Chemistry College Exam

Chem 28 Problem Set 1
Date due: August 26, Tuesday 10:00 am

General Instructions:
- Place answers in 1 long ruled pad paper.
- Show all necessary calculations and proper conversion of units. Final answers should be in proper significant figures
- Box all final answers

1.) In a precipitation reaction, 150.0 mL of 0.200 N NaOH was mixed in 50.0 mL aluminum nitrate solution to precipitate all the Al3+.
a.) What is the normality of Al(NO3)3?
b.) What is the molarity of the solution in 1?
c.) What should be the value of n for Al3+? What should be the value of n for OH-? Explain your answers briefly.

2.) Determine the NaOH titer for phosphoric acid if the phosphoric acid solution is at 0.1 N.

3.) A 0.6334-g sample of impure mercury(II) oxide was dissolved in an unmeasured excess of potassium iodide. Reaction: HgO(s) + 4I- + H­2O  [HgI4]2- + 2OH-
Calculate the percentage of HgO in the sample if titration of the liberated hydroxide required 42.59 mL of 0. 1178 M HCl.

4.) The active ingredient in Antabuse, a drug used for the treatment of chronic alcoholism, is tetraethylthiuram disulfide

The sulfur in a 0.4329-g sample of an Antabuse preparation was oxidized to SO2, which was absorbed in H2O2 to give H2SO4. The acid was titrated with 22.13 mL of 0.03736 M base. Calculate the percentage of active ingredient in the preparation.

5.) The phosphorus in a 0.1969-gram sample was precipitated as the slightly soluble (NH4)3PO4·12MoO3. This precipitate was filtered, washed, and then redissolved in acid. Treatment of the resulting solution with an excess of Pb2+ resulted in the formation of 0.2554 g of PbMoO4. Express the results of this analysis in terms of percent P2O5.

6.) A 6.881 -g sample containing magnesium chloride and sodium chloride was dissolved in sufficient water to give 500 mL of solution. Analysis for the chloride content of a 50.0-mL aliquot resulted in the formation of 0.5923 g of AgCl. The magnesium in a second 50.0-mL aliquot was precipitated as MgNH4PO4; on ignition of this precipitate, 0.1796 g of Mg2P2O7 was found. Calculate the percentage of MgCl2•6H2O and of NaCl in the sample.