1. Stoichiometry

2. Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions.
It could be amounts of substances before the reaction or amount of material that is produced by the reaction.
Stoichiometry is all about amounts.

3. What a balanced chemical equation tells us
A chemical equation represents the mole ratio of reactants and products
CuCl2 + 2AgNO3  2AgCl + Cu(NO3)2
1mol mol mol mol
NaOH + HCl  NaCl + H2O
1mol mol mol 1mol
2CO + O2 -> 2CO2
2mol mol 2mol
Mg + 2HCl -> MgCl2 + H2
1 mol 2 mol 1 mol mol

4. Stoichiometry will tell you that if you have ten million atoms of sodium (Na) and only one atom of chlorine (Cl) you can only make one molecule of sodium chloride (NaCl). Nothing you can do will change that. Like this:
10,000,000 Na + 1 Cl --> NaCl + 9,999,999 Na

5. Limiting reagent A reagent is another word for reactant
A reaction will stop when one reactant is used up before the other
This is called a limiting reagent
The other reactant is the excess reagent
Blue is the limiting reagent
Red is the excess reagent

6. Limiting reagent
2H2 + O2  2H2O Initial mol Reaction mol Final mol 0 2 8

7. Mass-Mass stoichemtry
Involves solving a problem in which the mass of a reactant or a product is given

8. Calculating the mass of a substance given the mass of another reactant or product
Write a balanced chemical equation
Identify known and unknown quantities of substances
Calculate the number of moles of known quantities
Find the molar ratio and use this to calculate the number of moles of a required substance
Mol of required substance = Molar ratio
Mol of given substance
5. Calculate the quantity o the required, unknown, substance

9. Calculations
Calculate the number of moles of CO2 formed in the combustion of ethane C2H6 in a process when 35.0 mol of O2 is consumed. The reaction is:
2 C2H6 + 7 O2  4 CO2 + 6 H2O
4 CO2 : 7 O2
35.0 mol O2 x 4 CO2 mol = 20.0 mol CO2
7 mol O2 mol

10. Two moles of Mg and five moles of O2 are placed in a reaction vessel, and then the Mg is ignited according to the reaction Mg + O2  MgO.
Identify the limiting reagent in this experiment.
2 Mg + O2  2 MgO
2 mol 1mol (I have 5, 5 -1 = 4 mol unused)
Four moles of oxygen will remain unreacted.
Oxygen is the excess reagent, and Mg is the limiting reagent.

11. What mass of iron (III) oxide is formed from the complete combustion of 183.5g of pyites (FeS2)
FeS2 + O2 Fe2O3 + SO2
4FeS2 + 11O2 2Fe2O3 + 8SO2
molar mass of FeS2 = (2 x 32.1)
= g/mol
= 183.5g x 1 mol
120.05g
= mol

12. 3. Find the molar ratio of 4FeS2 to 2Fe2O3 4:2 2:1
4:2 2:1
Mol of Fe2O3 = 2 FeS2 = 1
= mol 2
Mol of Fe2O3 = mol
4. Molar mass of Fe2O3 = 2 x x 16
= g/mol
mol x 159.7g
1mol
= 122.1g of Fe2O3

13. Calculate the mass of water produced when 2
Calculate the mass of water produced when 2.8g of CH4 is burnt in the air
CH4 + 2O2  2H2O + CO2
Molar mass = = 16g/mol
Mol of CH4 = 2.8g x 1 mol
16g
Mol of CH4 = mol
3. Molar ratio
CH4 : H2O 1:2
CH4 = 1 = mol = mol of H2O
H2O
4. Molar mass of H20 = 2+16 = 18g/mol
Mass of H20 = mol x 18g = 1.575g
1 mol

14. Limiting reagent
How much precipitate can you make with only 2.6mol of KCl?
AgNO3 + KCl 
AgNO3(aq) + KCl(aq)  AgCl (s) + KNO3(aq)
2.6mol
KCL is the limiting reagent we only have a certain amount of it

15. Balance equation
AgNO3(aq) + KCl(aq)  AgCl (s) + KNO3(aq)
Determine molar ratio
KCl to AgCl is 1:1
I have 2.6mol of KCl I have 2.6 mol of AgCl
Molar mass of AgCl = g/mol
2.6mol KCl x 1mol of AgCl x g of AgCl
1 mol of KCL mol of AgCl
= g of AgCl

16. If 6.3g of S8 react with Pb, how many grams of PbS are formed?
Pb + S8  PbS
8Pb + S8  8PbS
6.3g ?
Molar mass of S8 = x 8 = g/mol
Mol of S8 = 6.6g x 1mol
256.48g
= mol
Molar ratio = PbS 8 S
Mol of PbS = 8 x = mol
Molar mass of PbS = g/mol
Mass of PbS = 1.647mol x g
1 mol
= g

17. Determine the limiting reagent
What mass of liquid water is formed when 2.3g of H2 gas and 4.55g of O2 gas react together
2H2 + O2  2H2O
2.3g g
Molar mass of H2 = 2g/mol
Mol of H2 = 2.3g x 1mol = 1.15mol 2g
Molar mass of 02 = 32g/mol
Mol of O2 = 4.55 x 1 mol = 0.142mol
32g

18. 2H2 + O2  2H2O x 2 = 0.284mol of H2 Which is the limiting reagent? 02 2H2 + O2  2H2O Molar mass of H2O = 18g/mol Mass of H2O = 0.282mol x 18g 1 mol = 5.076g

19. What volume of 0. 100mol/L H2SO4 acid reacts completely with 17
What volume of 0.100mol/L H2SO4 acid reacts completely with 17.8mL of 0.15 of potassium hydroxide?
Molar ratio = H2SO4 1
KOH
Mol of H2SO4 = ½ x mol
L of H2SO4 = mol x 1L
0.1mol
L of H2SO4 = L
Acid + base  salt + water
KOH H2SO4  K2SO4 + H20
2KOH H2SO4  K2SO4 + 2H20
0.15M M
17.8mL ?
(0.0178L)
Mol of KOH = L x 0.15mol 1L
= mol

20. Zinc metal is reacted with 400mL of a 0
Zinc metal is reacted with 400mL of a 0.25mol/L solution of sulfuric acid. Calculate the mass of zinc sulfate formed

21. Questions
Pg 263 Q 1, 2, 4, 6,7,8
Pg 267 Q 9

22. Titration
A titration is a method of analysis that will allow you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration flask. A buret is used to deliver the second reactant to the flask and an indicator or pH Meter is used to detect the endpoint of the reaction.

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