NAME:_________________________
DATE:__________
PER:_________
Determining Molecular Weight / Molar Masses – Notes and Practice WS
Step one – Identify the molecular formula
Ex calcium fluoride is CaF2
Step Two – Determine the number of atoms of each element
1 Ca
2F
Step Three – Multiply the number of atoms by the atomic weights and total them.
1 Ca x 40.1
2 F x 19
=
=
40.1
38
78.1
grams
grams
Solve the following on a lined paper: SHOW ALL WORK!
1.
NH4Cl
2.PbCl2
3.
Li2SO4
4.CuSO4
5.
KMnO4
6.KClO3
7.
AgNO3
8. H2O2
9.
As2P5
10. CuCl2
Solve the odds on lined paper: SHOW ALL WORK!
11.
Aluminum sulfate
12. Ammonium nitrate
13.
Barium hydroxide
14. Calcium acetate
15.
Carbon dioxide
16. Magnesium chromate
17.
Mercury(I) chlorite
18. Potassium permanganate
19.
Silver phosphate
20. Ferric carbonate (iron(III) carbonate)
Key for 1-12: (1) 51.5 g/mol (2) 279 g/mol (3) 110 g/mol (4) 159.5 g/mol (5) 158 g/mol (6) 122.5 g/mol
(7) 170 g/mol (8) 34 g/mol (9) 305 g/mol (10) 134.5 g/mol (11) 342.14 g/mol (12) 80 g/mol
Page 1 of 2
NAME:_________________________
DATE:__________
PER:_________
Determining Percent Composition – Notes and Practice
Percent Composition By Atomic Masses.
Step one – Identify the molecular formula
Ex. calcium fluoride is CaF2
Step Two – Determine the number of atoms of each element
1 Ca
2F
Step Three – Multiply the number of atoms by the atomic weights of each element and total them.
1 Ca x 40.1 =
40.1 grams
2 F x 19
=
38
grams
78.1
Total (This is the molecular weight of CaF2)
Step Four -- Divide the weight of the individual elements by the total weight (Total from step 3) then
multiply it by 100.
1 Ca x 40.1 =
40.1 grams / 78.1 = .513 x 100 = 51.3 %
2 F x 19
=
38
grams / 78.1 = .487 x 100 = 48.7 %
78.1
100.0%
Answer Check
NOTE: To check you answer: The total percent should add up to 99.9, 100.0 or 100.1 percent
Solve any the following on a lined paper: SHOW ALL WORK!
1. NH4Cl
2.
PbCl2
3. Li2SO4
4.
CuSO4
5. KMnO4
6.
KClO3
7. AgNO3
8.
H2O2
9. As2P5
10.
CuCl2
Solve the odds on lined paper: SHOW ALL WORK!
11. NaC2H3O2
12.
H3OBr
13. Ag2CrO4
14.
Fe3(PO4)2
15. CoSO3
16.
Hg2S
17. Ba(OH)2
18.
CaO2
19. Fe2O3
20.
Sn(OH)4
Percent Composition Key for 1 - 10
1. NH4Cl
N = 26.2%
H = 7.5%
Cl = 66.3%
3. Li2SO4
Li = 12.6% S = 29.2%
O = 58.2%
5. KMnO4 K = 24.7% Mn = 34.7%
O = 40.5%
7. AgNO3 Ag = 63.5% N = 8.2%
O = 28.3%
9. As2P5
As = 49.1% P = 50.9%
2. PbCl2
4. CuSO4
6 KClO3
8. H2O2
10. CuCl2
Pb = 74.5%
Cu = 39.8%
K = 31.9%
H = 5.9%
Cu = 47.2%
Cl = 25.5%
S = 20.1% O = 40.1%
Cl = 29%
O = 39.1%
O = 94.1%
Cl = 52.8%
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