will have fewer electrons in the magnitude of the charge. Anions

(negatively charged) will have extra electrons in the magnitude of the charge.

• Understand the order of orbitals:

o S – 1 single orbital, holds 2 electrons

o P – 3 orbitals, holds 6 electrons

o D – 5 orbitals, holds 10 electrons

o F – 7 orbitals, holds 14 electrons

• Fill the orbitals in the following order, according to the number of electrons of the atom

being studied.

o 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s.

• The number of electrons is written in superscript to the right of the orbital letter. For example, the configuration for neutral neon would be written as 1s2 2s2 2p6

.

Periodic Table

The periodic table contains the most important information about all known elements. An

element is a substance that is composed purely from one type of atom.

The periodic table is broken into four main groups.

• Main group elements: active metals in columns (also called groups) 1 and 2 as

well as the metals, semimetals and nonmetals in columns 13-18.

• Transition metals: the elements that serve as a transition between the two main

groups

• Lanthanides and Actinides: known as the inner transition metals because their

atomic numbers are actually located between the first and second elements in

the last two rows (also called periods) of transition metals.

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Electronegativity is an important concept in chemistry and can be charted predictably across the

periodic table. Electronegativity is an atom’s measure of attraction for electrons.

• Electronegativity increases from bottom to top within groups

• Electronegativity increases from left to right across periods

Additional important information about each element can be gathered from the periodic table:

• The number of protons in an atom will always determine what element it is from. The number of protons will always be the same for all atoms from the same element. The number of protons is called the atomic number.

• The number of electrons, in a neutral atom, is equal to the number of protons. If the atom is an ion, the number of electrons will vary.

• The number of neutrons in an atom can also vary. If an atom has a different number of neutrons, it is called an isotope.

• The mass number is equal to the number of protons plus the number of neutrons. In order to calculate the number of neutrons, subtract the atomic mass minus the atomic number.

• The relative atomic mass, also called the atomic weight, is an average of the atomic masses of all the different isotopes in a sample.

Example:

Hydrogen’s chemical symbol is H. Its atomic number is 1 and atomic weight is

1.00794. This shows that there are some isotopes of hydrogen. A neutral

hydrogen atom would have a mass of 1.

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Atomic Number

Each element has its own atomic number, which is based on the number of protons in an atom. The

number of protons will always remain the same for an element. In a neutral atom, the number of protons

is equal to the number of electrons. The number of electrons can change based on various reactions that

can occur involving them.

Example: All atoms with 2 protons are Helium.

Subatomic particles

An individual unit of an element is called an atom. Atoms cannot be broken into smaller pieces while still

maintaining the properties of that element. Atoms get their properties from their subatomic particles.

Atoms consist of two regions: the nucleus and

the electron cloud. The nucleus is in the

center of the atom and contains positively

charged protons and uncharged neutrons.

This is what makes up the mass of the atom.

The electron cloud is a much larger region of

the atom; however, the mass is negligible.

This region is where electrons are found.

Electrons are negatively charged. It is the

attraction between the positively charged

protons and the negatively charged electrons

that holds the atom together.

Most atoms have all three of these subatomic

particles, except hydrogen, which doesn’t

have any neutrons.

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Chemical Formulas

Understanding chemical formulas and how to read them is important. It is the basis for understanding

reactions. Consider the equation below:

The elements and molecules shown on the left are the reactants. These are the substances used to begin

a chemical reaction. After the reaction takes place, it forms products. These are shown on the right side

of the equation. The arrow between the two shows that a reaction took place. It always points from the

reactants to the products.

There is a “(g)” listed after each molecule. This tells the state of matter of the molecule. In this case, all of

the molecules are in a gaseous state. It could be a liquid (l), solid (s) or gas (g). Sometimes it will say

(aq), which means aqueous. This means that those molecules have been dissolved in water.

There is a subscript of 2 with each of the reactants. Subscript means written slightly lower than the rest of

the text. A subscript number tells how many atoms of an element are present. In this specific reaction, it

takes 2 hydrogen atoms to combine with 2 chlorine atoms. The regular sized 2 in the products is called a

coefficient. This refers to how many of an entire molecule there are. In this case, there are 2 HCl

molecules made in the reaction.

Below are several images to help understand the terms and what they may look like:

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Molecular Weight

The sum of the weight of all the atoms in a given formula equals the molecular weight of the

substance. Atoms are measured in atomic mass units (amu).

Calculating the molecular weight is important because it is necessary information to determine

how many grams are in one mole of a substance. The mole is a unit of measure in chemistry

which denotes the quantity of a substance present.

To calculate molecular weight:

• Determine the number of atoms of each element are present in a substance

• Multiply the atomic weight of each element by respective the number of atoms of

each element

• Add them

Stoichiometry (Molar Mass)

Molar mass is the standard unit in chemistry. It shows how many grams of a substance are

present within 1 mole of that substance. The units for mole are grams/mole.

To find the molar mass of a compound:

• Determine the quantity of each atom type within the compound - this information is found

in the chemical formula

• Multiply (number of atoms present)(atomic weight of atom)

• Add them and include units

Conversions are another important part of stoichiometry. When given a quantity (in either grams

or moles) as well as a chemical formula (to solve for the molecular weight), there is enough

information to solve for an unknown using the formula:

�� ℎ� ��

�� ℎ� �� =

�� ℎ� ��

1 ��

Density

Density is a characteristic property of a

substance. It is a relationship between the mass

of the substance and how much space it takes

up. The mass of atoms, their size and how they

are arranged determine the density of a

substance. Objects with the same volume but

different masses will have different densities.

Density can be calculated by using the formula

� = ��⁄

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Solids can be suspended in liquids based on their densities. The figure shows a representation of various

solids and liquids that naturally separate into layers based on their densities.

Description of Matter

Matter is anything that occupies space and has mass. All matter is made up of substances called

elements, which have specific chemical and physical properties. Elements cannot be broken down into

other substances.

Matter exists in three phases: solid, liquid or gas.

Water, Hydrogen Bonding, and Polarity of Substances

When electron density is distributed unevenly, a molecule is said to be polar. Using the water molecule

(see picture, page 5) as an example, note the following:

• Each hydrogen atom is covalently bonded to the oxygen atom. This means there is a shared pair

of electrons within each bond.

• Oxygen also has two unshared pairs of electrons – this means that oxygen is more

electronegative with respect to hydrogen.

• Water is polar. There is a partial negative charge near the oxygen atom and partial positive

charges near the hydrogen atoms.

• Water has hydrogen bonds. The electrostatic attraction between the hydrogen atoms and the

oxygen atom give water unique characteristics such as its ability to be a solvent for ions and other

molecules (ions and other molecules can dissolve into water), have a strong surface tension,

have a high specific heat and high heat of vaporization, and have a hydrophobic effect towards

nonpolar compounds.

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Dissociation

Dissociation is a process in which molecules or ionic compounds separate into smaller particles such as

atoms or ions. This process is reversible. For example, it is through this process that lead sulfate can be

separated into a lead ion and a sulfate ion. This process can be undone if those ions were to bond

together again.

Based on the example below, the reaction begins with PbSO4. This is dissociated, or separated into two

ions, Pb2+ and SO42-. The products of this reaction are parts of the reactant.

Emulsion

An emulsion is a colloid of two or more immiscible (not forming a homogeneous mixture when combined)

liquids where one liquid contains a dispersion of the other liquid. A common example of an emulsion is oil

and water mixtures. When shaken together, the oil will form drops and disperse throughout the water.

Colloids are substances with another solid, liquid or gas substance suspended within them. An example

would be a gel.

pH

pH is a measure of the concentration of hydrogen ions (H+) versus

hydroxyl ions (OH-) in a solution. Adding an acid to a solution

releases hydrogen ions. Adding a base releases hydroxyl ions.

Acids and bases are chemical opposites. If a base is added to an

acidic solution, the solution becomes less acidic and moves

towards the middle of the pH scale. This is called neutralizing the

acid. If an acid is added to a basic solution, the solution becomes

less basic and moves toward the middle of the pH scale. This is

called neutralizing the base.

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Conjugate Acids and Bases

Conjugate acids and bases have one very important characteristic – they lose or gain protons

equally. The reaction can be characterized as:

�� → ��

As described above, the conjugate pairs are “Acid and Conjugate Base” and “Base and

Conjugate Acid.” Also important to identify conjugate pairs is to realize the stronger the acid

reactant, the weaker its conjugate base; the stronger the base reactant, the weaker its

conjugate acid. The opposite is also true (the weaker the acid reactant, the stronger its

conjugate base; the weaker the base reactant, the stronger its conjugate acid).

