[notes]chem15.1 - fundamentals of chemistry: laboratory

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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory

1

the curved surface of the water iscalled the meniscus

to read the volume of a liquid, keepyour eye on the same level with thelowest point of the meniscus

decantation is a process of separating a liquid from a denseinsoluble substance by pouring off the liquid

the liquid that is poured off during decantation is called the supernatant liquid

the separation of a solid from a liquid by passing the liquid through a

membrane is called filtration the liquid that passes the membrane is called the filtrate while the remaining

solid is called the residue

trailing zeros (zeros at the end after the decimal point) are significant

captive zeros (zeros within non-zeros) are significant

leading zeros before a decimal point are not significant but significant after the decimal point

final zeros that denote exact numbers are significant; not significant if the

number is only an approximation an exact number has an infinite number of significant figures

add or subtract decimals then round it off to the nearest least number of digits

multiply or divide decimals and reduce it to the least number of significantfigures in one of the dividend/divisor/factor

Measurements

quantitative observation

to be meaningful it must consist of a number and a scale expands by what our senses can perceive

SI System of Measurement

organized to standard systems of measurement in the world

made to avoid confusion created by the existence of metric and Englishsystem

SI Prefixes Common to Chemistry

Prefix Unit Abbr. Exponent

kilo 103

deci

10

-1

centi 10-2

milli 10-3

micro 10-6

Metric conversions – conversions in

Note: Graduated glassware canonly accurately measure liquids of

10% to 100% of its volume.Note: Use the forefinger in using apipette.

Note: A parallel-oriented plug givesa voltage of 220V while a straightplug gives a voltage of 110V.

Physical Quantity Unit

Length meter ()

Mass kilogram ()

Time second (

)

Temperature Kelvin ()

Luminous intensity candela ()

Electric current Ampere ( )

Amount of substance mole ()




2

the metric system are merely a matter of moving a decimal point. The “base unit”means that you have a quantity without a prefix.

Uncertainty in measurements

a digit that must be estimated is called uncertain

a measurement always has some degree of uncertainty

calibration is the difference among the smallest division

Precision and Accuracy

accuracy refers to the agreement of the measured value with the true value

expressed in % error

% =measured-true

true× 100%

a lower value means greater accuracy depends on the capacity of the instrument and its calibration as well as on

the person determining the instrument

precision is the agreement among values

expressed in terms of average deviation

measured-average

a lower value means greater precision

depends on the person making the measurement

Importance of the following steps addition of water – to dissolve the water-soluble component in the mixture

boiling the water – to further dissolve the water-soluble component

filtration – to separate the residue (water-insoluble component) from the filtrate(water-soluble component)

washing the residue with hot water – to ensure that all water-solublecomponent will be separated from the residue and transferred to the filtrate

evaporation – as water evaporates, the residue (water-soluble component) isleft behind, returns to its original state and thus capable of being weighed for subsequent calculations

Reminders during the experiment

use low blue flame when evaporating

to avoid splattering which could result to loss in mass of water-solublecomponent

further consequence is lower percentage of water-soluble component

weigh evaporating dish only when it is already cooled at room temperature

weighing while hot results in lower mass of water-soluble component

Errors in the experiment

low sensitivity of some instruments resulting in probable inaccuratemeasurements

basic assumptions like all water-soluble component are soluble and water-insoluble component remains insoluble in water

errors due to splattering and weighing of evaporating dish while hot

human errors




3

Graphs

quick way to represent data visually in a compact and convincing way especially useful in analyzing huge amounts of data

can be pie, linear, bar, cone, etc.

Reminders in making a good graph1] figure titles

should be appropriate with the data it represents

located below the graph

should have a period at the end

order of graphs is usually indicated by a number 2] labels of axes

-axis goes with the independent variable

-axis goes with the dependent variable

units of variables are also included and are enclosed in parentheses3] proper scaling observation

scales within each axis should be consistent; if differences in scaling is 5units, then use 5 all throughout, not 10 nor 2 in some parts of the axis

start your scale with a number slightly lower than the smallest data;similarly, end your scale with a number slightly higher than the largest data

use the lightning-like figure in axis when dealing with data that areenormously large; this will save up space and will make scaling relatively

