1. Chapter 9 Key Terms
Mole Molar Mass Avogadro's Number Percent Composition Stoichiometry Limiting Reactant Excess Reactant Actual Yield Theoretical Yield Structural Formula Molecular Formula Empirical Formula Percent Yield Law of Definite Composition 1

2. Chemical Calculations
Chapter 9
Chemical Calculations

3. The Mole Used to measure many small items quickly
Defined: the amount of substance contained in x units
When used in equations, we will use 4 significant figures for the mole
Perspective: If you had 1 mole of dollars, how long would it take you to spend all of your money if you spent it at a rate of $1 million per second?

4. The Mole
$6.022 x sec 1 hr 1 day 1 year $1 x s 24 hrs 365 days Over 27 billion years

5. Molar Mass Describes the mass of 1 mole of any pure substance
The mass of 1 mole of any element is shown on the periodic table
1 C atom weighs amu’s
1 mole of C atoms weighs g

6. Molar Mass What is the mass of 1 mole of carbon? 12.011 grams
How many atoms in 1 mole?
6.022 x 1023
What is the mass of ½ mole of carbon
grams
g of carbon contains the same number of atoms as 1 mole of carbon

7. Molar Mass What is the mass of 1 mole of gold? 196.96655 g
How many atoms?
6.022 X 1023
What is the mass of ½ mole of gold? g
g of carbon contains the same number of atoms as g of gold

8. Molar Mass What is the mass of 1 mole of Mg? 24.3050 g
What is the mass of 2 moles of Mg? g
How many atoms in 2 moles?
1.204 x 1024
g of C contains the same number of atoms as g of Au and the same number of atoms as g of Mg

9. Molar Mass Molar mass: the mass of 1 mole of a pure substance in grams
The substance can be a compound or an element
Molar mass of water (H2O)
2 H = 2 mol x g/mol = g
1 O = 1 mol x g/mol = g
g g = g = molar mass of water

10. Molar Mass Calculate the molar masses of the following compounds: HCl
Mg3(PO4)2
Mg(OH)2

11. Types of Formulas Structural formula Molecular Formula
Shows the arrangement of atoms in the compound
Molecular Formula
Shows the types and numbers of atoms involved as they appear in the molecule
Empirical formula
Shows the elements present in the simplest whole-number ratio

12. Percent Composition
Describes the mass composition of a compound by showing what percentage of its total mass comes from each element
Percent composition = part/whole x 100%
A gram sample of water decomposes into 6.72 g H and g O. What is the percent composition of water?
H = 6.72 g / g x 100% = 11.2%
O = g / g x 100% = 88.80%

13. Percent Composition
30.00 g sample of Al2(SO4)3 contained g Al, g S, and g O. What is the percent composition?
4.731 g Al / g = % Al
8.433 g S / g = % S
g O / g = % O

14. Calculations with Empirical Formulas
1 mole of H2O
g/mol = g H
g/mol = g O
Total mass of g H2O
Find percent composition
H = 11.19% O = 88.81%

15. Percent Composition Calculations
Caffeine is made up of 5.170% H, 16.49% O, 28.86% N, and % C by mass. What is the empirical formula for caffeine?
C4H5N2O

16. Stoichiometry
The relationships between the amounts of reactants and products in a chemical reaction
Give mass of a substance and asked for mass of the other reactant for the reaction to fully occur
Give mass of reactants and ask for mass of product
Give mass of both reactants and asked which will run out first
Limiting Reagent: reagent/reactant that runs out or limits the process from continuing
Excess Reagent: reagent/reactant left over after reaction

17. Moles of substance Mass of substance
Moles to Mass
Molar mass
of substance
Moles of substance
Mass of substance
Calculate the number of moles in g of NaOH
26.00 g NaOH mole NaOH
= = mol NaOH
g NaOH

18. Molar Mass Calculate the mass in g if 0.02 moles of NaOH are present
Calculate how many moles of water are present in 10 g
0.02 mol NaOH g NaOH
= = 0.8 g NaOH
1 mole NaOH
10 g H2O mole H2O
= = 0.6 mol H2O
g H2O

19. Moles to Number of Atoms
Number of atoms or molecules
Avogadro’s
Number
Moles of substance
Calculate the number of Na atoms if you have 0.34 moles
0.34 mol Na x 1023 atoms Na
= x 1023 = 2.0 x 1023 atoms Na
1 mol Na

20. Number of atoms or molecules
Stoichiometry
Avogadro’s
Number
Molar mass
of substance
Number of atoms or molecules
Moles of substance
Mass of substance

21. Stoichiometry
Now, we can find out how much of other substances are needed or produced using the chemical equation
Mole ratios
Shows the ratio between the moles of one substance and the moles of another substance in a chemical reaction
2 H2 + O2  2 H2O
P4 + 5 O2  2 P2O5
If someone wanted to produce 25.0 moles of P2O5, how many moles of P4 are needed?

22. Moles of substance 1 Moles of substance 2
Coefficients
Moles of substance 2

23. Stoichiometry
Find the mole to mole ratio of the “ingredients” – shown by the coefficients
1 CH4 + 2 O2  1 CO2 + 2 H2O
Convert based upon what you are given and what you need
Mass to moles
Moles to moles
Moles to mass

24. Mass (grams) Mass (grams) Mole Mole Particles Particles
Molar mass (periodic table)
Molar mass (periodic table)
Mass
(grams)
mole ratio
Mole
Mole
Particles
(atoms,
molecules,
formula units)
Particles
(atoms,
molecules,
formula units)
6.02 x 1023
6.02 x 1023

25. Problems
What mass of water will react with 3550 grams of diphosphorus pentoxide?
P2O5 + 3 H2O 2 H3PO4
Mole ratio = 1:3
Mass to mole, mole to mole, mole to mass

26. Problems
How many grams of NaCl must be decomposed to yield 27 g of chlorine gas?
First write out the balanced equation

27. Problems
2 Na + Cl2 2NaCl
How many grams of sodium chloride are produced from 46 g of sodium and excess chlorine?
How many moles of O2 are produced when 3.00 moles of Al2O3 decompose?

28. Problems
If 56 g of Fe are added to a solution of copper (II) sulfate, how much solid copper will form?
2 Fe + CuSO4 Fe2(SO4)3 + 3 Cu
How many moles of copper can be produced from 446 g Cu2SO4?
Zn + Cu2SO4 ZnSO4 + 2 Cu