To identify conjugate pairs:

• Identify the conjugate acid – look for the pair of compounds which are related. The

conjugate acid will have gained a hydrogen ion whereas the base reactant will contain

one less hydrogen ion. The conjugate base will have lost one hydrogen ion whereas the

acid reactant will contain one more hydrogen ion.

The below table contains examples of common acids and their conjugate bases.

Acid Conjugate Base

H2F+ HF

HCl Cl−

H2SO4 HSO−4 HNO3 NO−3 H3O+ H2O HSO−4 SO2−4 H3PO4 H2PO−4 CH3COOH CH3COO− H2CO3 HCO−3 H2S HS− H2PO−4 HPO2−4

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NH+4 NH3 HCO−3 CO2−3 HPO2−4 PO3−4 H2O OH−

Buffers: Carbonic acid

Conjugate acids and bases are involved in buffering systems. Buffers are solutions that can resist

changes in pH. These are key to maintaining stable H+ ion concentrations. When there are too many H+

ions, a buffer will help to absorb some of them, which will bring the pH back up. When there are too few, a

buffer will donate some of its own H+ ions to reduce the pH. Buffers typically consist of an acid-base pair.

Carbonic acid (H2CO3) is a buffer that maintains the pH of human blood. The base that it pairs up with is

the bicarbonate ion (HCO3-). It is formed when carbon dioxide enters the bloodstream and combines with

water. It is the main form in which carbon dioxide travels in the blood between muscles, where it is made,

and the lungs, where it is converted and released as waste.

Organic Chemistry

Carbon can form covalent bonds with itself and other

elements to create a wide variety of structures.

Carbon is known as the building block of life.

Compounds and molecules containing carbon are

considered organic, except oxides, carbonates,

carbides ad cyanides. If a compound doesn’t contain

any carbon atoms, it is not an organic molecule.

Carbon can bond to itself and create a ring-like

structure. From there, functional groups can attach to

the compound. Organic compounds and molecules

can become very large.

Chemical Bonding

Chemical bonding is the joining of atoms to form new substances. The properties of the new substances

are different than the properties of the elements. Electrons are either gained, shared or lost in a bond. Not

all of the electrons in an atom are capable of bonding, rather only the valence electrons. The valence

electrons are the electrons found in the outermost shell of an atom. Most elements are capable of

bonding, and some are more reactive than other, but noble gases rarely form chemical bonds since their

outer shell is full.

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Hydrogen bonds are weak interactions that form between a hydrogen with a partial positive charge and

a more electronegative atom, such as oxygen. The hydrogen atoms involved in hydrogen bonding must

be attached to electronegative atoms, such as oxygen, nitrogen or fluorine.

Ionic bonds form when electrons are transferred from one atom to another atom. They form so that the

outer shells of the atoms involved are full. This happens between a metal and a non-metal.

Transferring electrons changes the charge of the atoms involved, causing

them to become ions. If atoms lose electrons, they are losing a negative

particle, which results in a positive charge since there are more protons now

than electrons in the atom. If an atom gains an electron, it becomes

negatively charged since it is gaining a negative particle and therefore has

more electrons than protons.

Ionic compounds are typically neutral, despite the individual atoms having a charge since the charges

typically cancel each other out. Ionically bonded compounds form a crystal lattice structure.

Covalent bonds form when atoms share one or more pairs of

electrons. Two nonmetals can bond in this way. This type of bond is

very common with organic molecules.

Protein Linkage

Amino acids are small units that, when

combined, form proteins. They attach to

each other through peptide bonds. An

amino acid contains a carboxylic group

and an amino group. There are 20

common amino acids, which are

classified based on their R group.

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Peptide bonds are covalent bonds formed by a reaction

between the carboxylic group of one amino acid and

the amino group of another amino acid. This reaction

releases a molecule of water as the byproduct.

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DNA, RNA, and their roles

DNA (deoxyribonucleic acid) is

a double helix made up of

nucleotides. A nucleotide is

made up of a sugar

(deoxyribose), a phosphate

group, and one of four

nitrogenous bases: adenine

(A), thymine (T), guanine (G),

or cytosine (C). C and T are

called pyrimidines, and have

just one ring, whereas A and G

have two rings and are called

purines.

DNA nucleotides assemble

and form covalent bonds. DNA

nucleotides join in very specific

ways. They always pair in this

way: A and T, C and G. This is

called complementary base

pairing. Because of their shape and properties, they can only form bonds in this way. The role of DNA is

for long term storage of genetic information.

RNA (ribonucleic acid) carries out

instructions found in DNA and is

used for protein (peptide) synthesis.

It can be found in three different

forms. Messenger RNA (mRNA)

carries the genetic information

copied from DNA in the form of

codons, or three-base code

segments. Transfer RNA (tRNA)

deciphers the code in the mRNA.

Ribosomal RNA (rRNA) matches the

correct protein to the code. One

difference between DNA and RNA is

that RNA has one different

nucleotide. Both have adenine,

cytosine and guanine, but RNA has

a fourth base called uracil (U), in

place of thymine.

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Reactions

1. Synthesis reaction: Reaction in which two or more substances combine to form one new

compound.

Synthesis of two elements: C + O2 → CO2

Synthesis of two compounds: 2CaO + 2H2O → 2Ca(OH)2

Synthesis of a compound and an element: 2CO + O2 → 2CO2

2. Decomposition reaction: A reaction in which a single compound breaks down to form two or

more simpler substances.

3. Single replacement reaction: A reaction in which one element or radical takes the place of

another element or radical in a compound.

4. Double replacement reaction: A reaction in which a gas, a solid precipitate, or a molecular

compound forms from the exchange of ions between two compounds.

5. Neutralization reaction: a special type of double replacement reaction where an acid reacts with

a base to produce an ionic salt and water.

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6. Combustion reaction: a reaction of a fuel with

oxygen, producing energy in the form of light

and/or heat. Complete combustion occurs

when a sufficient amount of oxygen is present.

All of the carbon and hydrogen atoms react to

form water and carbon dioxide.

CxHy + O2 → H2O + CO2

CH4 + O2 → H2O + CO2

C5H12 + O2 → H2O + CO2

7. Redox reaction**: this reaction gets its name from its type of reaction: oxidation – reduction. For a

reaction to be considered a redox reaction, a transfer of electrons must occur.

There are two ways to demonstrate that a reaction is a redox reaction:

• Solve for oxidation numbers and compare them between reactants and products. This method is

very complex – an addendum detailing this method has been attached to the end of this section

for optional review

• Rewrite the reaction into “half reactions” with electrons included. This method is explained below.

In a redox reaction, the compound that loses electrons is the compound that is oxidized. The compound

that gains elections is the compound that is reduced. Below shows the half reaction versions of the

oxidation of copper metal and the reduction of silver ions.

Cu(s) → Cu2+(aq) + 2e- Copper metal loses electrons, is oxidized

Ag+(aq) + e- → Ag(s) Silver ion gains electrons, is reduced.

Next the half reactions need to be combined and balanced. The top reaction has 2 electrons and the

bottom has 1. Multiplying the bottom half reaction by two and combining them forms a balanced redox

reaction.

Cu(s) + 2 Ag+(aq) → Cu2+

(aq) + 2 Ag(s)

Gas Laws

Boyle’s Law: when studying gases, pressure and volume are inversely proportional. This means as

pressure increase, volume decreases; as pressure decreases, volume increases.

Charles’s Law: when studying gasses, temperature and volume are directly proportional. This means as

temperature increases, volume increases; as temperature decreases, volume decreases.

Avogadro’s Law: when studying gases, volume and number of moles of gas are directly proportional. This

means that at a constant temperature and pressure, the volume of gas increases as the number of moles

increase.

Combined Gas Law: when the above three laws are combined, a helpful formula emerges:

�� !" = �" "!�

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Ideal Gas Law: when studying gasses, this law is used to predict the behavior of gas under many

conditions

#$ = %&'

Where:

P= pressure (atm)

V= volume (L)

n= number of moles

R= Avogadro’s constant 6.02214086 × 1023 mol-1

*note the Gas Constant, 0.0821 L·atm/mol·K is used when pressure is measured in atm

T= temperature in K (Celsius + 273)

Specific Heat

Specific heat is the amount of heat (energy) required to raise 1 gram of substance by 1 degree Celsius.