easy4] best-fit curve

this is the line that goes through almost all data points

an advantage of using this line is that it excludes the errors of the data

Slope

∆ ∆

indicates the relative steepness of the line

the larger the slope value, the steeper the line

Interpolation process of locating points within the graph

usually the dependent variable is the one missing or to be calculated

only reliable if data projects a trend or set of data has minimum errors

starting from the -axis, a broken line is written until it reaches the line graph

and then projected into the -axis

the data on the -axis is the corresponding data for the -value in question

On preparing the graph1] indent the axes from the edge of the graphing paper 2] write the appropriate figure number and title of the graph below it3] identify the independent and dependent variables4] label each axis and indicate the units used5] choose an appropriate scale6] plot the points in the graph7] draw the (best-fit) curve




4

Matter is anything that occupies space and has mass.

Composition refers to parts or components of a sample of matter and their relative proportions. Composition is seen through the models, properties,similarity among elements/compounds) and differences amongelements/compounds.

Properties refer to qualities or attributes that can be used to distinguish onesample of matter from the other. This is usually established visually.

Physical Property is a property that a sample displays without changing itscomposition. Physical change refers to the change of physical appearance of asubstance. Some of the physical properties of a sample of a matter may change,but its composition remains unchanged. Phase change is also an example of

physical change.Chemical property refers to the ability (or inability) of a sample of a matter to

undergo a change in composition. Chemical change happens when a sample of matter is converted into a new sample with different composition. It can occur even without addition of a chemical or a reagent. Indications of chemical changeinclude evolution of gas, increase in temperature, change in color, and formationof precipitates.

Elements are homogenous pure substances that are made up of only oneatom. They cannot be broken down into simpler substances.

Compounds are homogenous pure substances that are made up of two or

more atoms. They can be broken down into simpler substances throughappropriate chemical means.

Homogenous pure substances have uniform composition and propertiesthroughout a given sample.

Homogenous mixtures have uniform composition ad properties throughout agiven sample, but the composition and properties may vary from one sample toanother.

Heterogeneous mixtures have components that are separated into distinctregions, making the composition and property vary from one mixture to another.

Homogenous substances cannot be easily identified as a mixture andtherefore needs a device like a microscope. Mixtures can be separated into itscomponents by appropriate chemical changes.

Boiling point

temperature at which the vapor pressure equals the standard atmosphericpressure

temperature at which liquid converts to a gas

the boiling point of pure substances is constant and straight; the boiling pointof mixtures varies across time

Intensive properties are independent of the quantity of matter under observation. Extensive properties are, by contrast, dependent of the quantity of matter

Electrons

located outside the nucleus and has a negative charge




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discovered by Eugene Goldstein

can probably be located 90% of the time in one of the orbitals

Quantum numbers

describe the orbitals

have discrete quantities (either an integer or half-integer

has four kinds

principal quantum number,

refers to the main energy levels which describes the probable distance of the electron from the nucleus

can take positive integer values starting from 0

angular momentum / azimuthal quantum number,

refers to the shape of the orbitals which is the surface that contains 90%of the total electron probability

can take positive integer values from 0 to − 1 o the orbital has a spherical shape centered around the origin of the three

axes in spaceo there are three dumbbell-shaped orbitals in each energy level above

= 1, each assigned to its own axis in spaceo things get a bit more complicated with the five orbitals that are found in

the sublevels beginning with = 3

magnetic quantum number, refers to the spatial orientation of the electrons

can take integer values from −ℓ to ℓ, including 0 spin quantum number,

refers to the electron spin which describes the behavior of an electronwithin a magnetic field

can take either + 12 or −1

2

An orbital is a region in the atomic space where the electron is most likely tobe found. It is characterized by a set of quantum numbers.

Pauli’s Exclusion Principle states that in a given atom, no two electrons can

have the same set of four quantum numbers.Aufbau Principle states that electrons would most likely occupy the lower

energy orbitals first before continuing to the next orbitals. Identifying the lower level orbitals is determined by the ( + ) rule, which states that the lower the

( + ℓ) value, the lower the energy of the orbital. In case of equal + ℓ, theorbital with the lower has the lower the energy.

Hund’s Rule states that every orbital in a subshell is singly occupied with oneelectron before any orbital is doubly occupied, and all electrons in degenerateorbitals have the same spin.

To get the valence electron configuration of an atom, identify the

corresponding orbitals of a given principal quantum number. Only thecorresponding orbitals of the last principal quantum number will be used for thevalence electron configuration.

