chang unit 1 chapters 1 & 3

8/2/2019 Chang Unit 1 Chapters 1 & 3

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Unit I: Ch. 1 & 3

Review of IntroductoryChemistry

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ChemicalFoundations

CHAPTER 1

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1. Introduction

2. Classification of Matter

3. Prefixes

4. Density

5. Scientific Notations (quick review)

6. Significant Figures

7. Dimensional Analysis

KEY CONCEPTS

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Chemistryis the study of matter and the

changes it undergoes

The scientific methodis a systematic approach

to research and discovery

A hypothesisis a tentative explanation for a set

of observations

A hypothesisbecomes a theoryif there are

many experimental results that upheld it

What is Chemistry?


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Common Prefixes and Values

Memorize these symbols & their meaning!!

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Density has unit of mass per volume

In a system of 2 phases, the denser phase will

sink and the less dense phase will float

Density of oil vs. water? Ice vs. water?

Density of water is ~ 1 g/mL (d depends on T)

Memorize: 1 mL = 1 cm3

density =mass

volumed=

mV

Density

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Scientific Notation

Used to express values too small or too big

Ex: 602,200,000,000,000,000,000,000= 6.022 x 1023

N, base #, a numberbetween 1 and 10

n, exponent, is a positive

or negative integer

N x 10n

N, base #, determines the # of significant figures

for the whole scientific notation


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Scientific Notation Manipulation

Converting normal notation to scientific notation:

1. Move decimal point (dp) so that 1 < N < 10

2. If dp is moved left, exponent n will be positive

3. If dp is moved right, exponent n will be negative

4. The value of n = # of digits dp is moved

5. If there is not a dp in a number, imagine it beingat the end of the number

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Ex 1: 568.762 = 5.68762 x 102

(dp is moved 2 digits to left n = +2)

Ex 2: 0.00000772 = 7.72 x 10-6

(dp is moved 6 digits to right n = -6)

Ex 3: 215300000 = ?

Ex 4: 2.37 x 10-3 = ?

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Addition or Subtraction

1. Write each quantity with the same exponent n2. Combine N1 and N23. The exponent, n, remains the same

Ex: 4.31 x 104 + 3.9 x 103 =

4.31 x 104 + 0.39 x 104 = 4.70 x 104

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Multiplication

1. Multiply N1 and N22. Add exponents n1 and n2

(4.0 x 10-5) x (7.0 x 103) =(4.0 x 7.0) x (10-5+3) =

28 x 10-2 =2.8 x 10-1

Division

1. Divide N1 and N22. Subtract exponents n1 and n2

8.5 x 104 5.0 x 109 =(8.5 5.0) x 104-9 =

1.7 x 10-5


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Significant Figures (sf)

1. Needed to indicate the certainty of a measurement

Ex: 2.00 kg is scientifically not the same as 2.0 kg

2. Any value obtained from measurement (using an

instrument) has a limited # of sf

Ex: T, V, m measurements

3. Values obtained NOT using an instrument

(counting, exact #, by definition) have an infinite

(unlimited) # of sf

Ex: 10 people in this room, 1 L = 1000 mL142/23/2010

Significant Figures (sf)

4. How many sf a measurement should have?

All measurements must have 1 (and only 1)

uncertain digit Read all the readable (certain)

digits up to including the first guessed digit

Ex: Read the T of this room in F (~ 75 C) using a

thermometer calibrated to tenths of a degree (10

divisions between one degree and next). How

many sig. fig. should the measurement have?

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Rules for Significant Figures1. Any digit that is not zero is sf

1.234 kg 4 significant figures

2. Captive zeroes (between nonzero digits) are sf

60006 m 5 significant figures

3. Leading zeroes are never sf

0.08 L 1 significant figure

4. Trailing zeroes are sf only if there is a decimal

point; if not they are not sf

0.00420 mg 3 significant figures

12000 g 2 significant figures162/23/2010

How many sf in each of the following measurements?

24 mL

3001 g

0.0320 m3

6.4 x 104 molecules (careful!)

560 kg

How to write 64,000 with 4 sf?


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Significant Figures in Calculations

Addition and Subtraction

The answer must have the same number of decimal

places (not sf) as the value that has the least # of

decimal places. From here, the # of sf in the final

answer can be determined

89.332 (3 dp)1.1 (1 dp)+

90.432 = ?