Substances have a specific heat capacity, which can be solved for using the below equation.

� =(

�∆!

Where:

s= specific heat capacity

q= heat

m= mass

∆T= change in temperature

Specific heat is usually measured by the unit *

+°-

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Volume-density displacement

Density: � = ��⁄

Volume (rectangular prism) = . / 0 / 1

Units for mass could be: g, kg, mg

Units for volume will be cubed unit of length

Example:

A carver begins work on the following block of granite that weighs 2700 g. What is the density of the

granite?

How to solve:

Formula: � = ��⁄ Solving for: Density

m = 2700 g v = 10 x 5 x 20 = 1000 cm³

D = m/v D = 2700g/1000cm³ D = 2.7 g/cm³

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**Addendum: Redox Reaction Oxidation Number Method (in depth)

Redox reaction: this reaction gets its name from its type of reaction: oxidation – reduction. All redox

reactions involve the transfer of electrons. This can be proven by observing a change in oxidation number

between products and reactants.

The below are rules for determining oxidation number:

• Free elements always have an oxidation number of 0.

• Monoatomic ions always have oxidation numbers equal to the charge of the ion.

• Hydrogen’s oxidation number is +1 unless it is combined with less electronegative

elements, in which case the oxidation number of H is -1.

• In compounds, oxygen has an oxidation number of -2, with the exception being that it is

-1 when in peroxides.

• Group 1 elements have an oxidation number of +1

• Group 2 elements have an oxidation number of +2

• Group 17 elements in binary compounds have an oxidation number of -1

• The sum of oxidation numbers of all of the atoms in a neutral compound must equal 0.

• The sum of oxidation numbers in a polyatomic ion must equal to the charge of the ion.

To prove that a reaction is a redox reaction, the transfer of electrons must occur. This can be shown by

demonstrating differing oxidation numbers between reactants and products.

2�"�3 � 3� → 4� � 3��"

Reactant Oxidation number Product Oxidation number

�" +3 � 0

�3 -2 � +4

� 0 �" -2

To recognize which element is being oxidized, look for an increase in oxidation number – this

shows that the element is losing electrons. In the above example, C was oxidized (0, +4).

To recognize which element is being reduced, look for a decrease in oxidation number – this

shows that the element is gaining electrons. In the above example, A was reduced (+3, 0).

To recognize the reducing agent, find the reactant that is being oxidized, which causes something

else to be reduced. In the above example, C was the reducing agent.

To recognize the oxidizing agent, find the reactant that is being reduced, which causes something

else to be oxidized. In the above example, A was the reducing agent.

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Periodic Table and Atoms Practice Worksheet

1. Draw an atom with 5 protons, 6 neutrons and 5 electrons. Label each with its respective charge.

2. Label the following parts of a periodic table square:

3. What does the atomic number represent?

4. What does the atomic mass represent?

5. How would you figure out the number of neutrons in an atom?

6. Fill in the blanks to complete the table.

Element

Name Symbol

Atomic

Number

Atomic

Mass

(rounded)

# of

Protons

# of

Electrons

# of

Neutrons

Ar

4

5

calcium

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Chemical Formulas and Reactions Practice Worksheet

1. Zn(NO3)2

Total

Element symbol

# atoms present

2. What is the small 2 called in the formula above? _________________

3. 4H2O

Total

Element symbol

# atoms present

4. What is the large 4 called in the formula above? ______________

5. Label the following reactions as either: synthesis, decomposition, single replacement, double

replacement. Then underline the reactants and circle the products.

2CO � O" → 2CO"

4Fe � 3O" → 2Fe"O3

2H"O" → 2H"O � O"

2KBr � Cl" → 2KCl � Br"

C6H6 � Cl2 → C6H5Cl � HCl

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Chemistry in the Body Practice Worksheet

Answer the following questions relating to Carbonic acid:

1. Who has it in their body?

2. What is it?

3. When will it work?

4. Where is it found in the body?

5. Why is it present?

6. What element must be present in order for a molecule to be considered organic?

_____________________

7. The letters “DNA” stand for _____________________________________.

8. DNA is composed of smaller subunits known as ________________________.

9. The four nitrogen bases that are found in DNA are ___________________,

__________________, ____________________ and ____________________.

10. DNA looks like a ladder twisted into a shape known as a ___________________.

11. Which nitrogen bases always pair with one another? _______________________.

There are three kinds of RNA. ______________________ carries the information from the nucleus to the

ribosomes in the cytoplasm. ____________________ reads the message and binds to the specific

_____________________ to make the protein. ___________________ is the most abundant form of

RNA and makes up ribosomes.

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Chemical Bonds Practice Worksheet

Ionic Bond between a Metal and Nonmetal (M + NM)

Covalent Bond between a Nonmetal and Nonmetal (NM + NM)

Metallic Bond between a Metal and Metal (M+ M)

Determine if the elements in the following compounds are metals or nonmetals. Describe the type of

bonding that occurs in the compound.

Compound Element 1

(metal or nonmetal?)

Element 2

(metal or nonmetal?) Bond Type

NO2 N = non-metal O = non-metal Covalent

NaCl

SO2

MgBr2

CaO

H2O

K2O

O2

CuCl2

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Chemistry Basics and Processes Practice Worksheet

Use the word bank below to fill up the blanks.

Word Bank: gases, particles, move, shape, solid, runny, tiny, gas, solid, invisible around, level, container

Every material is made up of lots of ______________ particles. All materials are either a solid, liquid or

_____________. In a ____________ all particles are packed tightly together and can hardly move. Some

solid stays in its own _____________ unless we cut it of shape it ourselves.

Anything you can take hold of is a _________________. The __________________ in a liquid are not so

tightly packed. They can ________ a little. Liquids are _____________ and flow downwards. They may

take the shape of the __________________ they are in. The surface of a liquid stays

___________________.

The particles in _______________ have lots of room and move around all over the place, all the time.

Gases are all ______________ us spreading into any empty space they can.

1. A student finds a rock on the way to school. In the laboratory, he determines that the volume of the

rock is 22.7 mL, and the mass in 39.943 g. What is the density of the rock?

2. The density of silver is 10.49 g/cm3. If a sample of pure silver has a volume of 12.993 cm3, what

would the mass?

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ANSWER KEY: Periodic Table and Atoms

1. Draw an atom with 5 protons, 6 neutrons and 5 electrons. Label each with its respective charge.

2. Label the following parts of a periodic table square:

3. What does the atomic number represent?

Number of protons (also number of electrons in a neutral atom)

4. What does the atomic mass represent?

Protons + neutrons

5. How would you figure out the number of neutrons in an atom?

Atomic mass - atomic number = neutrons

6.

Element

Name Symbol

Atomic

Number

Atomic

Mass

# of

Protons

# of

Electrons

# of

Neutrons

Argon Ar 18 40 18 18 22

Beryllium Be 4 9 4 4 5

Boron B 5 11 5 5 6

Calcium Ca 20 40 20 20 20

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ANSWER KEY: Chemical Formulas and Reactions

1. Zn(NO3)2

Total

Element symbol Zn N O 3

# atoms present 1 2 6 9

2. What is the small 2 called in the formula above? subscript

3. 4H2O

Total

Element symbol H O 2

# atoms present 8 4 12

4. What is the large 4 called in the formula above? coefficient

5. Label the following reactions as either: synthesis, decomposition, single replacement, double

replacement. Then underline the reactants and circle the products.

2CO � O" → 2CO" Synthesis

4Fe � 3O" → 2Fe"O3 Synthesis

2H"O" → 2H"O � O" Decomposition

2KBr � Cl" → 2KCl � Br" Single replacement

C6H6 � Cl2 → C6H5Cl � HCl Double replacement

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ANSWER KEY: Chemistry in the Body

Answer the following questions relating to Carbonic acid:

1. Who has it in their body? Humans

2. What is it? Buffer

3. When will it work? When paired with bicarbonate

4. Where is it found in the body? Blood

5. Why is it present? It is the main form that carbon dioxide uses to travel in the body

6. What element must be present in order for a molecule to be considered organic? ___Carbon___

7. The letters “DNA” stand for ___deoxyribonucleic acid___

8. DNA is composed of smaller subunits known as ___nucleotides___

9. The four nitrogen bases that are found in DNA are __adenine__, __thymine__, __cytosine__,

and __guanine__

10. DNA looks like a ladder twisted into a shape known as a __double helix__

11. Which nitrogen bases always pair with one another? ___guanine with cytosine, adenine with

thymine___

There are three kinds of RNA. __mRNA__ carries the information from the nucleus to the ribosomes in

the cytoplasm. __tRNA__ reads the message and binds to the specific __codon__ to make the protein.

