!Answers!:  2.26 cc.; 0.2154 gram.

80.  What volume of nitric acid (sp. gr. 1.05 containing 9.0% HNO_{3} by weight) is required to oxidize the iron in one gram of FeSO_{4}.7H_{2}O in the presence of sulphuric acid? 6FeSO_{4} + 2HNO_{3} + 3H_{2}so_{4} = 3Fe_{2}(so_{4})_{3} + 2no + 4H_{2}O.

!Answer!:  0.80 cc.

81.  If 0.7530 gram of ferric nitrate (Fe(no_{3})_{3}.9H_{2}O) is dissolved in water and 1.37 cc. of HCl (sp. gr. 1.11 containing 21.92% HCl by weight) is added, how many cubic centimeters of ammonia (sp. gr. 0.96 containing 9.91% NH_{3} by weight) are required to neutralize the acid and precipitate the iron as ferric hydroxide?

!Answer!:  2.63 cc.

82.  To a suspension of 0.3100 gram of Al(Oh)_{3} in water are added 13.00 cc. of aqueous ammonia (sp. gr. 0.90 containing 28.4% NH_{3} by weight).  How many cubic centimeters of sulphuric acid (sp. gr. 1.18 containing 24.7% H_{2}so_{4} by weight) must be added to the mixture in order to bring the aluminium into solution?

!Answer!:  34.8 cc.

83.  How many cubic centimeters of sulphurous acid (sp. gr. 1.04 containing 75 grams so_{2} per liter) are required to reduce the iron in 1 gram of ferric alum (KFe(so_{4})_{2}.12H_{2}O)?  Fe_{2}(so_{4})_{3} + so_{2} + 2H_{2}O = 2FeSO_{4} + 2H_{2}so_{4}.

!Answer!:  0.85 cc.

84.  How many cubic centimeters of a solution of potassium bichromate containing 26.30 grams of K_{2}Cr_{2}O_{7} per liter must be taken in order to yield 0.6033 gram of Cr_{2}O_{3} after reduction and precipitation of the chromium?

K_{2}Cr_{2}O_{7} + 3so_{2} + H_{2}so_{4} = K_{2}so_{4} +
Cr_{2}(so_{4})_{3} + H_{2}O.

!Answer!:  44.39 cc.

85.  How many cubic centimeters of ammonium hydroxide (sp. gr. 0.946 containing 13.88% NH_{3} by weight) are required to precipitate the iron as Fe(Oh)_{3} from a sample of pure FeSO_{4}.(NH_{4})_{2}so_{4}.6H_{2}O, which requires 0.34 cc. of nitric acid (sp. gr. 1.350 containing 55.79% HNO_{3} by weight) for oxidation of the iron? (See problem No. 80 for reaction.)

!Answer!:  4.74 cc.

86.  In the analysis of an iron ore by solution, oxidation and precipitation of the iron as Fe(Oh)_{3}, what weight of sample must be taken for analysis so that each one hundredth of a gram of the ignited precipitate of Fe_{2}O_{3} shall represent one tenth of one per cent of iron?

!Answer!:  6.99 grams.

87.  What weight in grams of impure ferrous ammonium sulphate should be taken for analysis so that the number of centigrams of BaSO_{4} obtained will represent five times the percentage of sulphur in the sample?

!Answer!:  0.6870 gram.

88.  What weight of magnetite must be taken for analysis in order that, after precipitating and igniting all the iron to Fe_{2}O_{3}, the percentage of Fe_{2}O_{4} in the sample may be found by multiplying the weight in grams of the ignited precipitate by 100?