3.70-2.9133

0.7867 ?

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Significant Figures

Multiplication or Division

The number of significant figures in the result is set

by the number that has the smallestnumber of

significant figures

4.51 x 3.6666 = 16.536366 = ?

6.8 112.04 = 0.0606926 = ?

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Significant Figures

Many calculations involved

Apply the rule of sf one step at a time. The # of sf

in the final answer depends on the rule of the last

calculation

2.37 x 1.500 12.007 = ?= 16.536366 12.007 = ?

(0.0840 0.08206)

0.08206X 100% = ?

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Accuracy how close a measurement is to the truevalue

Precision how close a set of measurements are to each other

Accurate &precise

Precise butnot accurate

not accurate &not precise

In an unknown determination, accuracy is not known; can

only know precision consistent results are needed


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Dimensional Analysis As Method ofSolving Problems

1. To clearly show how result is obtained, and for the work to

be understandable by everyone (universal meaning)

2. Determine which conversion factor(s) are needed (can

convert one unit at a time, independently of other units)

3. A conversion factor is a ratio, = 1, has 2 different units

4. Carry units through calculation; cancel identical units

5. If all units cancel except for the desired unit(s), then the

problem was solved correctly.

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How many atoms of P are there in 2.50 g Ca3(PO4)2,MM =310.18 g/mol?

What is 2500 sf2 in cm2? 1 ft = 0.3 m (exactly)

Ex: The speed of sound in air is about 343 m/s. Whatis this speed in miles per hour? (1 mile = 1609 m)

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Stoichiometry

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1. Mole Concept

2. Molar Mass & Mass-Mole Conversion

3. Percent Composition

4. Empirical Formula & Molecular Formula

5. Stoichiometry

6. Limiting Reagent/Reactant

7. % Yield

KEY CONCEPTS


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Atomic mass: mass of an atom, depends on p+ & n

Ex: C-12 has atomic mass of 12.00 amu

C-13 has atomic mass higher than 12.00 amu

H-1 has atomic mass of 1.008 amu

Some elements have isotopes: C-12, C-13, C-14,

each have different atomic mass

Average atomic mass: mass of an atom takinginto account all the isotopes and their abundance

Atomic Mass

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Natural lithium is:

7.42% 6Li (6.015 amu)

92.58% 7Li (7.016 amu)

7.42% x 6.015 + 92.58% x 7.016 = 6.941 amu

Average atomic massof lithium:

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QUESTION

The atomic mass of rhenium is 186.2. Given that

37.1% of natural rhenium is rhenium-185, what

is the other stable isotope?

1)183

75Re 4)

181

75Re

2)187

75Re 5)

190

75Re

3)189

75Re

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The mole (mol)is the amount of a substance that

contains as many elementary entities as there are

atoms in exactly 12.00 grams of 12C

1 mol = NA = 6.0221367 x 1023

(NA): Avogadros number

The Mole


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Molar mass: mass of 1 mole of an element or

compound in grams Molar mass for a given

compound is a constant

1 mole 12C atoms = 12.00 g 12C

1 mole lithium atoms = 6.941 g of Li

Molar mass of a compound = sum of molar

masses of all atoms in the compound

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atomic mass (in amu)Molar mass (in g/mol)

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One Mole of:

C S

Cu Fe

Hg

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Which of the following is closest to the

average mass of one atom of copper?

a) 63.55 g

b) 52.00 g

c) 58.93 g

d) 65.38 g

e) 1.055 X 10-22 g


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Which of the following 100.0 g samplescontains the greatest number of atoms?

1. Magnesium

2. Zinc

3. Silver

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How many atoms are in 0.551 g of potassium (K) ?

How many H atoms are in 72.5 g of C3H8O ?

How many molecules are in 72.5 g of C3H8O ?

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M= molar mass in g/mol

NA = Avogadros number

variable const. variable const. variable

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Light

Light

Heavy

Heavy


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Percent compositionof an element in a cmpnd =

nx atomic mass of elementmolar mass of compound

x 100%

Atomic mass of O = 16.00 g/mol, not 32.00 g/mol

n: number of moles of an atom in 1 mole of the

compound (i.e., n is the subscript of the atom inthe compound)

total mass of elementtotal mass of compound

x 100% =

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C2H6O

%C =2 x (12.01 g)

46.07 gx 100% = 52.14%

%H =6 x (1.008 g)

46.07 gx 100% = 13.13%

%O =1 x (16.00 g)

46.07 g

x 100% = 34.73%

52.14% + 13.13% + 34.73% = 100.0%

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Evaluate Your Answer

Is it always true that a larger subscriptfor oxygen in a compound leads to a

greater percent oxygen by mass in acompound?