__rRNA__ is the most abundant form of RNA and makes up ribosomes.

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ANSWER KEY: Chemical Bonds

Compound Element 1

(metal or nonmetal?)

Element 2

(metal or nonmetal?) Bond Type

NO2 N = non-metal O = non-metal Covalent

NaCl Na = metal Cl = non-metal Ionic

SO2 S = non-metal O = non-metal Covalent

MgBr2 Mg = metal Br = non-metal Ionic

CaO Ca = metal O = non-metal Ionic

H2O H = non-metal O = non-metal Covalent

K2O K = metal O = non-metal Ionic

O2 O = non-metal O = non-metal Covalent

CuCl2 Cu = metal Cl = non-metal Ionic

Ready For The HESI


ANSWER KEY: Chemistry Basics and Processes

Every material is made up of lots of __tiny__ particles. All materials are either a solid, liquid or __gas__.

In a __solid__ all particles are packed tightly together and can hardly move. Some solid stays in its own

__shape__ unless we cut it of shape it ourselves.

Anything you can take hold of is a __solid__. The __particles__ in a liquid are not so tightly packed.

They can __move__ a little. Liquids are __runny__ and flow downwards. They may take the shape of the

__container__ they are in. The surface of a liquid stays __level__.

The particles in __gases__ have lots of room and move around all over the place, all the time. Gases are

all __invisible around__ us spreading into any empty space they can.

1. A student finds a rock on the way to school. In the laboratory, he determines that the volume of the

rock is 22.7 mL, and the mass in 39.943 g. What is the density of the rock?

Density = Mass/Volume = 39.943 g/22.7 mL = 1.76 g/mL

2. The density of silver is 10.49 g/cm3. If a sample of pure silver has a volume of 12.993 cm3, what

would the mass?

Mass = Density x Volume = 10.49 g/cm3 x 12.993 cm3 = 136.3 g

Ready For The HESI


HESI A2 Chemistry Practice Test Questions

1. A mystery element has 6 protons, 6 electrons and 6 neutrons. What is its atomic number?

a. 6

b. 12

c. 18

d. Not enough information

2. A mystery element has 13 protons, 13 electrons and 14 neutrons. What element is it?

a. Fe

b. Zr

c. Al


3. What are buffers?

a. Proteins

b. Solutions that resist changes in pH

c. Catalysts in a reaction

d. Inhibitors in a reaction

4. What does carbonic acid do within the human body?

a. Digests food

b. Kills viruses

c. Maintains pH of blood

d. None of the above

Use the following chemical reaction to answer the following questions:

5. What are the reactants?

a. CH4 and O2

b. CO2 and H2O

c. Both

d. None of the Above

6. What are the products?

a. CH4 and O2

b. CO2 and H2O

c. Both

d. None of the Above

7. How many hydrogen atoms are present in the reactants?

a. 2

b. 4

c. 1


Ready For The HESI


8. How many oxygen atoms are in 2O2?

a. 2

b. 4

c. 1

d. 0

9. How many water molecules are present in the products?

a. 2

b. 4

c. 1

d. 0

10. Which of the following is most true?

a. 2H2O has 2 hydrogen atoms total

b. 2 H2O is two water molecules

c. H2O2 is two water molecules


11. Which of the following is most dense?

a. A block of gold that is 12g and 4.6cm³

b. A cube that is 6g and 0.91cm³

c. A block that is 143g and 24.3cm³


12. Solids will always sink in liquids.

a. True, a solid is hard and liquids are not

b. True, solids are heavier than liquids

c. False, solids have a smooth surface so they will float

d. False, it depends on the density of the solid and liquid

13. Which of the following has the most molecular interactions?

a. Solid

b. Liquid

c. Gas


14. Which of the following has the most molecular motions?

a. Solid

b. Liquid

c. Gas


15. Which of the following is most commonly present at very high temperatures?

a. Solid

b. Liquid

c. Gas


Ready For The HESI


16. Which of the following is false about dissociation?

a. It is reversible

b. Ions are not present

c. It involves molecules separating

d. All are true statements.

17. What is present in an emulsion?

a. Water and salt

b. Two or more immiscible liquids

c. Any liquids

d. All are present in emulsion.

18. What is pH?

a. The measure of concentration of H+ and OH-

b. The measure of concentration of hydrogen

c. The measure of concentration of H2O


19. Which of the following is the general reaction for neutralizing acids and bases?

a. Acid + water → base + salt

b. Base + water → acid + salt

c. Salt + water → acid + base

d. Acid + base → water + salt

20. Which of the following is not an organic compound?

a. H2O

b. C2H6

c. C6H12O6


21. Which of the following must be present in order to be considered an organic molecule?

a. H

b. O

c. N

d. C

22. An atom of oxygen has more electrons than a neutral oxygen atom. What is this called?

a. Isotope

b. Ion

c. Both are correct


23. An atom of carbon has less neutrons than a neutral carbon atom. What is this called?

a. Isotope

b. Ion

c. Both are correct


Ready For The HESI


24. An atom has a mass of 16 and 6 protons. What element is it and how many neutrons are there?

a. Sulfur, 10

b. Sulfur, 22

c. Carbon, 10

d. Carbon, 22

.

25. What subatomic particle can always be used to identify an atom?

a. Protons

b. Neutrons

c. Electrons


26. What is the building block of proteins?

a. Lipids

b. Amino acids

c. DNA

d. Cells

27. What differentiates the 20 common amino acids?

a. Color

b. Size

c. R group


28. Which type of bond shares pairs of electrons?

a. Ionic

b. Covalent

c. Both


29. Which type of bond involves atoms gaining or losing electrons?

a. Ionic

b. Covalent

c. Both


30. An atom has a positive charge. What happened to it?

a. Gained an electron

b. Lost an electron

c. Gained a proton

d. Lost a proton

31. An atom has a negative charge. What happened to it?


b. Lost an electron

c. Gained a proton

d. Lost a proton

Ready For The HESI


32. DNA bases include all but which of the following?

a. Adenine

b. Thymine

c. Uracil

d. Cytosine

33. RNA bases include all but which of the following?

a. Adenine

b. Thymine

c. Uracil

d. Cytosine

34. Which type of RNA is used to carry genetic code copied from DNA?

a. mRNA

b. tRNA

c. rRNA


35. When propane is reacted in the presence of oxygen gas, the products of this combustion reaction

are:

a. C + H2

b. CH2 + H2O

c. CO2 + H2

d. CO2 + H2O

36. Which of the following are decomposition reactions?

1) CH4 (g) + O2 (g) → CO2 (g) + H2O (l)

2) CaO (s) + CO2 (g) → CaCO3 (s)

3) Mg (s) + O2 (g) → MgO (s)

4) PbCO3 (s) → PbO (s) + CO2 (g)

a. 2 and 3

b. 2, 3, 4

c. 4

d. All are decomposition reactions

37. The products of a reaction are CO2 + H2O. Which type of reaction is this most likely to be?

a. Synthesis

b. Decomposition

c. Single replacement

d. Combustion

Ready For The HESI


38. The chemical equation, KClO3 → KCl + O2, is an example of which type of reaction?

a. Single replacement

b. Double replacement

c. Combustion

d. Decomposition

39. Combination reactions always:

a. Use only one reactant

b. Involve an element and an ionic compound

c. Form only one product

d. Require oxygen gas

40. In a double replacement reaction:

a. Energy in the form of heat or light is often produced

b. The reactants are usually a metal and a nonmetal

c. A gas, solid precipitate or compound forms in the exchange of ions

d. All statements are true.

41. The chemical equation, Cr + Fe(NO3)2 → Fe + Cr(NO3)3, is an example of which type of reaction?


b. Decomposition

c. Double replacement

d. Combustion

42. This region of the atom holds the protons.

a. Nucleus

b. Orbitals

c. Electron cloud


43. Which subatomic particle does not contribute to an atom’s mass?

a. Proton

b. Neutron

c. Electron

d. All contribute to an atom’s mass.

44. A piece of cork has a volume of 23.5 cm³ and a mass of 5.7g. What is its density?

a. 0.243 g/cm³

b. 4.123 g/cm³

c. 133.95 g/cm³

d. None are correct

Ready For The HESI


45. A student performs an experiment with three unknown fluids and obtains the following

measurements. Choose the correct order of the liquids based on how they would separate in a

beaker, listed from bottom to top.

