1. What metals and compounds studied are prepared by electrolysis? 2. Write the equation for the reaction between aluminium and hydrochloric acid; between aluminium and sulphuric acid (in two steps). 3. What hydroxides other than aluminium hydroxide have both acid and basic properties? 4. Write equations showing the methods used for preparing aluminium hydroxide and sulphate. 5. Write the general formula of an alum, representing an atom of an alkali metal by X and an atom of a trivalent metal by Y. 6. What is meant by the term polysilicic acid, as used in the discussion of aluminium silicates? 7. Compare the properties of the hydroxides of the different groups of metals so far studied. 8. In what respects does aluminium oxide differ from calcium oxide in properties? 9. Supposing bauxite to be 90% aluminium hydroxide, what weight of it is necessary for the preparation of 100 kg. of aluminium? CHAPTER XXVII THE IRON FAMILY =================================================================== | | | | | | | | | APPROXIMATE | | SYMBOL | ATOMIC | DENSITY | MELTING | OXIDES | | WEIGHT | | POINT | ________|________|________|_________|_____________|________________ | | | | | Iron | Fe | 55.9 | 7.93 | 1800 deg. | FeO, Fe_{2}O_{3} Cobalt | Co | 59.0 | 8.55 | 1800 deg. | CoO, Co_{2}O_{3} Nickel | Ni | 58.7 | 8.9 | 1600 deg. | NiO, Ni_{2}O_{3} =================================================================== ~The family.~ The elements iron, cobalt, and nickel form a group in the eighth column of the periodic table. The atomic weights of the three are very close together, and there is not the same gradual gradation in the properties of the three elements that is noticed in the families in which the atomic weights differ considerably in magnitude. The elements are very similar in properties, the similarity being so great in the case of nickel and cobalt that it is difficult to separate them by chemical analysis. The elements occur in nature chiefly as oxides and sulphides, though they have been found in very small quantities in the native state, usually in meteorites. Their sulphides, carbonates, and phosphates are insoluble in water, the other common salts being soluble. Their salts are usually highly colored, those of iron being yellow or light green as a rule, those of nickel darker green, while cobalt salts are usually rose colored. The metals are obtained by reducing the oxides with carbon. IRON