Calcium oxide can be prepared by heating calcium in oxygen. In nature, carbon dioxide in the atmosphere reacts with calcium hydroxide to produce calcium carbonate. Hard water, containing calcium bicarbonate as hardness, may be softened by adding sodium hydroxide. Sodium carbonate, calcium carbonate, and water all are formed in the reaction. Permanent hard water contains calcium sulfate and can be softened by the addition of sodium carbonate.
Beryllium hydroxide is amphoteric.
Gadolinium, europium, and samarium may all be prepared in the same way as terbium. All of these elements have a valence of 3. 23. The metals manganese, chromium, indium, and tin are all prepared by the reduction of their oxides with carbon. Lanthanum and cerium may be obtained in the free state by fusing their respective chlorides with metallic potassium. 75 g of potassium hydroxide are permitted to react with 50.0 g of hydrochloric acid.