To get the noble gas configuration of an atom, identify the electronconfiguration of the highest possible noble gas that is lower than the given atom.Then replace that part of the configuration found in the electron configuration of the atom with the chemical symbol of the noble gas enclosed in braces.




6

The effective nuclear charge, denoted as Zeff , is the net positive chargeexperienced by an electron in a many-electron atom. = − where is the

shielding constant exerted by the electrons.

* doesn’t applywith noble gases

Rules for namingbinary

compounds:

1] identify the elements present in the compound given by the chemical formula 2] change the suffix of the less metallic element to –ide* 3] use the prefix corresponding to the number of atoms present in the compound

* In accordance with established practice, the elements in a covalent compoundare placed and named first in the sequence: Rn – Xe – Kr – Si – Sb – B – As – P – H – Te – At – Se – C – I – Br – N – Cl – O – F

Rules for writing chemical formulas of binary compounds:1] represent each kind of element in a compound

2] indicate by a subscript the number of atoms of each element in a molecule of that compound3] write the symbol of the more metallic element first (H is an exception)

Rules for naming ionic compounds:1] write the name of the cation first, followed by the name of the anion2] write the suffix of the cation depending on the charge (refer to a table) and

replace the suffix of the anion with –ide

Rules for writing chemical formulas of ionic compounds:1] write the symbol of the cation followed by the symbol of the anion

2] balance the charge of the ions to have a net charge of 0 by adding or removing instances of ions

3] for hydrates, follow the chemical formula with a central dot and the correctamount of water molecules

Rules for naming binary acids

if a binary acid, fill the prefix of the anion to hydro_____ic

if an oxyacid…

if the anion ends in –ate, fill the prefix of the anion to _____ic acid

if the anion ends in –ite, fill the prefix of the anion to _____ous acid

A mole is a quantity that contains approximately 6.02×1023

particles. It isdefined as the quantity of a substance that contains the same number of particlesas are contained in precisely 12.00g of a particular isotope of Carbon, 12C.

Atomic Property Trends

Greater at lower-left Greater at upper-right

Atomic Size First Ionization Energy

Cation Formation Tendency* Anion Formation Tendency*

Electron Affinity*

Electronegativity




7

= =

no.of particles

Boyle’s Law states that at constant temperature, the pressure of a givenamount of gas is inversely proportional to its volume. The product of pressure

and volume is equal to a constant. = 1 Charles’ Law states that at constant pressure, the volume of a given amount

of gas is directly proportional to its absolute or Kelvin temperature. The ratio of

volume to the temperature is equal to a constant. = 2

Avogadro’s Law states that at a give temperature and pressure, the volumeof gas is directly proportional to the quantity of gas, in moles. The ratio of volume

to the amount of gas in moles is equal to a constant. = 3 Using all three laws, the result can be expressed in the terms of = ,

which is the ideal gas law, where is the pressure of gas (in atm), is the

volume of gas (in L), is the number of moles of gas, is the temperature (in

Kelvin), and is the ideal gas constant, which is equal to 0.0821∙∙.

In 1916, Gilbert Newton Lewis represented the structure of elements andcompounds by using the symbol of the elements, and dots representing valenceelectrons. This is later on referred to as the Lewis structure.

The Lewis structure of ionic compounds usually has the cation permanentlytransferring electrons to the anion, instead of atoms bonding.

The Lewis structure of covalent compounds usually has bonds that hold theatoms together in a molecule which are called covalent bonds, unlike in ioniccompounds.

The octet rule states that an atom other than hydrogen tends to form bond/suntil it is surrounded by eight valence electrons.General guidelines for writing Lewis structure of simple molecules

determine the number of valence electrons to be distributed in the Lewis

structure write a skeletal structure for the molecule indicating the arrangement of the

atoms and which ones are bonded to one another

place one pair of electrons between each bonded atom to make a single bondbetween each pair of bonded atoms

use the remaining electrons, place lone pair around the terminal atoms tosatisfy the octet rule

if there are still remaining electrons, place them around the central atom aslone pairs

move the electrons to form double or triple bonds in order to satisfy the octet

rule for the central atom

Resonance structures are Lewis structures of the same molecule that aresame in structure but have different electron and bond placement.