Fluid A: m = 2060 g, V = 2000 mL Fluid B: m = 672 g, V = 850 mL

Fluid C: m = 990 g, V = 1100 mL

a. A, B, C

b. A, C, B

c. C, A, B

d. B, A, C

46. There is a block on your desk that acts as a paperweight. Its measurements are 3 cm by 4 cm by 6

cm. The block has a mass of 184.32 g. What is its density?

a. 13271.04 g/cm³

b. 2.56 g/cm³

c. 0.39 g/cm³

d. None are correct

47. What is the mass of the ethyl alcohol that exactly fills a 200.0 mL container? The density of ethyl

alcohol is 0.789 g/mL.

a. 157.8 g

b. 253.49 g

c. 0.0039 g

d. None are correct

48. What volume of silver metal will weigh exactly 2500.0 g. The density of silver is 10.5 g/cm³.

a. 26250 cm³

b. 238.1 cm³

c. 0.0042 cm³

d. None are correct

49. A flask that weighs 345.8 g is filled with 225 mL of carbon tetrachloride. The weight of the flask and

carbon tetrachloride is found to be 703.55 g. From this information, calculate the density of carbon

tetrachloride.

a. 1.59 g/mL

b. 2.76 g/mL

c. 1.4 g/mL

d. None are correct

50. 28.5 g of iron shot is added to a graduated cylinder containing 45.5 mL of water. The water level rises

to the 49.1 mL mark, from this information, calculate the density of iron.

a. 0.63 g/mL

b. 7.92 g/mL

c. 0.58 g/mL

d. None are correct

Ready For The HESI


51. Subatomic particles consist of:

a. Isotopes

b. Ions

c. Protons, Neutrons, and Electrons

d. Elements

52. Which of the following is true of elements?

a. They are substances made of 100% of the same type of atom

b. When neutral, they are substances in which the number of protons and electrons are identical

c. The positively charged protons and negatively charged electrons are responsible for the

attraction of atoms within an element

d. All of the above are true

53. Which groups of elements on the periodic table are considered main group elements?

a. Groups 1, 2, 13, 14, 15, 16, 17, and 18

b. Groups 1, 2, 14, 15. 16, 17, and 18

c. Groups 13-18

d. Groups 1-2

54. What are transition metals?

a. Elements that serve as a transition between group 1 and 2 elements.

b. Elements that serve as a transition between the two main group elements

c. Elements that serve as a transition between lanthanides and actinides

d. Elements that have electrons which do not transition between orbitals

55. In which order do electrons fill orbitals?

a. 1, 2, 3, 4

b. a, b, c, d

c. 2, 2, 6, 6

d. s, p, d, f

56. Which of the following is the correct electron configuration of Chlorine?

a. 1�"2�"2AB3�"

b. 1�"2�"2AB3�"3AC

c. 1�"2�"2AB3�"3AB

d. 1�"2�"2AB3�"3AB4�"

57. What applications does molecular weight have in chemistry?

a. It is used to determine how many grams are in one mole of a substance

b. It is used to determine an element’s state of matter

c. It is used to determine electron configuration

d. It is used to determine entropy

58. Determine the molecular weight of the caffeine molecule with formula CDH�ENGO"

a. 182.1906 g/mol

b. 170.1906 g/mol

c. 194.1906 g/mol

d. 206.1906 g/mol

Ready For The HESI


59. Determine the molar mass of table salt NaCl

a. 58.44 g/mol

b. 81.43 g/mol

c. 58.44 amu

d. 81.43 amu

60. Convert 25g KMnO4 to moles

a. .929 mole

b. 2.73 mole

c. .158 mole

d. .169 mole

61. Of the below, which element is most electronegative?

a. K

b. Fe

c. Cl

d. Ne

62. What characteristic is true for polar substances?

a. Polar substances have low freezing points

b. Polar substances have uneven electron distribution

c. Polar substances are composed of transition metals

d. Polar substances have a high affinity for non polar substances

63. Which of the following properties of water is due to hydrogen bonds within the molecule?

a. Strong surface tension

b. High specific heat

c. High heat of vaporization

d. All of the above

64. Which of the following characteristic are true of conjugate acids and bases?

a. They gain and lose electrons equally

b. They gain and lose protons equally

c. They gain and lose neutrons equally


65. Which of the below is true of conjugate pairs?

a. They may either be “base + conjugate acid” or “acid + conjugate base”

b. They may either be “acid + base” or “conjugate acid + conjugate base”

c. If one member of the pair is very strong, the conjugate member of the pair is usually weak

d. More than one of the above are true

66. How are conjugate pairs identified?

a. The conjugate acid to the reactant base will have lost a hydrogen ion

b. The conjugate acid to the reactant base will have gained a hydrogen ion

c. The conjugate base to the reactant acid will have gained a hydrogen ion


Ready For The HESI


67. How are redox reactions classified?

a. Redox reactions involve the transfer of elections and change of oxidation numbers

b. Redox reactions involve the transfer of hydrogen ions and change of oxidation numbers

c. Redox reactions involve the translocation of conjugate pairs


68. The rules for determining oxidation number are many and complex. Below is a list of the rules – some

of which are TRUE and some of which are FALSE.

1. Free elements always have an oxidation number of 0.

2. Monoatomic ions always have oxidation numbers equal to the charge of the ion.

3. Hydrogen’s oxidation number is +1 unless it is combined with less electronegative


4. In compounds, oxygen has an oxidation number of -2, with the exception being that it is -

1 when in peroxides.

5. Group 1 elements have an oxidation number of 0

6. Group 2 elements have an oxidation number of +1

7. Group 17 elements in binary compounds have an oxidation number of -1

8. The sum of oxidation numbers of all of the atoms in a neutral compound must equal 0. 9. The sum of oxidation numbers in a polyatomic ion must equal to the charge of the ion.

Which are FALSE?

a. 2 and 7

b. 2 and 5

c. 5 and 6

d. 6 and 9

69. Which of the below are redox reactions?

a. 2Fe2O3(s)+3C(s)→4Fe(s)+3CO2(g)

b. NaCl+AgNO3⟶AgCl +NaNO3

c. 3C2H2⟶C6H6

d. HCl+H2O⟶Cl−+H3O+

70. Assign oxidation numbers to each element of this compound: Na2SO4

a. Na=+1, S=+1, O=-2

b. Na=+2, S=-2, O=0

c. Na=0, S=0, O=+2

d. Na=+1, S=+6, O=-2

71. The combined gas law:

a. Is a combination of Boyle’s law, Charles’s law, and Avogadro’s Law

b. Is represented by �� !" = �" "!�

c. Neither are true

d. Both are true

Ready For The HESI


72. A gas has a volume of 23L at 200K and 12 atm. What would the volume of the gas be at 300K and 14

atm?

a. 20L

b. 29.6 L

c. 30.2 L

d. Unable to determine with the information given

73. The ideal gas law

a. Is used to predict the behavior of gas under many conditions

b. Has the formula PV=nRT

c. Uses Avogadro’s constant of 6.02214086 × 1023 mol-1


74. What is the pressure exerted by 4 moles of nitrogen gas contained in a 30 L container at 298K? a. 39, 736 atm b. 2.3927973e+25 atm

c. 3.26 atm d. None of the above

75. Specific heat

a. Is the amount of energy required for a substance to boil b. Is twice the sum of the energy of the chemical bonds within a molecule c. Is generally higher in lanthanides than actinides d. Is the amount of energy required to raise 1 gram of substance by 1 degree Celsius

76. The temperature of an unidentified metal with a mass of 63.4g increased from 25C to 48C as the

metal absorbed 849J of heat. What is the specific heat of this metal?

a. .45 J/gC

b. .55 J/gC

c. .65 J/gC

d. .75 J/gC

Ready For The HESI


Answer Key:

HESI Chemistry Practice Questions and Answers:

1 A mystery element has 6 protons, 6 electrons and 6 neutrons. What is its atomic number?

a. 6

b. 12

c. 18


The correct answer is A. An atom can always be identified based on the number of protons which will

always be the same for atoms of the same element. The atomic number is always equal to the number of

protons.

2. A mystery element has 13 protons, 13 electrons and 14 neutrons. What element is it?

a. Fe

b. Zr

c. Al


The correct answer is C. Atoms can always be identified with the number of protons. Since this atom

has 13 protons, the atomic number is 13, which is aluminum.

