South Pasadena • AP Chemistry
Name
1 ▪ Describing Matter
Period
1.1
PROBLEMS
–
Date
CHEMICAL ANALYSIS
Work out the following problems on a separate sheet of paper, showing your work neatly so the steps of your
process can be followed easily. Attach your work to this page.
1. A mixture of CuSO4 and CuSO4 · 5 H2O has a mass of 1.245 g, but, after heating to drive off all the water, the
mass is only 0.832 g. What is the weight percent of CuSO4 · 5 H2O in the mixture? (Ch 4, #32)
2. A 1.25-g sample contains some of the very reactive compound Al(C6H5)3. On treating the compound with
aqueous HCl, 0.951 g of C6H6 is obtained.
Al(C6H5)3 (s) + 3 HCl (aq)  AlCl3 (aq) + 3 C6H6 (ℓ)
Assuming that Al(C6H5)3 was converted completely to products, what is the weight percent of Al(C6H5)3 in
original 1.25-g sample? (Ch 4, #34)
3. Styrene, the building block of polystyrene, is a hydrocarbon, a compound consisting only of C and H. If 0.438
g of styrene is burned in oxygen and produces 1.481 g of CO2 and 0.303 g of H2O, what is the empirical
formula of styrene? (Ch 4, #36)
4. Menthol, from the oil of mint, has a characteristic cool taste. The compound contains only C, H, and O. If
95.6 mg of menthol burns completely in O2, and gives 269 mg of CO2 and 110 mg of H2O, what is the
empirical formula of menthol? (Ch 4, #38)
5. Silicon and hydrogen form a series of compounds with the general formula SixHy. to find the formula of one
of them, a 6.22-g sample of the compound is burned in oxygen. On doing so, all of the Si is converted to
11.64 g of SiO2 and all of the H to 6.980 g of H2O. What is the empirical formula of the silicon compound?
(Ch 4, #40)
6. A compound was analyzed and found to contain 53.30% carbon, 11.19% hydrogen, and 35.51% oxygen by
mass. If the molar mass of the compound is 90.12 g/mol, find the empirical and molecular formulas for this
compound.
7. Tartaric acid is the white, powdery substance that coats tart candies such as Sour Patch Kids. Combustion
analysis of a 12.01 g sample of tartaric acid – which contains only carbon, hydrogen, and oxygen – produced
14.08 g CO2 and 4.32 g H2O.
CxHyOz (s) + O2 (g) → CO2 (g) + H2O (ℓ)
If its molar mass is 150 g/mol, determine the empirical and molecular formulas for tartaric acid.
8. An organic compound was synthesized and found to contain only C, H, N, O, and Cl. It was observed that
when a 0.150-g sample of the compound was burned, it produced 0.138 g of CO2 and 0.0566 g of H2O. All
the nitrogen in a different 0.200-g sample of the compound was converted to NH3, which was found to have a
mass of 0.0238 g. Finally, the chlorine in a 0.125-g sample of the compound was converted to AgCl. The
AgCl, when dried, was found to weigh 0.251 g.
(a) Calculate the percent by mass of each element in the compound.
(b) Determine the empirical formula for the compound.
AP Chemistry 1982 #3
Water is added to 4.267 grams of UF6. The only products are 3.730 grams of a solid containing only uranium,
oxygen, and fluorine and 0.970 gram of a gas. The gas is 95.0 percent fluorine, and the remainder is hydrogen.
(a) From these data, determine the empirical formula of the gas.
(b) What fraction of the fluorine of the original compound is in the solid and what fraction in the gas after the
reaction?
(c) What is the formula of the solid product?
(d) Write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of the
gas is the true formula.