Three exceptions to the octet rule

incomplete octet have less than eight electrons surrounding the central atom




8

expanded octet have more than eight electrons surrounding the atom (byusing the d orbitals)

odd electron species or free radicals are species that have an unpairedelectron

The formal charges of atoms are apparent charges on atoms in a Lewisstructure. It is calculated using this:

formalcharge

=

number of valence electronsin the free atom

− number of

non-bondedelectrons

−

½ of the totalnumber of bondingelectrons

There are guidelines in selecting the most plausible resonance structure usingthe formal charges:

for neutral molecules, the Lewis structure with atoms bearing the lowest formalcharges (closest to zero) is most preferred

the most electronegative atoms in a Lewis structure should bear negativeformal charges while the least electronegative atoms should bear positiveformal charges

adjacent atoms in a Lewis structure should not have formal charges of thesame sign

Molecules are stable units formed by sharing electrons through intermolecular

bonding. They don’t exist in metals, ionic compounds or covalent networksubstances.

Intermolecular Forces of Attraction

forces causing aggregation of compounds of a substance to form a liquid or solid

occurs between rather than within molecules

responsible for changes in physical states

affects boiling point, vapor pressure, viscosity, and surface tension

Types of IMFA

London dispersion forces are weak and short-lived forces of attraction thatexists in all molecules

Dipole-dipole interaction exists in polar molecules which exhibit dipolemoment

Hydrogen bonding

strong dipole-dipole forces

seen in molecules where it is covalently bound to any of highlyelectronegative elements N, O, or F

objects are electrically charged by rubbing

electrical charges of opposite signs attract each other

Surface tension is a property possessed by liquid surface whereby theyappear to be covered by a thin elastic membrane in a state of tension.

For a given volume of a substance, the shape with the least surface area is asphere.




9

Solids are substances that have definite volume and shape. Pure solid

substances are classified into four different types: metallic substances

ionic solid

covalent molecular

covalent network

Electrical conductivity

ability to conduct electric current which requires movement of chargedparticles

differences in conductivity lie mainly on

the kind of particles present

forces of attraction existing between particles

Metals

structural unit is composed of positive ions, metal atoms, surrounded by sea of delocalized electrons

force of attraction that holds the metal atoms together is the metallic bonding, joined by extreme delocalized bonds

metals conduct electricity in their solid and molten state but in aqueous state,which are insoluble except for some which react

electron sea model is composed of…

cations – particles which form the crystal lattice; occupy fixed positions in alattice or array

sea of electrons – electrons list by metal atoms; electrons move freely in thelattice

The introduction of an electric field to the metal in its solid or molten statescauses these electrons to flow, producing electric current.

Ionic substances

structural unit is composed of ions bound by ionic bonding

ionic substances conduct electricity in their molten and aqueous state but not

in solid state electrolytic conduction occurs in ionic substances in the molten or aqueous

state.

Covalent molecular compounds

structural unit is composed of atoms or molecules bonded by covalent bondingand interacts using IMFA

covalent molecular substances do not conduct electricity in any state exceptfor some when dissolved in water

molecular compounds do not conduct electricity unless they react with H2O

(ex. HCl) to form ions; the molecules are electrically neutral and there are nocharged carriers

Covalent Network

structural unit is composed of atoms joined together by covalent bonding

covalent network substances do not conduct electricity in any state and areinsoluble in water




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graphite is an exception as each carbon is bonded to three other carbon andone electron is delocalized; diamond does not conduct electricity since each

carbon atom is bonded to four other carbon atoms

Energy is the capacity to do work.The law of conservation of energy states that energy can be converted from

one form to another but can neither be created nor destroyed.Potential energy is the energy due to the position or composition of the

substance while kinetic energy is the energy due to motion.Temperature is a property of substances that reflects the random motion of

particles in a particular substance while heat is the transfer of energy betweentwo objects due to temperature difference. Temperature reflects the intensity of

the random kinetic energy in matter while heat is the amount of energy availablefor heat flows depends on quantity of matter at a given temperature.

A cooling curve is a graphical representation of the changes of states withuniform removal of heat from a substance.

At 0 to 1, as heat is removed from the gas, the average kinetic energy of theparticles of the gas decreases and the temperature drops until the temperature is

reached at 1 where the gas starts to liquefy. The temperature at which the gasand liquid coexist is the liquefaction or condensation point of the substance. Theliquefaction point and the boiling point of a substance are, therefore, equivalent.

