Mole Review

1.) Calculate the number of moles in 60.4L of O2.

2.) How many moles are there in 63.2g of Cl2?

60.4L O2

22.4L O2

1 mol O2 = 2.7 mol O2

63.2g Cl2

70g Cl2

1mol Cl2 = 0.903mol Cl2

Ch. 9

Math In Chemistry

Stoichiometry

Tiny Tyke Tricycle Company

F + S + 3W + H + 2P → FSW3HP2

Scheduled to make 640 tricycles. How many wheels should they order?

Proportional Relationships

Proportional Relationships

I have 5 eggs. How many cookies can I make?

3/4 c. brown sugar1 tsp vanilla extract2 eggs2 c. chocolate chipsMakes 5 dozen cookies.

2 1/4 c. flour1 tsp. baking soda1 tsp. salt1 c. butter3/4 c. sugar

5 eggs 5 doz.2 eggs = 12.5 dozen cookies

Ratio of eggs to cookies

Proportional Relationships• Stoichiometry– mass relationships between substances in a

chemical reaction• for example: you can determine the amount of a

compound required to make another compound– based on the mole ratio

• Mole Ratio– indicated by coefficients in a balanced equation

2 Mg + O2 2 MgO2 Moles of magnesium react with 1 mole of oxygen to form 2

moles of magnesium oxide.

2 Mg + O2 2 MgO

What would be the mole ratio of magnesium to magnesium oxide?

2 : 2Conversion factor = 2 mol Mg

2 mol MgO What would be the mole ratio of oxygen to

magnesium?1 : 2

Conversion factor = 1 mol O2

(Mole Ratio) 2 mol Mg

Practice

5 F2 + 2NH3 N2F4 + 6HF1. What is the mole ratio of NH3 to F2? Write the mole ratio as a conversion factor.

2. What is the mole ratio of HF to N2F4?Write the mole ratio as a conversion factor.

2:5

2mol NH3

5mol F26:1

6mol HF1mol N2F4

Stoichiometry Steps1. Write a balanced equation2. Identify known & unknown.3. Convert known to mole (if necessary), line up

conversion factors.4. Use Mole Ratio.5. Convert moles to unknown unit (if necessary).6. Calculate and write units.

known

Mol of known

Mol of unknown

Mole ratio- get from equation

Mol of unknown

Units of unknown

Mole - Mole Stoichiometry

Formula: known mol mol unknown

mol known

1. Write the known and unknown.2. Use the balanced equation to find the mole

ratio.3. Calculate.

__S + __O2 → __SO3 Write the equation. Balance the equation. How many moles of SO3 are produced when

there are 4.5 moles of S? Known = Unknown =

Mole-Mole Examples

#1

2C3H7OH + 9O2 → 6CO2 + 8H2O Write the equation. Calculate the moles of oxygen needed to

react with 3.40 moles of isopropyl alcohol.

Mole-Mole Examples#2

Isopropyl alcohol (C3H7OH) burns in the air to this equation:

2C3H7OH + 9O2 → 6CO2 + 8H2O

Find the moles of water when 6.20 mol O2 reacts with C3H7OH.

Mole-Mole Examples

#3

Mass-Mass Stoichiometry• Mass of reactants equals the mass of products, Law of Conservation of Mass• ONLY mass and atoms are conserved in every chemical reaction

1. Write the known and unknown.2. Find the molar mass of the known and unknown substances.3. Use mole and molar mass conversion factors from Ch. 7 and mole ratios

from the balanced equation to solve.

Known g 1 mol Known

Molar massKnown

mol unknown

mol known

Mol ratio- get from equation

Molar mass unknown

1 mol unknown

Mass-Mass Stoichiometry

#1

The reaction of fluorine with ammonia produces dinitrogen tetrafluoride and hydrogen fluoride.

5F2 + 2 NH3 → N2F4 + 6HF

How many grams of NH3 are required to produce 7.38g HF?

Mass-Mass Stoichiometry

#2

5F2 + 2 NH3 → N2F4 + 6HF

How many grams of N2F4 can be produced from 265g F2?

Mass-Mass Stoichiometry

#3

2C2H2 + 5O2 → 4CO2 + 2H2O

How many grams of oxygen are required to burn 52.0g C2H2?

Volume-Volume Stoichiometry

• Formula to use:

Known (L) 1 mol known mol unknown 22.4 L unknown 1 22.4 L known mol known 1 mol unknown

1. Write the known and unknown.2. Use mole and volume conversion factors from Ch. 7 and the

mole ratios from the balanced equation to solve.

