Chapter 7 (pp234-248)
Empirical formulas, hydrated compounds,
Molecular formulas & Percent composition
Name ____________________________________
Period ____________
1. A compound is found to contain 40.00% carbon; 6.67% hydrogen; and 53.55% oxygen. Find its
empirical formula, CxHyOz.
2.
One oxide of iron is called "magnetite." It is composed of 72.4% Fe and 27.6% oxygen. What is the
empirical formula of magnetite, FexOy?
3. Chromium forms several different compounds when it combines with oxygen. From the following data,
calculate the empirical formula for each oxide, CrxOy:
a. 0.765 g Cr and 0.235 g O
b. 5.60 g Cr and 2.62 g O
4. A 4.725 g sample of product was produced when 2.975 g of tin, Sn, were dissolved in hydrochloric acid,
HCl. Calculate the simplest formula for the chloride, SnxCly.
5. When 1.35 g of a silver oxide is decomposed, 1.26 g of silver, Ag, remain. Calculate the simplest
formula, AgxOy.
6. Borax powder has the formula Na2B4O7• X H2O. When 2.145 g of the hydrate is heated and the water is
removed, only 1.130 g of anhydrous salt are left. What is the empirical formula of borax?
7. Calcium sulfate hydrate, CaSO4 • X H2O, contains 20.93% water. Calculate X for the hydrate.
8. If 1.687 g of epsom salt, MgSO4• X H2O is heated to remove all water, 0.824 g of salt remain. What is
the empirical formula of epsom salt?
9. Calculate the % H2O in the compound NiCl2• 6 H2O.
10. Nicotine is the primary active ingredient in various forms of tobacco products. Its formula is C10H14N2.
What is its percent composition of each of its elements?
11. Sodium lauryl sulfate is the major detergent in many shampoos. Its formula is CH3(CH2)11OSO3Na.
What is the percent composition of carbon?
12. Adenine is a component of DNA and RNA. Its composition is 44.44% carbon, 3.73% hydrogen, and
51.83% nitrogen; its formula mass is 135.13 g/mol. What is its molecular formula?
13. Cyclohexane is 85.63% carbon and 14.37% hydrogen and has a formula mass of 84.16 g/mol. What is
its molecular formula
14. Determine the molecular formula for a substance with an empirical formula of C4H4O and a molar mass
of 136 grams per mole.