At 1 to 2, also known as the liquefaction/condensation point, there is nochange in the average kinetic energy of the particles and so the temperature of the substance stays constant. The heat removed is, therefore, compensated for by the release of the stored potential energy, decreasing the potential energy of the substance. The amount of gas naturally decreases and the amount of liquid

increases. Eventually, at 2, sufficient heat has been removed to convert all thegas to liquid.




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At 2 to 3, as heat is removed, the average kinetic energy of the particles of

the liquid decreases and the temperature drops until the temperature at 3 isreached where the liquid starts to solidify. The temperature at which the liquidand solid coexist is the freezing or crystallization point of the substance. Thefreezing point and the melting point of a substance are, therefore, equivalent.

At 3 to 4, also known as the freezing point, there is no chance in the

average kinetic energy of the particles and so the temperature of the substancestays constant. The heat removed is compensated for by the release of storedpotential energy, decreasing the potential energy of the substance, as the liquidparticles are converted to solid. The amount of liquid gradually decreases and

the amount of solid increases. Eventually, at 4, sufficient heat has been removed

to convert all the liquid to solid.

The Phenomenon of Supercooling At the expected freezing point of a substance, the particles may not be

oriented properly to fit the crystalline lattice. When heat continues to be removedfrom the substance in the absence of crystallization, the temperature of the liquiddrops down below its expected freezing point and the liquid is said to besupercooled. Once the correct pattern has been built up to sufficient size,additional particles may rapidly accumulate. Potential energy is suddenlyreleased and the energy that is evolved increases the average kinetic energy of the particles and the temperature rises until it coincides with the freezing point

after which the substance behaves normally.Supercooling may be reduced by the introduction of a seed crystal, on which

crystallization can occur, thereby initiating the proper structure. As some substances like glass, rubber and many plastics are cooled, their

molecules move so slowly that they never find the proper orientation to form thecrystalline solid and an amorphous solid results instead. Amorphous solids areactually supercooled liquids which do not have a sharp, well-defined meltingpoint, but instead gradually soften when heated.

A heating curve (see next page) is essentially the opposite of a cooling curve.It graphically illustrates the changes of states with uniform addition of heat to asubstance. The distance of the time axis is a measure of the amount of heatadded at a constant rate.

At 0 to 1, as heat is added to the solid, the motion (kinetic energy) of theparticles of the solid increases and the solid progressively becomes slightly lessordered. Since temperature measures kinetic energy, the temperature rises untilthe temperature is reached at 1 where the solid starts to melt. The temperatureat which solid and liquid coexist is the melting point of the substance.

At 1 to 2, also known as the melting point, there is no change in the average

kinetic energy of the particles and so the temperature of the substances staysconstant. The added heat is used to overcome the forces of attraction betweenthe particles of the solid and is thereafter stored as potential energy, increasingthe potential energy of the substance. The amount of solid gradually decreases

and the amount of liquid increases at this point. Eventually, at 2, sufficient heathas ben added to convert all the solid to liquid.




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At 2 to 3, as heat is added, the average kinetic energy of the particles of theliquid increases and the temperature rises until the temperature at 3 is reachedwhere the liquid starts to evaporate. The temperature at which liquid and gascoexist is the boiling point of the substance.

At 3 to 4, also known as the boiling point, there is no change in the averagekinetic energy of the particles and so the temperature of the substance staysconstant. The added heat is used to overcome the forces of attraction betweenthe particles of the liquid and is stored as potential energy, increasing thepotential energy of the substance. The amount of liquid gradually decreases andthe amount of gas increases. Eventually, at 4, sufficient heat has been added toconvert all the liquid to gas.

The Phenomenon of SuperheatingThe bubbles formed at the boiling point provide internal space at which the

liquid can evaporate. Bubbles form easily in a vessel with irregular inner surface.In a vessel with smooth inner surface, bubbles may not form easily so that theliquid is heated to a temperature above the boiling point without evaporation. Thisprocess is known as superheating.

At the first and second graphs of the cooling curve, the melting point range isobtained. This usually occurs when the substance contains impurities. At thethird graph, the temperature rise denotes that a substance has supercooled.