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Emperical Formula vs. Molecular Formula

Emperical formula: a formula that gives the relative

ratio of atoms in a molecule

Should always be written as (CxHyOz)n where n =

1,2,3,4.

Molecular formula: a formula that clearly gives the #

of atoms in a molecule, hence also their ratios

To determine molecular formula, the emperical

formula and molar mass have to be known


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Emperical formula of a cmpnd can be determined if

the % composition is known (and vice versa)

STEPS:

1. Assume the % composition of each element in the

compound is the mass of that element

2. Determine the moles of each element

3. Divide moles of each element by the smallest

moles get ratio of moles of elements making up

the cmpnd empirical formula

4. Dont round up in step 3; instead multiply moleratios by an integer to make all mole ratios integers

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Ex : A compound is made up of 81.8% C and the restis H. What is the empirical formula of the compound?

Ex: A compound is known to make up of C, H and N.The %C = 65.47%, %H = 9.09%. If the molar massof the compound is 111 g/mol, what is its molecular

formula?

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3 ways of representing the reaction: pictures, words, symbols

Chemical Equations

A chemical equationuses chemical symbols to show the

changes in a chemical reaction (not how it happens)

reactants products

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How to Read Chemical Equations

2 Mg + O2 2 MgO

2 atoms Mg + 1 molecule O2 makes 2 molecules MgO

OR 2 moles Mg + 1 mole O2

makes 2 moles MgO

OR 48.6 grams Mg + 32.0 grams O2 makes 80.6 g MgO

BUT IS NOT

2 grams Mg + 1 gram O2 makes 2 g MgO

IS


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Balancing Chemical Equations

1. Start with the most complicated cmpnd first

2. Change the numbers in front of the formulas

(coefficients) to make the number of atoms of

each element the same on both sides of the

equation. Do not change the subscripts.

3. Repeat step 2 for all cmpnds in the equation

4. Check to make sure that every atom is balanced.

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Ex 1: C3H6O2N + O2 CO2 + H2O + NO2

Ex 2: Al4C3 + H2O Al(OH)3 + CH4

Ex 3: PCl3 + H2O H3PO3 + HCl

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1. Write balanced chemical equation

2. Convert mass of known substances into moles

3. Use coefficients in balanced equation to convert to the

number of moles of compound sought

4. Convert moles of compounds sought into mass

Mass Changes in Chemical Reactions

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Ex 1: If 209 g of methanol are used up in the combustion

reaction below, what mass of water is produced?

2CH3OH + 3O2 2CO2 + 4H2O

Ex 2: When 20.0 g NH3 is reacted with excess oxygen, how

many grams of NO can be produced?

4NH3 + 5O2 4NO + 6H2O


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6 red left over

Limiting Reagents

Reactant that will be used up first; opposite of excess

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Mass Changes in a rxn with a Limiting Reactant

1. Using mass of each reactant, calculate the massof a common product formed (2 values obtained)

2. The smaller amount calculated (of the 2) is theamount of product that will be formed

3. The reactant giving this amount of product is thelimiting reactant

4. What is the meaning of the larger amount?

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Ex 1: 124 g of Al is reacted with 601 g of Fe 2O32Al + Fe2O3 Al2O3 + 2Fe

Calculate the mass of Al2O3 formed. Which is limiting?

Ex 2: 12.0 g NaCl and 21.0 g H2SO4 are reacted

2NaCl + H2SO4 Na2SO4 + 2HCl

Calculate the mass of acid formed. Which is limiting?

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Properties of a reaction (always


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Ex 1: A 5.95-g sample of AgNO3 is reacted with 6.52 g

BaCl2 according to the equation:

to give 3.14 g solid. What is the percent yield of the

reaction?

3 2 3 22 ( ) ( ) 2 ( ) ( ) ( ) AgNO aq BaCl aq AgCl s Ba NO aq+ +

Ex 2: When 150g ammonia is reacted with 150g oxygen,

87g of NO is obtained. Is the reaction efficient?

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g).

chang unit 1 chapters 1 & 3

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