1. Warm-up March 22nd
9.67 moles of KCl = __________________ grams KCl
3.4 x 1032 molecules of NO2 = ____________ grams NO2
52.22 grams of CO=________________L CO at STP

2. Percentage Composition
Percent Composition- the percentage by mass of each element in a compound

3. Percentage Composition
Find the % composition of Cu2S.
g Cu
g Cu2S
%Cu =
 100 =
79.852% Cu
32.07 g S
g Cu2S
%S =
 100 =
20.15% S

4. Percentage Composition
Find the percentage composition of a sample that is 28 g Fe and 8.0 g O.
%Fe = g
36 g
 100 =
78% Fe
%O = g
36 g
 100 =
22% O

5. Percentage Composition
Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O?
36.04 g g
%H2O =
 100 =
24.51%
H2O

6. What is the percent composition of each element in Copper (II) Phosphate

7. Find the percent composition of each element in:
Warm-up
Find the percent composition of each element in:
Fe(NO3)3
K2SO4

8. Warm-up March 22nd Convert 4.5 g CO2 = _________ mol CO2
460 L CO = _________ g CO
1.56 x molecules NO = ______ L NO

9. C2H6 CH3 Empirical Formula
Empirical Formula- Smallest whole number ratio of atoms in a compound
C2H6
reduce subscripts
CH3

10. To Find Empirical Formula
1. Find mass (or %) of each element.
2. Find moles of each element.
3. Divide moles by the smallest # to find subscripts.
4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

11. Empirical Formula
Qualitative analysis shows that a compound contains 32.38% Na, 22.65%S, and 44.99%O. Find the empirical formula of this compound.
32.38 g Na x 1 mol Na = mol Na =
22.99 g Na
22.65 g S x 1 mol S = mol S = 1
32.07 g S
44.99 g O x 1 mol O = mol O =
16.00 g O

12. Empirical Formula
Empirical Formula
Na2SO4

13. Empirical Formula
Find the empirical formula for a sample of 25.9% N and 74.1% O.
25.9 g N x 1 mol N = mol N = 1 N
14.01 g N mol
74.1 g O x 1 mole O = mol O = 2.5 mol O
16.00 g O mol

14. N2O5 N1O2.5 Empirical Formula
Need to make the subscripts whole numbers
 multiply by 2
N2O5

15. Warm-up November 7th Solve each: 3.45 moles CO = _________ g CO
45.6 Liters NO2 = __________ molecules NO2
Calculate the percent composition of each element in Al(NO2)2

16. CH3 C2H6 Molecular Formula ?
Molecular Formula- “True Formula”, the actual number of atoms in a compound
CH3
empirical
formula ?
C2H6
molecular
formula

17. Calculating Molecular Formula
1. Find the empirical formula.
2. Find the empirical formula mass.
3. Divide the molecular mass by the empirical mass.
4. Multiply each subscript by the answer from step 3.

18. Calculating Molecular Formula
The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol?
Empirical formula mass = g/mol
28.1 g/mol
14.03 g/mol
MF = EF
= 2.00
(CH2)2  C2H4

19. Calculating Molecular Formula
If 4.04 g of N combine with g O to produce a compound with a formula mass of amu, what is the molecular formula of this compound?
!st you must find the Empirical Formula
4.04 g N x 1mol N = mol N = 1
14.01 g N
11.46 g O x 1 mol O = mol O
16.00 g O

20. Calculating Molecular Formula
Empirical Formula (N1O2.5)2 = N2O5
N= MF mass = = 1
EF mass
(EF)n = (N2O5)1

21. Calculating Molecular Formula
The Molar mass of a compound is 92 g/mol. Analysis of a sample of the compound indicates that is contains g N and g O. Find its molecular formula.
.606 g N x 1 mol N = mol N = 1
14.01 g N
1.390 g O x 1 mol O = mol O = 1.993
16.00 O

22. Calculating Molecular Formula
Empirical formula = NO2
MF mass = = 2
EF mass 46
(NO2)2 = N2O4