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Types of chemical reactions combination [A + B + ⋯ → C] reactions involve two or more elements or

compounds reacting to form a bigger compound

in a decomposition [A → B + C + D + ⋯] reaction, a single compound isbroken down into two or more simpler substances; usually requires heat whensolid is being decomposed

in a single displacement [AB + C → AC + B] reaction, either the cation or anion of an ionic compound is replaced by an uncombined element

double displacement [AB + CD → AD +C B] reaction

a precipitation reaction is a type of double displacement reaction wheretwo ionic compounds dissolved in water are combined to form two new onesby exchanging cations and anions with one another, with one of theresulting compounds soluble in water while the other is insoluble

a neutralization reaction involves the reaction between an acid and a baseto form water and a salt

combustion is a special type of reaction which involves the reaction of asubstance with oxygen and evolution of heat

Rules on solubility

most nitrates (NO3-) are soluble

most salts containing alkali metal ions (Li+, Na

+, K

+, Cs

+, Rb

+) and the

ammonium ion (NH4+) are soluble

most chlorides (Cl-), bromides (Br

-), and iodides (I

-) are soluble except Ag

+,

Pb2+

, and Hg22+

most sulfate salts are soluble except BaSO4, PbSO4, HgSO4, and CaSO4

most hydroxide salts are only slightly soluble while Ba(OH)2, Sr(OH)2, andCa(OH)2 are marginally soluble

most sulfide, carbonate, and phosphate salts are only slightly soluble

Chemical Equations represents the changes that take place during chemical

reactions.

Balancing chemical equations show substances that reacted andsubstances produced and the amount of each substance on both sides.

The coefficients before the substance denotes the relative amounts of substances involved.

2H2 + O2 → 2H2Oreactants products

Physical states of substances when balancing chemical equations includesolid, liquid, gas, and aqueous state.

Chemical Stoichiometry

quantitative relationship of the amounts of reactants and amount of productsformed

mass relationship expressed in a balanced reaction




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factors that limit the yield of products in a reaction are…

amount of starting reaction

percent yield of reaction which are affected by changes in pressure andtemperature

chemicals react according to fixed mole ratios

only a limited amount of product is formed from a given amount of startingmaterials

the limiting reactant is complete consumed and determines the amount of product formed while the excess reactant does not completely get used up ina reaction

A solution is a homogeneous mixture composed of a solute and a solvent.The solvent is the component that retains its state when solution is formed anddissolves the other component. When both components are liquid, the substancewith higher amount is chosen as solvent. The solute is the component beingdissolved by the solvent.

A solute is said to be soluble if it is a solid dissolved in the solvent while it issaid to be miscible if it is a liquid dissolved in the solvent.

A dissolution process is said to be exothermic if the process involvesreleasing of heat while it is said to be endothermic if the process involvesabsorption of heat.

Solubility refers to the maximum amount of solute that is dissolved in a givenamount of solvent at a given temperature. There are three factors affectingsolubility:

pressure

as pressure is increased, the number of collisions of gas particles with thesurface of the liquid increases, thus the rate of capture of gas molecules bythe liquid also increases

temperature

solubility of gases in liquids

as temperature is increased, there results in an increase in kinetic energyof the gas molecules, thus a large fraction of gas molecules will possess

the kinetic energy required enabling them to escape from the liquid solubility of solids in liquids

may either increase or decrease with the change in temperaturedepending on whether the solution process is endothermic or exothermic

if a dissolution is exothermic, then an increase in temperature willincrease the solubility of the liquid

if a dissolution is endothermic, then an increase in temperature willdecrease the solubility of the liquid

as temperature is increased, entropy is also increased; the dissolution of solids in liquid is thus favored because the liquid state is more disorderly

than the solid state nature of solute and solvent




15

Types of solutions based on the relative amount of dissolved and undissolvedsolute:

saturated, if a solution that contains the maximum amount of solute that candissolve in a given volume of solvent and has a concentration equal to thesolubility of the solute

unsaturated, if a solution contains an amount of solute less than its solubility

supersaturated, if the solution may contain an amount of solute greater thanits solubility under special conditions

There are three important interactions that operate in the solution process:

solute-solute interactions

attraction between the solute particles

in overcoming these forces of attraction that bind solute particles together,

energy must be supplied to the system solvent-solvent interactions

attraction between solvent particles

this is energy-requiring since you are pushing apart the solvent to providespace to accommodate solute particles

solute-solvent interactions

attraction between the solvent and solute particles

the formation of these forces of attraction should provide the energyrequired to overcome both the solute-solute and solvent-solvent interactions

the stronger the attractive forces between unlike molecules of particles, thegreater the solubility

a polar substance will most likely dissolve a polar substance while a nonpolar substance will most likely dissolve a nonpolar substance

A reduction-oxidation reaction, or simply redox reaction, is a reactionwhich involves the transfer of electrons from one substance to another.

