1. Enjoyed snow day ??? Homework 6 posted and due Monday 3/5
Homework 7 posted and dues this Friday 3/9
Enjoyed snow day ???

2. Chemical Compositions from Combustion Data (continued)
2) A hydrocarbon sample (Cx Hy) is burned in oxygen producing 1.0 gram of CO2 and g H2O. What is the empiric formula for the hydrocarbon ? (C=12, O=16, H=1)
ANSWER: CH2
CxHy CO2 + H2O
mass g g
MW(g/mol)
mol
=mol C 2*0.0227= mol H

3. A hydrocarbon,CxHy burns to form 22 g CO2 and 18 g H2O
A hydrocarbon,CxHy burns to form 22 g CO2 and 18 g H2O. What is the empiric formula of CxHy? CH
CH2
CH3
CH4
None of above

4. A 3 g sample of a copper oxide is heated to drive off oxygen
A 3 g sample of a copper oxide is heated to drive off oxygen. On cooling g of pure Cu remains. What is the copper oxide’s empiric formula ?
CuO2
Cu2O
CuO
CuO3

5. The mole road trip itinerary...
% composition problems
and combustion analysis
(pp )
Reaction balancing
(pp ).
Reaction stoichiometry predictions, limiting yields and % yields:moles level 3 ( pp )

6. Essentially, just try to make elements balance by trial and error
How to Reaction balance (pp )
Essentially, just try to make elements balance by trial and error

7. Chemical bookkeeping: balancing reactions old school (on blackboard)
Example #1:
Element combustion 2 2
Cu +O2  CuO
Balanced !!!! 

8. Reaction balancing (continued)
Example #2:
Organic combustion
Balanced…at last !!!!
C3H8+ O2  CO2+ H2O 5 3 4
Propane=LNG
Liquid Natural Gas
Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

9. 2 16 __C8H18 + __O2 __H2O + __ CO2 25 Internal combustion reaction 18
Slightly trickier balancing…the odd/even oxygen dilemma
Internal combustion reaction 2 16
__C8H18 + __O2 __H2O + __ CO2 25 18
Octane = gasoline
balanced

10. More in-class equation balancing practice4
__H3PO3  ___H3PO4 + ___PH3 3 1
Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

11. More in-class equation balancing practice9
__As2S3 + __O2 __As2O3 + __SO2 2 2 6

12. More in-class equation balancing practice1 4
__H3PO3  ___H3PO4 + ___PH3 3
Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

13. 2 13 12 14
____C6H14 + ___O2  ___CO2 +___H2O
Balance me, please !!!
…On Board
( a trickier one…)

14. The missing coefficient in the reaction: 2C8H18 + __O2 16CO2 + 18H2O50 34 32 25

15. The mole road trip itinerary...
% composition problems
and combustion analysis
(pp )
Reaction balancing
(pp )
necessary prequel to moles level 3
Reaction stoichiometry predictions, limiting yields and % yields: moles level 3 ( pp )

16. Reaction Stoichiometry problems: Moles level 3 how chemists cook
Outline solution on board for each of the 3 samples…

17. Reaction stoichiometry means following…..
THE RECIPE

18. 12 How many boxes of cream to make 4 souffles ? THE RECIPE… 1 + 2 + 3
300 g/block
500 g/dozen
200 g/box
1900 g/souffle
How many boxes of cream to make 4 souffles ? 12

19. 2 1 + 2 + 3 600 grams cheese makes how many souffles ?
Cooking and stoichiometry
THE RECIPE 1 + 2 + 3
300 g/block
500 g/dozen
200 g/box
1900 g/souffle
600 grams cheese makes how many souffles ? 2

20. Cooking and stoichiometry
THE RECIPE 1 + 2 + 3
300 g/block
500 g/dozen
200 g/box
1900 g/souffle
3000 g
How many grams of eggs combine with 9 boxes of cream ?

21. 2 48 eggs combine with how many blocks of cheese? 1 + 2 + 3
Cooking and stoichiometry
THE RECIPE 1 + 2 + 3
300 g/block
500 g/dozen
200 g/box
1900 g/souffle
48 eggs combine with how many blocks of cheese? 2

22. Simple mol-mol stoichiometry conversions
C3H8 + 5O  3CO2 + 4H2O
How many moles of O2 will burn to form 1.2 moles of CO2 ?
Method 1: factor label way
1) given
2) want
* 5 mol O mol CO2
1.2 mol CO2
= ? mol O2 2
3) Use reaction stoichiometry coefficients in right ratio to cancel and connect…which ratio ???

