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?