Oxidation is a half reaction that involves the loss of electrons while reduction is a half reaction that involves the gain of electrons.

The oxidizing agent is a reactant which oxidizes the other reactant and whichundergoes reduction. The reducing agent is a reactant which reduces the other reactant and which undergoes oxidation.

The standard reducing potential table is a list of oxidizing agents, in order of

increasing strengths with corresponding potentials, denoted by °. ° isdetermined by comparing with the potential of standard hydrogen electrode (one

mole in aqueous solution or 1 for gases at 25°)

Identifying half reactions

reduction half-reaction (RHR) involves the gain of electrons; electrons

appear on the reactant side oxidation half-reaction (OHR) involves the loss of electrons; electrons

appear on the product side

On determining the reducing agent, oxidizing agent and their relative strengths

potential, also called voltage or electromotive force, unit: volts, is themeasure of the tendency of the half reaction to occur




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reduction potential is the tendency of species to acquire electrons; the morepositive the reaction, the greater is the tendency to occur

oxidation potential is the tendency of species to lose electrons

Voltaic/Galvanic Cell

named after Luigi Galvani andAlessandro Volta

an electrochemical device wherea spontaneous oxidationreduction takes place andgenerates electrical energy

salt bridge contains aconcentrated solution of a strong

electrolyte; thus ions diffuse outof the solution

the cation and the anion to beused should be about the samesize and of the same magnitudeso that they diffuse at the samerate; they must also be inert towards the solutions and towards the electrons

Cell Potential is the potential of overall reaction of the redox reaction. It iscomputed by getting the sum of the potentials of the two reactions.

The sodium hydroxide pellets should increase in mass after standing becauseit is hygroscopic. Thus, there is a need to standardize the sodium hydroxidesolution because its concentration would not be exactly 0.1M because its massincreased.

Rates of Reaction

change in concentration of a reactant on a per unit time

expressed in terms of the increase in the concentration of a product per unittime, or the decrease in concentration of reactant per unit time

Factors affecting rate of reaction

nature of reacting species

concentration

temperature

presence of a catalyst

Collision Theory of reaction rates

for a chemical reaction to occur, the reacting species should collide with eachother

the collision may or may not be effective; a collision is effective when it resultsin a chemical reaction

for an effective collision to occur…

reacting species must have a particular orientation during collision

the collision must occur with enough energy, called activation energy




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Reaction Pathways

Reaction pathway for an exothermicreaction

Reaction pathway for an endothermicreaction

Effect of concentration on rate of reaction

Reaction pathway for an uncatalyzedreaction

Reaction pathway for an catalyzedreaction

the catalyst lowers the energy barrier but does not affect the actual energy of products or reactants

state of equilibrium exists not only in gaseous systems but also in reactionsoccurring in solutions

a chemical equilibrium is a state where the concentrations of all thereactants and products remain constant with time

The following conditions exist when a process has reached a state of equilibrium:

a dynamic situation in which the forward and reverse processes continue totake place though the reaction appears to have stopped

a balance in which the rate of formation of the products is just equal to therate at which they are being decomposed

a definite mathematical relationship




18

if > 1, more of the product is formed, and the direction of the reaction is

forward

if < 1, more of the reactant is formed, and the direction of the reaction isbackward

if = 1, the reaction is in a state of chemical equilibrium

Effect of concentration (Fe3+ + SCN− ⇔ FeSCN2+)

increase of Fe3+ from Fe

NO33

increases the rate of forward reaction

increases in collisions to form more FeSCN2+ until another equilibrium isreacted

equilibrium shifts forward

a darker solution was observed because of the increase in FeSCN2+

increase of SCN from KSCN−

increases the rate of forward reaction

increases in collisions to form FeSCN2+ until another equilibrium is reached

increase in H2PO4−

decreases the concentration of free Fe3+ because of the reaction: Fe3+ +

H2PO4− ⇔ FeH2PO4

2+ (colorless)

Generalization: Increasing the concentration of a substance in equilibriummixture displaces the equilibrium in the direction which consumes some of theadded materials. Conversely, decreasing the concentration of a substance favors

the reaction which produces it.