3. What are buffers?

a. Proteins

b. Solutions that resist changes in pH

c. Catalysts in a reaction

d. Inhibitors in a reaction

The correct answer is B. Buffers resist change in pH and are key to maintaining stable H+ ion

concentrations.

4. What does carbonic acid do within the human body?

a. Digests food

b. Kills viruses

c. Maintains pH of blood

The correct answer is C. Carbonic acid is a buffer that maintains the pH of human blood. Other acids

are present in the stomach in order to digest food.

Use the following chemical reaction to answer the following questions:

5. What are the reactants?

a. CH4 and O2

b. CO2 and H2O

The correct answer is A. The reactants are always on the left side of a reaction and are the atoms or

molecules present at the start of a reaction.

Ready For The HESI


6. What are the products?

a. CH4 and O2

b. CO2 and H2O

c. Both


The correct answer is B. Products are made by reactions and are always on the right side of the arrow.

7. How many hydrogen atoms are present in the reactants?

a. 2

b. 4

c. 1


The correct answer is B. The subscript 4 after the H symbol indicates that there are 4 atoms of

hydrogen in CH4.

8. How many oxygen atoms are in 2 O2?

a. 2

b. 4

c. 1

d. 0

The correct answer is B. The normal sized 2 is called a coefficient. It means that there are two

molecules of whatever comes after it, in this case there are 2 molecules of O2. O2 has 2 atoms of oxygen

and the coefficient of 2 means that there would be 4 total oxygen atoms. Coefficients are similar to

distributing in algebra. All subscript numbers involved in the compound are multiplied by the coefficient

amount.

9. How many water molecules are present in the products?

a. 2

b. 4

c. 1

d. 0

The correct answer is A. The coefficient of 2 before the water molecule indicates that there are 2 of that

molecule.

10. Which of the following is most true?

a. 2H2O has 2 hydrogen atoms total

b. 2H2O is two water molecules

c. H2O2 is two water molecules


The correct answer is B. The coefficient of 2 means that there are two water molecules. In answer A,

there would be 4 hydrogen atoms since the coefficient would be multiplied by the subscript. In answer C,

there are two hydrogen atoms and two oxygen atoms.

Ready For The HESI


11. Which of the following is most dense?

a. A block of gold that is 12g and 4.6cm3

b. A cube that is 6g and 0.91cm3

c. A block that is 143g and 24.3cm3

The correct answer is B. In order to solve this question, one must find the density of each option and

compare them to find the highest density, which would be the densest. Answer A is 2.61 g/cm3, solved by

12g/4.6cm3. Answer B is 6.59 g/cm3, solved by 6g/0.91cm3. Answer C is 5.88 g/cm3, solved by

143g/24.3cm3.

12. Solids will always sink in liquids.

a. True, a solid is hard and liquids are not

b. True, solids are heavier than liquids

c. False, solids have a smooth surface so they will float

d. False, it depends on the density of the solid and liquid

The correct answer is D. Substances differentiate, sink or float based on their densities. If a solid is

denser than the liquid, it will sink. If the solid is less dense than the liquid, it will float.

13. Which of the following has the most molecular interactions?

a. Solid

b. Liquid

c. Gas


The correct answer is A. Solids are rigid and the atoms are tightly packed together. This means that

there are the most possible molecular interactions.

14. Which of the following has the most molecular motions?

a. Solid

b. Liquid

c. Gas


The correct answer is C. Gas molecules move rapidly due to being at a high temperature. In this state of

matter, the molecules have the most motion compared to the other states.

15. Which of the following is most commonly present at very high temperatures?

a. Solid

b. Liquid

c. Gas

d. None of the above.

The correct answer is C. In order for a substance to change from a liquid to a gas, it requires a large

amount of heat to be added and is typically the state of matter that is present at very high temperatures.

16. Which of the following is false about dissociation?

a. It is reversible

b. Ions are not present

c. It involves molecules separating

The correct answer is B. Dissociation is a reaction where a compound separates into ions. It is

reversible if those ions bond together again.

Ready For The HESI


17. What is present in an emulsion?

a. Water and salt

b. Two or more immiscible liquids

c. Any liquids

d. All are present in emulsion

The correct answer is B. Water and salt combine as a solute and solvent, which, if in the correct

proportions will completely dissolve into one solution. Emulsion must happen with two or more immiscible

liquids. Immiscible liquids do not combine into homogeneous mixtures, meaning that not just any liquids

can make an emulsion.

18. What is pH?

a. The measure of concentration of H3O+

b. The measure of concentration of hydrogen

c. The measure of concentration of H2O


The correct answer is A. pH is a measure of the concentration of H3O+ ions in a solution, not hydrogen

or water.

19. Which of the following is the general reaction for neutralizing acids and bases?

a. Acid + water → base + salt

b. Base + water → acid + salt

c. Salt + water → acid + base

d. Acid + base → water + salt

The correct answer is D. Combining an acid and a base will neutralize them and result in water and a

salt.

20. Which of the following is not an organic compound?

a. H2O

b. C2H6

c. C6H12O6


The correct answer is A. While water is found in nature, it is not an organic compound since it does not

contain carbon.

21. Which of the following must be present in order to be considered an organic molecule?

a. H

b. O

c. N

d. C

The correct answer is D. Carbon must be present in order for a molecule to be considered organic. Most

organic compounds also involve hydrogen, oxygen and nitrogen, but it is not always the case.

Ready For The HESI


22. An atom of oxygen has more electrons than a neutral oxygen atom. What is this called?

a. Isotope

b. Ion

c. Both are correct


The correct answer is B. Ions are atoms that have either gained or lost electrons, and therefore are not

neutral, but have a charge. An isotope is atom of same element with same number of protons but

different number of neutrons.

23. An atom of carbon has less neutrons than a neutral carbon atom. What is this called?

a. Isotope

b. Ion

c. Both are correct


The correct answer is A. Isotopes are atoms that have more or less neutrons than a neutral atom of that

element. This causes the atomic mass to change as well.

24. An atom has a mass of 16 and 6 protons. What element is it and how many neutrons are there?

a. Sulfur, 10

b. Sulfur, 22

c. Carbon, 10

d. Carbon, 22

The correct answer is C. The number of protons is the same as the atomic number, which means this is

carbon. In order to solve for the neutrons, subtract atomic mass minus atomic number.

25. What subatomic particle can always be used to identify an atom?

a. Protons

b. Neutrons

c. Electrons


The correct answer is A. The number of protons in an atom cannot change. If it were to change, it would

not be the same element. The number of protons is equal to the atomic number.

26. What is the building block of proteins?

a. Lipids

b. Amino acids

c. DNA

d. Cells

The correct answer is B. Lipids are a separate type of macromolecule. DNA is made of nucleotides.

Cells are made of organelles and other things. Proteins are made up of various amino acids connected

together in chains or sheets.

Ready For The HESI


27. What differentiates the 20 common amino acids?

a. Color

b. Size

c. R group


The correct answer is C. While amino acids may be color-coded in images and diagrams, this is not how

they are actually differentiated in life. Each amino acid has an R group bonded to it which is unique that

specific molecule.

28. Which type of bond shares pairs of electrons?

a. Ionic

b. Covalent

c. Both


The correct answer is B. Covalent bonds happen between non-metals where electrons are shared so

that each atom has a full valence shell.

29. Which type of bond involves atoms gaining or losing electrons?

a. Ionic

b. Covalent

c. Both


The correct answer is A. Atoms in ionic bonds either gain or lose electrons to have a full outer shell.

30. An atom has a positive charge. What happened to it?


b. Lost an electron

c. Gained a proton

d. Lost a proton

The correct answer is B. Losing an electron is like subtracting a negative. It results in a positive charge

since a negative is removed and there are now more protons than electrons. Protons cannot be gained or

lost.

31. An atom has a negative charge. What happened to it?


b. Lost an electron

c. Gained a proton

d. Lost a proton

The correct answer is A. Gaining an electron, which has a negative charge, will result in an overall

negative charge since there are more electrons than protons. Protons cannot be gained or lost.

32. DNA bases include all but which of the following?

a. Adenine

b. Thymine

c. Uracil

d. Cytosine

The correct answer is C. Uracil is a base found only in RNA.

Ready For The HESI


33. RNA bases include all but which of the following?

a. Adenine

b. Thymine

c. Uracil

d. Cytosine

The correct answer is B. RNA uses uracil in place of thymine. Uracil would pair with adenine.

