ANSWER KEY : % Composition, Hydrate and Empirical & Molecular Formula Problems
Solve the following problems. Show all of your work. Attach extra paper if you need more space.
1. Find the percent composition of a compound containing tin and chlorine if 18.35 grams of the compound contains 5.74 grams of tin.
31.3 % Sn; 68.72 % Cl
2. Calculate the percent composition of tetraphosphorus decoxide.
P4O10: 43.64% P; 56.36% O
3. Calculate the percent composition of magnesium nitrate.
Mg(NO3)2 16.39% Mg; 18.89% N; 64.72% O
4. If magnesium hydroxide is composed of 41.7% Mg, calculate the number of grams of Mg in 185 grams of Mg(OH)2.
77.1 g Mg
5. Which of the following compounds has the highest iron content?
a) FeO b) Fe2O3 c) Fe3O4 A has highest Fe content
a) 77.73% Fe; b) 69.94% Fe; c) 72.36% Fe
7. Calculate the % by mass of water in calcium chloride hexahydrate (CaCl2 . 6H2O)
49.35 % water
8. Calculate the % by mass of water in magnesium sulfate heptahydrate (MgSO4 . 7H20).
9. What is the empirical formula for benzene, C6H6? CH
10. What is the empirical formula for butane, C4H10, commonly used in lighters? C2H5
11. Find the empirical formula of a compound that contains 75% carbon and 25% hydrogen.
12. The most common form of nylon (Nylon-6) is 63.68% C, 12.38% N, 9.80% H and 14.14% O. Calculate the empirical formula for Nylon-6.
13. When a 0.3546 gram sample of vanadium metal is heated in air, it reacts with oxygen to achieve a final mass of 0.6330 gram. Calculate the empirical formula of this vanadium oxide.
14. Find the empirical formula for a hydrate of NiCl2 if it contains 45.4% water.
NiCl2 · 6 H2O
15. Cisplatin, the common name for a platinum compound that is used to treat cancerous tumors, has the composition (mass percent) 65.02% platinum, 9.34% nitrogen, 2.02% hydrogen and 23.63% chlorine. Calculate the empirical formula for cisplatin.
16. What is the molecular formula of the molecule that has an empirical formula of CH2O and a molar mass of 120.12 g/mol?
17. A compound is composed of 34.2% sodium, 17.7% carbon, and 47.6% oxygen. Find its empirical formula. If its molecular mass is 134 g/mol, find its molecular formula.
EF = NaCO2 Mol. F = Na2C2O4
18. A compound used as an additive for gasoline to help prevent engine knock shows the following percentage composition: 71.65% Cl; 24.27% C; and 4.07 % H. The molar mass is known to be 98.96 gram. Determine the empirical formula and the molecular formula for this compound.
EF = CH2Cl Mol F = C2H4Cl2