Effect of pressure (2NO2 ⇔ N2O4)

the gaseous equilibrium is initially brown; initially after pushing the plunger…

brown color intensified because of the sudden compression of the gasmolecules

increase in gas pressure by sudden decrease in volume increases theconcentrations of both NO2 and N2O4 to the same degree thus the browncolor intensified

after few seconds, the color of the gas became light brown

when equilibrium has been reestablished, the resulting mixture is lighter incolor than the original

the rate of decomposition of N2O4 is not appreciably affected by change inits concentration upon the sudden compression but the rate of reaction of

NO2 molecules to form N2O4 is increased because it increased in number of molecules

Generalization: Increasing the pressure of the system by decreasing the volumeof container favors the reaction which produces the less number of molecules.On the other hand, decreasing the pressure by increasing the volume favors thereaction which increases the total number of molecules.

Reaction Quotient ()

similar to K but uses initial concentration

if Q < , the equilibrium shifts forward

if Q > , the equilibrium shifts backward




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if Q = K, there is no shift and the system is at equilibrium

Electrolytes are substances whose solutions in a given liquid contain positiveand negative ions regardless whether these ions existed in the pure solute or were formed in the process of solutions and are capable of conducting electricity.

Non-electrolytes are solutes whose solutions in a given liquid containmolecules and thus are non-conductors of electricity.

Covalent electrolytes are compounds which are not ionic but behave liketypical electrolytes when dissolved in water; thus they give solutions that containions.

Weak electrolytes do not dissociate completely in a solution while strongelectrolytes dissociate completely in a solution.

Strong acids; like HCl, H2SO4, HClO4, HI, HBr, and HNO3; and strong bases,which includes all hydroxides of Group 1 and 2 elements, are also strongelectrolytes.

Brønsted-Lowry acids and bases identify acids (a proton donor) and bases(proton acceptor) and their corresponding conjugate base and conjugate acid ina dissolution process.

Calculations of pH of strong and weak acids and bases

pH = − logH3O+

H

3O+

= 10−pH

pOH = − logOH− OH− = 10−pOH

pH + pOH = 14

A buffer solution is a solution whose pH remains almost constant despitedilution or addition of small amounts of either an acid or a base

After the dissociation of a weak acid/base into water, a conjugate base/acidand a conjugate acid/base will be formed. If a weak acid is dissociated into water,the ion from the acid becomes a conjugate base while water becomes hydronium

and a conjugate acid.If an acid is added to the (acid) buffer solution, the conjugate base neutralizes

it.If a base is added to the (acid) buffer solution, the acid neutralizes it.

Radioactivity is a phenomenon in which an unstable nuclei spontaneouslyemits various particles and/or electromagnetic radiation.

Rules in balancing chemical reactions:

the total number of nucleons in the products must be equal as that in thereactants

the total number of nuclear charges in the products and the reactants must bethe same




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Types of radioactive decay:

alpha emission involves the emission of a He24 or an α particle from an

unstable nucleus, resulting in a daughter nuclide with a mass number four lessand atomic number two less than the parent nuclide: XZA → JZ−2

A−4 + He24

beta (electron) emission is the emission of a high speed electron from anunstable nucleus and can be thought of as the conversion of a neutron to a

proton and electron with the emission of the electron: n01 → H1

1 + e−11

positron emission results in a daughter nuclide that has the same mass

number, but an atomic number one less than the parent nuclide: p11 → n0

1 + e10

electron capture occurs when an unstable nucleus captures an electron from

a core atomic orbital of an atom: p11 + e−1

1 → n01 + γ

gamma emission results from the loss of energy from an excited state of a

nucleus: XZA

→XZ

A +

γ

Rate of radioactive decay:The half-life for a radioactive decay is given by ln 2 over the decay constant, .

12

=ln 2

The relationship between the fraction of radioactive nuclei, 0, and time, , is

given by:

ln 0

= −

[notes]chem15.1 - fundamentals of chemistry: laboratory

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