23. Mol-mol stoichiometry conversions (continued)
Method 2: `mole ratios’ way
C3H8 + 5O  3CO2 + 4H2O
1.2 mol
?? m
Problem stated visually
How many moles of O2 will burn to form 1.2 moles of CO2 ?
1) ratio `wanted’ moles in numerator to given in denominator m
1.2 5 3
2) Set equal to matching coefficients for compounds given in reaction…which ??? =
1.2* m= *5
= 2
3)Solve for m

24. More complex stoichiometry problem done 2 ways
MW g/mol
C3H8+ 5O2  3CO2+ 4H2O
22 grams of C3H8 burned with O2 makes how many grams of H2O ?
Method 1: factor label
22 g C3H8 x
1 mole C3H8
44 g C3H8
4 mol H2O
1 mole C3H8 x
18 g H2O
1 mol H2O x
= ?? g H2O 36

25. Method 2: mole ratio way (Board first)
22 grams of C3H8 burned with O2 makes how many grams of H2O ?
g/mol
Given:
Problem
stated
visually
C3H8+ 5O2  3CO H2O
?? g
22 g

26. Method 2: mole ratio way
22 grams of C3H8 burned with O2 makes how many grams of H2O ?
g/mol
Given:
Problem
stated
visually
C3H8+ 5O2  3CO H2O
?? g
22 g
0) convert all given masses & molecule counts to moles
= 0.5 mol C3H8
22 g C3H8 * 1 mol C3H8
44 g C3H8

27. ?? g 22 g = 4 m = mol H2O 1 0.5 mol C3H8 44 32 44 18 g/mol Given:
Method 2: mole ratio way
22 grams of C3H8 burned with O2 makes how many grams of H2O ?
g/mol
Given:
C3H8+ 5O2  3CO H2O
Problem
stated
visually
?? g
22 g
= 0.5 mol C3H8
1) ratio `wanted’ moles m in numerator to given in denominator:
= 4 1
m = mol H2O
0.5 mol C3H8

28. ?? g 22 g 2) Solve for wanted moles m 0.5 1 0.5 * *0.5 = 2 mol H2O
Method 2: mole ratio way
22 grams of C3H8 burned with O2 makes how many grams of H2O ?
g/mol
Given:
C3H8+ 5O2  3CO H2O
?? g
22 g
2) Solve for wanted moles m
0.5
= 4 1
0.5 *
*0.5
= 2 mol H2O

29. Method 2: mole ratio way
22 grams of C3H8 burned with O2 makes how many grams of H2O ?
g/mol
Given:
C3H8+ 5O2  3CO H2O
?? g
22 g
= 2 mol H2O
3) Convert wanted moles to wanted final units (grams)
2 mol H2O * g H2O
1 mole H2O
= 36 g H2O

30. Practicing…clickers and not clickers

31. c)wtwt: How many grams of O2 are needed to burn 1.1 g C3H8?
C3H8 + 5O  3CO2 + 4H2O (BOOM)
g/mol
c)wtwt: How many grams of O2 are needed to burn 1.1 g C3H8?
0.8
4.0
0.25
0.16

32. C3H8 + 5O2-------- 3CO2 + 4H2O (BOOM)
g/mol
e) count wt: How many grams of O2 are needed to form 9*1022 molecules of H2O ? count wt
1.0 g
2.0 g
1.5 g
6.0 g

33. 3 mol H2O C3H8 + 5O2-------- 3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol
weight to moles
How many moles of H2O form if 33 g of C3H8 are burned ?
3 mol H2O

34. =4*1022 How many molecules of CO2 form if 1.592 g H2O results ?
C3H8 + 5O  3CO2 + 4H2O (BOOM)
g/mol
f) weight to count
How many molecules of CO2 form if g H2O results ?
=4*1022

35. C3H8 + 5O2-------- 3CO2 + 4H2O (BOOM)
g/mol
Mol count: How many molecules of O2 does it take to form moles of CO2 in the reaction above? (1 mol count=6*1023)
1.2*1022
7.2*1021
1.0*1022
2.0*1022

36. C3H8 + 5O  3CO2 + 4H2O
g/mol wtcount
How many molecules of CO2 are formed along with 0.40 g H2O in the reaction above. (1 mol count =6*1023)
1.33*1022
1*1022
7.5*1021
4*1022