34. Which type of RNA is used to carry genetic code copied from DNA?

a. mRNA

b. tRNA

c. rRNA


The correct answer is A. mRNA is messenger RNA. This type of RNA carries the genetic information

copied from DNA in the form of codons, or three-base code segments. Transfer RNA (tRNA) deciphers

the code in the mRNA. Ribosomal RNA (rRNA) matches the correct protein to the code.

35. When propane is reacted in the presence of oxygen gas, the products of this combustion reaction

are:

a. C + H2

b. CH2 + H2O

c. CO2 + H2

d. CO2 + H2O

The correct answer is D. Combustion reactions always result in carbon dioxide and water.

36. Which of the following are decomposition reactions?

1) CH4 (g) + O2 (g) → CO2 (g) + H2O (l)

2) CaO (s) + CO2 (g) → CaCO3 (s)

3) Mg (s) + O2 (g) → MgO (s)

4) PbCO3 (s) → PbO (s) + CO2 (g)

a. 2 and 3

b. 2, 3, 4

c. 4

d. All are decomposition reactions

The correct answer is C. Reaction 1 is a combustion reaction. Reaction 2 is a synthesis reaction.

Reaction 3 is also a synthesis reaction. Reaction 4 is the only option where a compound is decomposed,

or broken down.

37. The products of a reaction are CO2 + H2O. Which type of reaction is this most likely to be?

a. Synthesis

b. Decomposition

c. Single replacement

d. Combustion

The correct answer is D. This reaction is most likely a combustion reaction since the products are

carbon dioxide and water. It could be a decomposition reaction, but combustion is more likely.

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38. The chemical equation, KClO3 → KCl + O2, is an example of which type of reaction?


b. Double replacement

c. Combustion

d. Decomposition

The correct answer is D. In this reaction, one compound is broken down into its two parts, that if re-

bonded would result in the reactant.

39. Combination reactions always:

a. Use only one reactant

b. Involve an element and an ionic compound

c. Form only one product

d. Require oxygen gas

The correct answer is D. Combustion reactions always have water and carbon dioxide as the products

and must have oxygen with a carbon-based compound as the two reactants.

40. In a double replacement reaction:

a. Energy in the form of heat or light is often produced

b. The reactants are usually a metal and a nonmetal

c. A gas, solid precipitate or compound forms in the exchange of ions

d. All statements are true

The correct answer is C. A double replacement reaction is a reaction in which a gas, a solid precipitate,

or a molecular compound forms from the exchange of ions between two compounds.

41. The chemical equation, Cr + Fe(NO3)2 → Fe + Cr(NO3)3, is an example of which type of reaction?


b. Decomposition

c. Double replacement

d. Combustion

The correct answer is A. Cr and Fe take each other’s place in the reaction. This is only one pair of

elements changing places, which means it is a single replacement reaction.

42. This region of the atom holds the protons.

a. Nucleus

b. Orbitals

c. Electron cloud


The correct answer is A. The nucleus holds the protons and neutrons, and is also where the mass of

the atom is.

43. Which subatomic particle does not contribute to an atom’s mass?

a. Proton

b. Neutron

c. Electron

d. All contribute to the atom’s mass.

The correct answer is C. Electrons are so small that any mass they may have is negligible. The protons

and neutrons are in the nucleus, which is what accounts for the mass.

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44. A piece of cork has a volume of 23.5 cm3 and a mass of 5.7g. What is its density?

a. 0.243 g/cm3

b. 4.123 g/cm3

c. 133.95 g/cm3

d. None are correct

The correct answer is A

Formula: D = m/v Solving for: Density

m = 5.7 g v = 23.5 cm3

D = m/v D = 5.7g/23.5cm3 D = 0.243 g/cm3

45. A student performs an experiment with three unknown fluids and obtains the following

measurements. Choose the correct order of the liquids based on how they would separate in a

beaker, listed from bottom to top.

Fluid A: m = 2060 g, V = 2000 mL Fluid B: m = 672 g, V = 850 mL

Fluid C: m = 990 g, V = 1100 mL

a. A, B, C

b. A, C, B

c. C, A, B

d. B, A, C

The correct answer is B. Fluid A has the highest density, which means it would be on the bottom,

followed by the next dense (fluid C). Fluid B would be at the top since it is the least dense.


Fluid A m = 2060 g v = 2000 mL

D = 2060g/2000mL D = 1.03 mL

Fluid B m = 672 g v = 850 mL

D = 672g/850mL D = 0.791 g/mL

Fluid C m = 990 g v = 1100 mL

D = 990g/1100mL D = 0.9 g/mL

46. There is a block on your desk that acts as a paperweight. Its measurements are 3 cm by 4 cm by 6

cm. The block has a mass of 184.32 g. What is its density?

a. 13271.04 g/cm3

b. 2.56 g/cm3

c. 0.39 g/cm3

The correct answer is B.


m = 184.32 g v = 3 x 4 x 6 = 72 cm3

D = m/v D = 184.32g/72cm3 D = 2.56 g/cm3

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47. What is the mass of the ethyl alcohol that exactly fills a 200.0 mL container? The density of ethyl

alcohol is 0.789 g/mL.

a. 157.8 g

b. 253.49 g

c. 0.0039 g

d. None are correct

The correct answer is A.

Formula: D = m/v; m = D*v Solving for: Mass

D = 0.789 g/mL v = 200 mL

m = D*v m = 0.789g/mL * 200mL m = 157.8 g

48. What volume of silver metal will weigh exactly 2500.0 g. The density of silver is 10.5 g/cm3.

a. 26250 cm3

b. 238.1 cm3

c. 0.0042 cm3

d. None are correct

The correct answer is B.

Formula: D = m/v; v = m/D Solving for: Volume

m = 2500 g D = 10.5 g/cm3

v = m/D v = 2500g/10.5g/cm3 v = 238.1 cm3

49. A flask that weighs 345.8 g is filled with 225 mL of carbon tetrachloride. The weight of the flask and

carbon tetrachloride is found to be 703.55 g. From this information, calculate the density of carbon

tetrachloride.

a. 1.59 g/mL

b. 2.76 g/mL

c. 1.4 g/mL

d. None are correct

The correct answer is A.


m (empty flask) = 345.8 g m (flask and solution) = 703.55g To find the mass of solution, subtract: 703.55 – 345.8 = 357.75g *This excludes the mass of the flask that was needed simply to contain the solution for measurement v = 225 mL

D = m/v D = 357.75g/225 mL D = 1.59 g/mL

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50. 28.5 g of iron shot is added to a graduated cylinder containing 45.5 mL of water. The water level rises

to the 49.1 mL mark, from this information, calculate the density of iron.

a. 0.63 g/mL

b. 7.92 g/mL

c. 0.58 g/mL

d. None are correct

The correct answer is B


m=28.5 g v (before adding iron) = 45.5 mL v (after adding iron) = 49.1 mL v (iron only) = 3.6 mL *since the iron is irregularly shaped, water displacement can be used to easily obtain volume. Subtract the ending water measurement minus the beginning water amount to get the volume of the iron.

D = m/v D = 28.5g/3.6mL D = 7.92 g/mL

51. Subatomic particles consist of:

e. Isotopes

f. Ions

g. Protons, Neutrons, and Electrons

h. Elements

The correct answer is C. The subatomic units are what give atoms their properties and consist of

protons, neutrons, and electrons.

52. Which of the following is true of elements?

e. They are substances made of 100% of the same type of atom

f. When neutral, they are substances in which the number of protons and electrons are identical

g. The positively charged protons and negatively charged electrons are responsible for the

attraction of atoms within an element

h. All of the above are true

The correct answer is D. Elements consist of the same types of atoms, and unless they are isotopes,

the number of protons and electrons are the same. Choice C is also true as it is the attraction between

the positively charged protons and the negatively charged electrons that holds the atom together.

53. Which groups of elements on the periodic table are considered main group elements?

e. Groups 1, 2, 13, 14, 15, 16, 17, and 18

f. Groups 1, 2, 14, 15. 16, 17, and 18

g. Groups 13-18

h. Groups 1-2

The correct answer is A. Main group elements: active metals in columns (also called groups) 1

and 2 as well as the metals, semimetals and nonmetals in columns (also called groups) 13-18.

54. What are transition metals?

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e. Elements that serve as a transition between group 1 and 2 elements.

f. Elements that serve as a transition between the two main group elements

g. Elements that serve as a transition between lanthanides and actinides

h. Elements that have electrons which do not transition between orbitals

The correct answer is B. Transition elements are located in the middle of the periodic table and serve as

a transition between the main group elements.

