Chemical changes Study Guide

This core practical involves reacting a metal oxide (copper oxide) with an acid (sulfuric acid) to produce a salt (copper sulfate) and water. The process requires careful technique to ensure the crystals are pure and dry. The reaction is an acid-base neutralisation, producing copper sulfate, which is soluble in water. Unreacted copper oxide is removed by filtration. The solution is then gently heated to concentrate it, promoting crystal formation upon cooling. A water bath is used during heating to provide a gentle, controlled and even heat, preventing the solution from boiling too vigorously and ensuring the production of larger, purer crystals. The crystals are then separated, washed with a small amount of cold water, and dried to remove any remaining impurities and moisture.

When preparing a soluble salt from a soluble acid and a soluble reactant (like an alkali), a titration method is essential. This is because both reactants are soluble and will not form a visible precipitate to indicate the end of the reaction. Titration allows for precise measurement of the volumes of acid and alkali required to achieve exact neutralisation. By using indicators in a preliminary titration run, the exact stoichiometric ratio of reactants can be determined. Afterwards, a second preparation can be carried out without the indicator, ensuring that the resulting solution contains only the desired salt and water, without any unreacted acid or alkali which could contaminate the final product. This purity is crucial for crystallisation and subsequent applications.