Acids, Bases and Salt Preparations: Answers
Write equations for the reactions between: potassium and sulfuric acid, magnesium oxide and hydrochloric acid, copper carbonate and nitric acid.
Potassium + sulfuric acid —> potassium sulfate and hydrogen (remember acid + metal —> salt + hydrogen).
Magnesium oxide + hydrochloric acid —> magnesium chloride + water (remember acid + metal oxide —> salt + water).
Copper carbonate + nitric acid —> copper nitrate + water + carbon dioxide (remember acid + metal carbonate —> salt + water + carbon dioxide)
State whether the following salts are soluble or insoluble: potassium carbonate, barium hydroxide, barium sulfate, silver bromide, ammonium nitrate.
Potassium carbonate is soluble - any salts containing potassium (along with sodium and ammonium) are always soluble.
Barium hydroxide is insoluble - all hydroxides are insoluble except those containing potassium, sodium or ammonium.
Barium sulfate is insoluble - all sulfates are insoluble except those containing barium, lead and calcium.
Silver bromide is insoluble - all silver halides are insoluble and are used as the test for halide (group 7) ions.
Ammonium nitrate is soluble - all nitrates are soluble.
Describe a method you would use to produce the insoluble salt calcium carbonate.
To form an insoluble salt, we need to mix together two soluble salts. To form calcium carbonate, we need a soluble salt containing calcium, such as calcium nitrate. We also need a soluble salt containing carbonate, such as potassium carbonate (refer to the solubility rules to check which other salts would be suitable). Dissolve each salt in a test tube containing water then add to a beaker and stir to mix. A precipitate of calcium carbonate will form which can be removed by filtration. The salt can be washed and dried.
Describe a method you would use to produce the soluble salt magnesium chloride from magnesium oxide (an insoluble base).
Heat hydrochloric acid in a water bath then add the magnesium oxide. The magnesium oxide should be in excess. When no more magnesium oxide reacts, the left-over magnesium oxide can be removed by filtration. The remaining solution is allowed to evaporate to remove the water. The salt should then be left to slowly crystallise. The crystals can be washed and dried.