1. Chapter 9 Chemical Quantities

2. In order to avoid waste and to be economic, a chemist has to know how much to make, a doctor must know how much to prescribe, an engineer has to know how much fuel to mix with others, etc., etc., etc...
Questions we answer here in Ch 9? How much can I get? How much do I need?
The engineers who develop airbags have to make sure exactly the right amount of gas is made - no more, no less.

3. Ch 9 is a compilation of Chs 1-8!
must name, balance, g to mol, mol to g…
Notice that for the whole chapter, I’ll give you info on one thing, you’ll give me info on another
but the only place they can meet is the balanced equation, the only language they speak is “molese”

4. 9.1 Information Given by Chemical Equations
The cook is a chemist!
Cooking is: mixing ingredients (reactants) in a recipe (equation) to get a certain amount of food (product)
Importance here? that info in a recipe can be used proportionally
double amts? double product!

5. The chemist is a cook!
A 2:1 mole ratio from a balanced equation is just that - as long as the two substances are in 2:1 number ratio (not mass ratio!) it doesn’t matter how much you use

6. 9.2 Mole-Mole Relationships
Remember!
The most common number ratio in chemistry is the
mole ratio!

7. Example
How many moles of KClO3 must decompose to produce 9 moles of oxygen gas? (The other product is KCl.)
1) As always! First, get a balanced equation!
2KClO3  2KCl + 3O2
2) What is the mol ratio between KClO3 & O2?

8. from balanced equation!
Example (cont’d)
Remember this?
9 mol O2
2 mol KClO3
= 6 mol KClO3
3 mol O2
from balanced equation!
Given

9. Example
When 5 mols sodium react with oxygen gas, how many mols of Na2O are formed?
4Na + O2  2Na2O
5 mol Na
2 mol Na2O
= 2.50 mol Na2O
4 mol Na

10. Example
For this unbalanced equation, how many mols of NO do you need to make 7.5 mol H2O?
NO + H2  N2 + H2O
2NO + 2H2  N2 + 2H2O
it’s a 1:1 ratio!
you need 7.5 mol!

11. Example
For this unbalanced equation, how many mols of SiH4 do you need to use with 4.2 mol NH3?
SiH4 + NH3  Si3N4 + H2
3SiH4 + 4NH3  Si3N4 + 12H2
it’s a 3:4 ratio!
you need 3.15 mol!

12. 9.3 Mass Calculations
The study of the amount of substances consumed/produced = stoichiometry
Remember that chemical equations tell you number ratios, not mass amounts!
Your 3 friends now: 1) balanced chemical equations 2) mole ratios 3) math relationships

13. We’ll start off simple with a problem in which I give you moles of one but you are asked about mass of another…
But remember: the only place they can meet is the balanced equation, the only language they speak is molese

14. CaC2 + 2H2O  C2H2 + Ca(OH)2 Balanced equation!!!
CaC2 and water get together to make acetylene, C2H2, and calcium hydroxide. How many grams of water do you need to make 1.55 mol C2H2?
Balanced equation!!!
CaC2 + 2H2O  C2H2 + Ca(OH)2 g
mol H2O
1.55 mol C2H2

15. Example cont’d mol bridge
They can only talk mole language from the balanced equation!
1.55 mol C2H2
2 mol H2O
18.0 g H2O
1 mol C2H2
1 mol H2O
= 55.8 g H2O
mol bridge

16. Example
How many grams of potassium chlorate (KClO3) must decompose to produce KCl and 1.45 mol oxygen gas?
First! balance the equation!!!
2KClO3  2KCl + 3O2

17. 2KClO3  2KCl + 3O2 g
mol KClO3
1.45 mol

18. Example cont’d mol bridge
They can only talk mol language from the balanced equation!
1.45 mol O2
2 mol KClO3
122.6 g KClO3
3 mol O2
1 mol KClO3
= 119 g KClO3
mol bridge

19. Example
How many moles of copper must react with AgNO3 to produce 5.5 g silver and copper(II) nitrate?
First! balance the equation!!!
Cu + 2AgNO3  2Ag + Cu(NO3)2

20. example cont’d
Cu + 2AgNO3  2Ag + Cu(NO3)2
5.5g
mol Cu
mol Ag

21. Example cont’d mol bridge
They can only talk mol language from the balanced equation!
5.5 g Ag
1 mol Ag
1 mol Cu
107.9 g Ag
2 mol Ag
= mol Cu
mol bridge