Everything Conversions - Key
1. What is the molecular formula of a substance with an empirical formula of C3H4O3 and a formula mass of 176?
3(12.0) + 4(1.01) + 3(16.0)= 88.0
176.0 = 2.0
88.0
Molecular formula = 2 * C3H4O3 or C6H8O6
2. Calculate the number of molecules of NBr3 in 37.5 g NBr3.
37.5g NBr3
1
x
1 mole
x
254g NBr3
6.02 x 1023 molecules NBr3 = 8.89 x1022 molecules NBr3
1 mole
3. How many moles are in 14.0g of N2?
14.0g N2 x 1 mole = 0.500 moles N2
1
28.0g N2
4. What is the percent composition of each of the elements in CH3COOH?
Carbon = 2 x 12.0 g = 24.0 g
Hydrogen = 4 x 1.01 = 4.04 g
Oxygen = 2 x 16.0 = 32. 0 g
formula mass is 60.0
Carbon: (24.0 g / 60.0 g) x 100 = 40.0%
Hydrogen: (4.04 g / 60.0 g) x 100 = 6.73 %
Oxygen: (32.0 g / 60.0 g) x 100 = 53.3%
5. Benzoic acid contains 68.8% carbon, 4.95% hydrogen, 26.2% oxygen. What is the empirical formula for
benzoic acid?
68.8g C
1
x 1 mole C
12.0 g
= 5.73moles C
5.73/1.64 = 3.49 (Multiply by 2) = 7
4.95g H
1
x 1 mole H
1.01 g H
= 4.90 moles H
4.90/1.64 = 2.99 (Multiply by 2) = 6
26.2g O
1
x 1 mole O
16. 0g O
= 1.64 moles O
1.64/1.64 = 1(Multiply by 2) = 2
Empirical formula is: C7H6O2
6. Convert 0.877moles RbI to molecules.
0.877 moles RBI x 6.02 x 1023 molecules RbI = 5.28 x 1023 molecules RBI
1
1 mole
7. What is the molecular formula of a substance with an empirical formula of HgF and a formula
mass of 4.40x102? (440 with zero being SD)
201 + 19.0 = (2.20 x102) or 220 (knowing zero is SD)
4.40 x102 = 2.00
2.20x102
Molecular formula = Hg2F2
8. How many grams of copper sulfide make up 3.71 x1025 atoms of copper sulfide?
3.71 x 1025 atoms CuS x
1 mole
x 95.6g CuS
= 5891.6 g CuF  5890g CuF
1
6.02 x 1023 atoms CuS
1 mole
9. A compound consists of 40.0% calcium, 12.0% carbon, and 48.0% oxygen by mass. What is the
empirical formula?
40.1 Ca
1
x
12.0g C
1
x 1 mole C
12.0 g C
48.0 O
1
1 mole Ca
40.0 g Ca
x 1 mole O
16.0 g O
= 1.00 mole Ca
= 1.00 moles C
= 3.0 moles O
1.00/1.00 = 1
1.00/1.00 = 1
3.00/100 = 3
Empirical formula = Ca(CO3)
10. Convert 9.51 x1021 ions As to grams.
9.51 x 1021 ions As x
1 mole
1
6.02 x 1023 ions As
x
74.9g As = 1.18g As
1 mole
11. Determine the empirical formula of a compound that is 78.5% Cs, 12.5% O.
78.5g Cs x 1 mole = 0.590 moles Cs
1
133 g Cs
0.590/0.590 = 1(*3) = 3
12.5g O x 1 mole
= 0.781 moles O
1
16.0 g O
Empirical formula = Cs3O4
0.781/0.590 = 1.23 (*3) =47
12. What is the molecular formula of the compound in #11 if it’s molecular mass is 926g?
926/ 463 = 2
Molecular formula is: Cs6O8
13. What is the percent composition of each of the elements in the compound Iron (III) Sulfide?
Fe2S3
55.8 (2) = 53.8%
32.1 (3) = 46.3%
208
208
14. Convert 86.0g of H2S to molecules.
86.0 g H2S x 1 mole
x 6.02 x 1023 molecules H2S = 1.52 x 1024 molecules H2S
34.1 g H2S
1 mole
15. What is the empirical formula of a compound if a sample contains 7.22g Nickel, 2.53 g
Phosphorus and 5.25g of Oxygen?
7.22 g Ni x 1 moleNi = 0.123 mol Ni
1
58.7g Ni
0.123/0.0816 = 1.5 (*2)= 3
2.53g P x 1 mole P = 0.0816 mol P
1
31.0g P
0.0816/0.0816 = 1 (*2)= 2
5.25g O x 1 mole O = 0.328 mol O
1
16.0g O
0.328/0.0816 = 4(*2) = 8
Empirical formula = Ni3P2O8 or Ni3(PO4)2
16. How many molecules are in 5.62 moles of water?
5.62 moles H2O x 6.02 x 1023 molecules H2O = 3.38 x 1024 molecules H2O
1
1 mole H2O