97.  What weight of metallic copper will be deposited from a cupric salt solution by a current of 1.5 amperes during a period of 45 minutes, assuming 100% current efficiency? (1 Faraday = 96,500 coulombs.)

!Answer!:  1.335 grams.

98.  In the electrolysis of a 0.8000 gram sample of brass, there is obtained 0.0030 gram of PbO_{2}, and a deposit of metallic copper exactly equal in weight to the ignited precipitate of Zn_{2}P_{2}O_{7} subsequently obtained from the solution.  What is the percentage composition of the brass?

!Answers!:  69.75% Cu; 29.92% Zn; 0.33% Pb.

99.  A sample of brass (68.90% Cu; 1.10% Pb and 30.00% Zn) weighing 0.9400 gram is dissolved in nitric acid.  The lead is determined by weighing as PbSO_{4}, the copper by electrolysis and the zinc by precipitation with (NH_{4})_{2}HPO_{4} in a neutral solution.

(a) Calculate the cubic centimeters of nitric acid (sp. gr. 1.42 containing 69.90% HNO_{3} by weight) required to just dissolve the brass, assuming reduction to no.

!Answer!:  2.48 cc.

(b) Calculate the cubic centimeters of sulphuric acid (sp. gr. 1.84 containing 94% H_{2}so_{4} by weight) to displace the nitric acid.

!Answer!:  0.83 cc.

(c) Calculate the weight of PbSO_{4}.

!Answer!:  0.0152 gram.

(d) The clean electrode weighs 10.9640 grams.  Calculate the weight after the copper has been deposited.

!Answer!:  11.6116 grams.

(e) Calculate the grams of (NH_{4})_{2}HPO_{4} required to precipitate the zinc as ZnNH_{4}Po_{4}.

!Answer!:  0.5705 gram.

(f) Calculate the weight of ignited Zn_{2}P_{2}O_{7}.

!Answer!:  0.6573 gram.

100.  If in the analysis of a brass containing 28.00% zinc an error is made in weighing a 2.5 gram portion by which 0.001 gram too much is weighed out, what percentage error in the zinc determination would result?  What volume of a solution of sodium hydrogen phosphate, containing 90 grams of Na_{2}HPO_{4}.12H_{2}O per liter, would be required to precipitate the zinc as ZnNH_{4}Po_{4} and what weight of precipitate would be obtained?

!Answers!:  (a) 0.04% error; (b) 39.97 cc.; (c) 1.909 grams.

101.  A sample of magnesium carbonate, contaminated with SiO_{2} as its only impurity, weighs 0.5000 gram and loses 0.1000 gram on ignition.  What volume of disodium phosphate solution (containing 90 grams Na_{2}HPO_{4}.12H_{2}O per liter) will be required to precipitate the magnesium as magnesium ammonium phosphate?

!Answer!:  9.07 cc.

102. 2.62 cubic centimeters of nitric acid (sp. gr. 1.42 containing 69.80% HNO_{2} by weight) are required to just dissolve a sample of brass containing 69.27% Cu; 0.05% Pb; 0.07% Fe; and 30.61% Zn.  Assuming the acid used as oxidizing agent was reduced to no in every case, calculate the weight of the brass and the cubic centimeters of acid used as acid.