1. Homework 6 posted and due Monday 3/5
Sigh, another Monday…

2. The road trip through mole land so far…
Basic mole-mass-count
conversions ( divide up,
multiply down):
=Moles level 1
Mole ratio conversion within
a compound (`body parts’ relationships)
= Moles level 2

3. The mole road ahead... % composition problems and combustion analysis
(pp ) :
moles level 2b
Reaction balancing
(pp ): necessary prequel to moles level 3
Reaction stoichiometry predictions, limiting yields and % yields ( pp ): moles level 3

4. Why bother with all of this ????

5. % composition problems: using mole concept to convert weights to formulas
Sample % composition problem #1
A compound of N and O contains wt % N and wt % O. What is the empiric formula of the compound ?

6. Example: CH2O = empiric formula of glucose (sugar we metabolize)
Definition:
empiric formula= mole ratio of elements in a compound expressed in lowest whole numbers
Example: CH2O = empiric formula of glucose (sugar we metabolize)

7. C6H12O6= (CH2O)6 Sugar =Carbo hydrate
Empiric formulas (continued)
CH2O = empiric formula of glucose (sugar we metabolize)
Actual molecular formula (what it really has in atom count):
C6H12O6=
(CH2O)6
Sugar =Carbo hydrate

8. C3H6O3 CH2O ÷ 3 NOT EMPIRIC EMPIRIC Which formulas below are empiric
(= lowest common denominator form) ??
÷ 3
NOT EMPIRIC
EMPIRIC
C3H6O3
CH2O

9. N3F7 EMPIRIC…3 & 7 have no shared factors
Which formulas below are empiric (continued) ??
EMPIRIC…3 & 7 have no shared factors
N3F7

10. H3P9O12S5 EMPIRIC Which formulas below are empiric (continued) ??
(3,9,12 divisible by 3…but 5 is not)

11. Which compound in the list is not empiric: NO2 , N2O3 ,N3O9 , N2O

12. % composition Problem 1: empiric formula determination
A compound of N and O contains 63.63% N and %O. What is the empiric formula of the compound?
let’s do it on the board…using the `table’ method

13. OFFICIAL NAME… Dinitrogen monoxide =>N2O =Laughing gas
Sample problem #1; SUMMARIZED
OFFICIAL NAME…
Dinitrogen monoxide
=>N2O
=Laughing gas n
nmin
element N O
AW=Atomic wt (g/mol)
n=w/AW
moles
w(g)
4.545 = 2
2.273
63.63/14=
4.545
63.63 14
36.36/16= 2.273
2.273 =1
2.273
36.36 16

14. Joseph Priestley
1772

15. % composition problem 2: An oxide of nitrogen contains 46. 7 wt
% composition problem 2: An oxide of nitrogen contains 46.7 wt. % N and 53.3 % O. What is it’s empiric formula ?
NO3
NO2
N2O
N3O7 NO
None of the above

16. % composition Problem 3:
empiric formula determination with a twist
A compound composed of C,H and O is 48.64% C and 8.16 % H and 43.2 % O by mass. What is the empiric formula ?
Answer: C1.5H3O1 C3H6O2
element
Mass,g
Atomic wt(g/mol)
n=mass Atomic wt
n/nmin C
48.64 12 H
8.16 1 O
43.2 16
x FACTOR
1.5*2= 3
48.64/12=
4.05
4.05/2.7
=1.5 ?
8.16/1=
8.16
3.0*2= 6
8.16/2.7
=3.0
43.2/16=
2.70
2.7/2.7= 1
1*2= 3

17. Compound X is composed of 39. 34 wt % C, 8. 20 wt% H and 52. 56 wt% O
Compound X is composed of wt % C, 8.20 wt% H and wt% O. What is compound X’s empiric formula ?
C4H8O5
CH2O
C2H5O2
CH3O

18. Naughty Kitty Group Project (% composition problem 5)
Using the % composition data for your team:
Determine the compound on your assigned
kitty’s anatomical parts
2) Decide what your kitty’s naughty act was.

19. Tigger
Socks
Bosco
Buddy
Socks

20. Naughty Kitty C H N O anatomical site
Table 1: Percent Composition Data of the Compounds Found on my 4 Naughty Kitties
Naughty Kitty C H N O anatomical site
Bosco paws and tail
Buddy whiskers, saliva, urine
Socks paws
paws
Tigger tail
paws. nose
Note: C=12 H=1 N=14 O=16 (atomic masses)

21. Table 2: Possible Compounds
Identity Molecular formula Notes
Aspirin C9H8O4 Over-the-counter pain killer
Codeine C­18H21NO4 Over-the-counter pain killer
Aspartame C­14H18N2O5 Artificial sweetener
Urea CH4N2O component in urine
Vanilla C8H8O3 Flavoring in cakes, pies, cookies
Theobromine C7H8N4O2 Chocolate flavoring

22. Examining Buddy’s whiskers, saliva and urine sample
C14H18N2O5
=Aspartame (artificial sweetener)
element
Mass=w AW
(g/mol) C
57.14 12 H
6.16 1 N
9.52 14 O
27.18 16
n=mol
=w/AW
n/nmin
X 2
4.76 7 14 18 2 5
6.16 9
0.68 1
2.5 ?
1.698

23. Whiskers etc. => asparatame Paws, tail => urea
Buddy
Bosco
Whiskers etc. => asparatame
Paws, tail => urea
Took my diet cookies
Peed on the living room floor

24. Tigger
Socks
Paws => vanilla
Paws => chocolate
Tail => aspirin
Paws/nose=> codeine
Walked on kitchen counter and cake mix
Made mess in bathroom

25. Let’s do this on the board…
One more twist on composition problems…
empiric  molecular formula determination
The empiric compound (C2H4O3) has a molecular weight of 228 g/mol. What is the molecular formula of the compound ?
Let’s do this on the board…

26. Burn, Baby, Burn !

27. Chemical Compositions from Combustion Data
1) A 0.30 gram sample of carbon black is burned in a covered crucible. The collected gas weighs 0.70 grams. What is the empiric formula of the gas ?(C =12, O =16) 
ANSWER: CO

28. 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