Sample Solution of Homework 5

							CHEM 121 Fall 2008 HOMEWORK 5 NAME:
10 pts
Due 1 Oct 2008, Wed, 9:00 AM
INCOMPLETE HOMEWORK MAY EARN ZERO POINTS.
Your homework has to be clear, well organized, and legible.

Use atomic masses as listed in “our” periodic table.

1. A sample of phosphorus weighing 0.500 g was ignited in oxygen gas to produce phosphorus
oxide. The product, phosphorus oxide, had a mass of 1.145 g. The molar mass of the phosphorus
oxide was 285 g/mol. What is the empirical and molecular formula of the phosphorus oxide? What
is the correct name of this compound? Show all calculations.

2. A 1.000 g sample of an alcohol (contains C, H and O) was analyzed by combustion and produced
1.913 g CO2 and 1.174 g H2O. The molar mass is 46 g/mol. What is the empirical and molecular
formula of the alcohol? Show all calculations.

3. How many grams of sodium sulfate are in 230. mL of a 0.455 M sodium sulfate solution? Show
all calculations. Use sig figs correctly.

4. How many milliliters of a 0.500 M sodium sulfate solution contain 17.5 g of sodium sulfate?
Show all calculations. Use sig figs correctly.

5. 12.45 g of sodium sulfate was dissolved in 500.0 mL of solution. What is the molarity of the
solution? Show all calculations. Use sig figs correctly.

6. 11.0 mL of 1.10 M HBr reacts with 0.345 g of Ca(OH)2. If the percent yield is 80.0% in this acid-
base neutralization, how many g of CaBr2 are produced? Write the balanced equation. Determine
the limiting reactant. Show all calculations. Use sig figs correctly.
        2 HBr + Ca(OH)2 --> CaBr2 + 2 H2O

7. In an acid-base titration, 15.87 mL of 0.3450 M KOH is used to titrate 20.05 mL of phosphoric
acid. What is the molarity of the acid? Show all calculations. Use sig figs correctly.
        3 KOH + H3PO4 --> K3PO4 + 3 H2O