Preparation of Crystals of Soluble Salts

Soluble salts can be prepared by reacting an acid with a base or an alkali, in a displacement reaction. This base might be a metal oxide, a metal hydroxide or a metal carbonate.
The initial step involves mixing the chosen acid with a high quantity of the chosen base/alkali. The mixture is heated/stirred continuously until the base/alkali is fully reacted.
The solution obtained contains a salt and water, if a base was used. If a carbonate was used, the solution contains salt, water, and carbon dioxide.
If any unreacted base/alkali or unreacted acid might be present in the solution, those could be removed by filtration.
The next phase is to obtain the salt from the solution. To accomplish this, gently heat the solution until most of the water has evaporated, leaving a highly concentrated solution of the salt.
Very important is to avoid overheating the concentrated solution as some salts can decompose under heat.
Once the solution has become saturated, any further salt will start to crystallise out as it can no longer be held in solution.
At this point, the solution should be left to cool. As it cools, more and more of the salt will crystallise out of the solution.
The crystals can be separated from the remaining solution by filtration.
After this, the wet crystalline solid that collects on the philtre paper should be gently dried, for example with a drying oven or in desiccators to prevent decomposition.
This method could generate hydrated crystals if the salt is hydrated.
For example, to prepare copper sulphate crystals, react sulfuric acid (H2SO4) with an excess of black copper oxide (CuO), to form blue copper sulphate crystals. Filter, then evaporate the water, leaving behind blue copper sulphate crystals.
The key to success in this process is a good control of heat and a careful observation. A good indicator that all of the water has evaporated is that crystals will start to form on the surface of the solution.