C3H8 + 5O2 → 3CO2 + 4H2O

If 25 liters of oxygen are consumed in the above reaction, how many liters of carbon dioxide are produced?

Volume-Volume Example

#4

Mole - MoleKnown mol of unknown

mol of known

Mol Ratio – from equationMass - Mass

Known g

molar mass known

1 mol known mol of unknown

mol of known 1 mol unknown

molar mass unknown

Known L

22.4 L known

1 mol known mol of unknown

mol of known 1 mol unknown

22.4 L unknown

particles

6.02 × 1023 particles

6.02 × 1023 particles

OROR

OR

Other

Formulas to Use

Stoichiometry Problems

• How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas?

9 mol O2 2 mol KClO3

3 mol O2

= 6 mol KClO3

2KClO3 2KCl + 3O2

Known: 9 moles O2

Unknown: moles KClO3

Stoichiometry Problems• How many grams of KClO3 are required to produce

9.00 L of O2 at STP?

9.00 LO2

1 molO2

22.4 L O2

= 32.68 g KClO3

2 molKClO3

3 molO2

122 g KClO3

1 molKClO3

2KClO3 2KCl + 3O2

Known: 9.00 L O2

Unknown: g KClO3

Stoichiometry Problems

• How many grams of silver will be formed from 12.0 g copper?

12.0g Cu

1 molCu

64 g Cu

= 40.5 g Ag

Cu + 2AgNO3 2Ag + Cu(NO3)2

Known: 12.0 g Cu Unknown: g Ag

2 molAg

1 molCu

108 g Ag

1 molAg

Stoichiometry Problems

• How many grams of silver will be formed from 12.0 g copper?

12.0g Cu

1 molCu

64 g Cu

= 40.5 g Ag

Cu + 2AgNO3 2Ag + Cu(NO3)2

Known: 12.0 g Cu Unknown: g Ag

2 molAg

1 molCu

108 g Ag

1 molAg

Limiting Reactants/Reagents

• Available Ingredients– 4 slices of bread– 1 jar of peanut butter– 1/2 jar of jelly

Limiting Reactant/Reagents bread

Excess Reactants/Reagents peanut butter and jelly

Limiting Reactants/Reagents

• Limiting Reactant/Reagent– used up in a reaction– determines the amount of product

• Excess Reactant/Reagent– added to ensure that the other reactant is

completely used up– cheaper & easier to recycle

To Determine Limiting Reagents

1. Write a balanced equation.

2. For each reactant, calculate the amount of product formed.

3. Smaller answer indicates:– limiting reactant– actual amount of product

Limiting Reagents79.1 g of zinc react with 0.90 L of HCl. Identify

the limiting and excess reactants. How many liters of hydrogen are formed at STP?

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reagents

79.1g Zn

1 molZn

65g Zn

= 27.26 L H2

1 molH2

1 molZn

22.4 LH2

1 molH2

Zn + 2HCl ZnCl2 + H2

79.1 g ? L0.90 L

Limiting Reagents

0.90L HCl

1 molHCl

22.4

L HCl

= 0.45 L H2

1 molH2

2 molHCL

22.4 LH2

1 molH2

Zn + 2HCl ZnCl2 + H2 79.1 g ? L0.90 L

Limiting Reagents

Zn: 27.26 L H2 HCl: 0.45 L H2

Limiting reagent: HCl

Excess reagent: Zn

Percent Yield

• Percent yield- the ratio of the actual yield to the theoretical yield

• Actual yield- the amount of product formed when a reaction is carried out in the laboratory

• Theoretical yield- the calculated amount of product formed during a reaction (mathematical calculation used to make answer keys)

Percent Yield

100yield ltheoretica

yield actualyield %

calculated on paper

measured in lab

Percent Yield

• When 45.8 g of K2CO3 react with excess HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl.

K2CO3 + 2HCl 2KCl + H2O + CO2 45.8 g ? g

actual: 46.3 g

B. Percent Yield

45.8 gK2CO3

1 molK2CO3

138 gK2CO3

= 49.12g KCl

2 molKCl

1 molK2CO3

74g KCl

1 molKCl

K2CO3 + 2HCl 2KCl + H2O + CO2 45.8 g ? g

actual: 46.3 gTheoretical Yield:

B. Percent Yield

Theoretical Yield = 49.12 g KCl

% Yield =46.3 g

49.12 g 100 = 94.3%

K2CO3 + 2HCl 2KCl + H2O + CO2 45.8 g 49.12 g

actual: 46.3 g