55. In which order do electrons fill orbitals?

e. 1, 2, 3, 4

f. a, b, c, d

g. 2, 2, 6, 6

h. s, p, d, f

The correct answer is D. The order of orbitals is s, p, d, f. Electrons fill the lowest energy state before

moving to higher energy states.

56. Which of the following is the correct electron configuration of Chlorine?

e. 1�"2�"2AB3�"

f. 1�"2�"2AB3�"3AC

g. 1�"2�"2AB3�"3AB

h. 1�"2�"2AB3�"3AB4�"

The correct answer is B. Coefficients 1, 2, 2, 3, and 3 are energy levels of Cl. As you can see "p" sub

shell can have maximum 6 electrons. Superscripts 2, 2, 6, 2 and 5 are electrons in the sub shells "s" and

"p".

57. What applications does molecular weight have in chemistry?

e. It is used to determine how many grams are in one mole of a substance

f. It is used to determine an element’s state of matter

g. It is used to determine electron configuration

h. It is used to determine entropy

The correct answer is A. Molecular weight is used to calculate the quantity of a substance present.

58. Determine the molecular weight of the caffeine molecule with formula CDH�ENGO"

e. 182.1906 g/mol

f. 170.1906 g/mol

g. 194.1906 g/mol

h. 206.1906 g/mol

The correct answer is C. (8*12.0107) + (10*1.00794) + (4*14.0067) + (2*15.9994) = 194.1906

59. Determine the molar mass of table salt NaCl

e. 58.44 g/mol

f. 81.43 g/mol

g. 58.44 amu

h. 81.43 amu

The correct answer is A. NaCl has 1 Sodium atom and 1 Chlorine atom, therefore:

(1*22.99)+(1*35.45)=58.44 g/mol

60. Convert 25g KMnO4 to moles

e. .929 mole

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f. 2.73 mole

g. .158 mole

h. .169 mole

The correct answer is c. The molar mass of KMnO4 is 158.034 grams/mole therefore,

25g/158.034g/mol= .158 mol

61. Of the below, which element is most electronegative?

e. K

f. Fe

g. Cl

h. Ne

The correct answer is D. Electronegativity increases as you move from left to right and from bottom to

top of the periodic table.

62. What characteristic is true for polar substances?

e. Polar substances have low freezing points

f. Polar substances have uneven electron distribution

g. Polar substances are composed of transition metals

h. Polar substances have a high affinity for non polar substances

The correct answer is B. Polar substances are characterized by uneven electron distribution – polar

substances have at least one area with a partial positive charge and at least one area with a partial

negative charge.

63. Which of the following properties of water is due to hydrogen bonds within the molecule?

e. Strong surface tension

f. High specific heat

g. High heat of vaporization

h. All of the above

The correct answer is D. The hydrogen bonds in water give it unique characteristics. All of the above

are true in addition to hydrophobic effect also being a unique characteristic.

64. Which of the following characteristic are true of conjugate acids and bases?

e. They gain and lose electrons equally

f. They gain and lose protons equally

g. They gain and lose neutrons equally

h. None of the above

The correct answer is B. For a reaction to be characterized as a conjugate acid-base reaction, it must

gain and lose protons equally.

65. Which of the below is true of conjugate pairs?

e. They may either be “base + conjugate acid” or “acid + conjugate base”

f. They may either be “acid + base” or “conjugate acid + conjugate base”

g. If one member of the pair is very strong, the conjugate member of the pair is usually weak

h. More than one of the above are true

The correct answer is D. Both A & C are true statements. Conjugate pairs comprised of one reactant

and one conjugate of the opposite pH classification (acid or base). Another helpful checkpoint in

determining conjugate pairs is to look at strength. If an acid reactant is very strong, its conjugate base

counterpart will likely be weak. The reverse is true as well.

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66. How are conjugate pairs identified?

e. The conjugate acid to the reactant base will have lost a hydrogen ion

f. The conjugate acid to the reactant base will have gained a hydrogen ion

g. The conjugate base to the reactant acid will have gained a hydrogen ion


The correct answer is B. For a base + conjugate acid pair, the conjugate acid will have gained a

hydrogen ion with respect to the base reactant.

67. How are redox reactions classified?

e. Redox reactions involve the transfer of elections and change of oxidation numbers

f. Redox reactions involve the transfer of hydrogen ions and change of oxidation numbers

g. Redox reactions involve the translocation of conjugate pairs

h. None of the above

The correct answer is A. For a reaction to be characterized as a redox reaction, electrons must be

transferred. A way to observe the transfer of electrons is to observe changes in oxidation numbers

between products and reactants.

68. The rules for determining oxidation number are many and complex. Below is a list of the rules – some

of which are TRUE and some of which are FALSE.

10. Free elements always have an oxidation number of 0.

11. Monoatomic ions always have oxidation numbers equal to the charge of the ion.

12. Hydrogen’s oxidation number is +1 unless it is combined with less electronegative


13. In compounds, oxygen has an oxidation number of -2, with the exception being that it is -

1 when in peroxides.

14. Group 1 elements have an oxidation number of 0

15. Group 2 elements have an oxidation number of +1

16. Group 17 elements in binary compounds have an oxidation number of -1

17. The sum of oxidation numbers of all of the atoms in a neutral compound must equal 0. 18. The sum of oxidation numbers in a polyatomic ion must equal to the charge of the ion.

Which are FALSE?

e. 2 and 7

f. 2 and 5

g. 5 and 6

h. 6 and 9

The correct answer is c. Group 1 elements have an oxidation number of +1. Group 2 elements have an

oxidation number of +2.

69. Which of the below are redox reactions?

e. 2Fe2O3(s)+3C(s)→4Fe(s)+3CO2(g)

f. NaCl+AgNO3⟶AgCl +NaNO3

g. 3C2H2⟶C6H6

h. HCl+H2O⟶Cl−+H3O+

The correct answer is a. There is a difference in oxidation number between products and reactants.

70. Assign oxidation numbers to each element of this compound: Na2SO4

e. Na=+1, S=+1, O=-2

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f. Na=+2, S=-2, O=0

g. Na=0, S=0, O=+2

h. Na=+1, S=+6, O=-2

The correct answer is D. Sodium is monoatomic which means its oxidation number is +1. Oxygen has

an oxidation number of -2 when in compounds other than peroxides. To solve for S, note that the sum of

oxidation numbers of all of the atoms in a neutral compound must equal 0. So, (2(+1)) + S + (4(-2)) = 0.

S=6.

71. The combined gas law:

e. Is a combination of Boyle’s law, Charles’s law, and Avogadro’s Law

f. Is represented by �� !" = �" "!�

g. Neither are true

h. Both are true

The correct answer is d. Choices A & B are both defining characteristics of the combined gas law.

72. A gas has a volume of 23L at 200K and 12 atm. What would the volume of the gas be at 300K and 14

atm?

e. 20L

f. 29.6 L

g. 30.2 L

h. Unable to determine with the information given

The correct answer is b. To solve for the new volume: V2 = (P1V1T2) / (T1P2)

73. The ideal gas law

e. Is used to predict the behavior of gas under many conditions

f. Has the formula PV=nRT

g. Uses Avogadro’s constant of 6.02214086 × 1023 mol-1


The correct answer is d. The ideal gas law predicts the behavior of gases under many conditions. In the

ideal gas law equation (stated above in choice B), R is Avogadro’s constant.

74. What is the pressure exerted by 4 moles of nitrogen gas contained in a 30 L container at 298K? e. 39, 736 atm f. 2.3927973e+25 atm

g. 3.26 atm h. None of the above

The correct answer is c. To solve for pressure: ((4)(.0821)(298))/30 75. Specific heat

e. Is the amount of energy required for a substance to boil f. Is twice the sum of the energy of the chemical bonds within a molecule g. Is generally higher in lanthanides than actinides h. Is the amount of energy required to raise 1 gram of substance by 1 degree Celsius

The correct answer is d. Specific heat is the amount of heat (energy) required to raise 1 gram of substance by 1 degree Celsius.

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76. The temperature of an unidentified metal with a mass of 63.4g increased from 25C to 48C as the

metal absorbed 849J of heat. What is the specific heat of this metal?

e. .45 J/gC

f. .55 J/gC

g. .65 J/gC

h. .75 J/gC

The correct answer is b. To solve for specific heat: 849J divided by (63.4g times 23C)

ready for the hesi...matter is anything that occupies space and has mass. all matter is made up of...

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