Simulic
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Making a salt – copper sulfate crystals from an insoluble base and acid

Integrated ScienceChemical ReactionsAges 13–14

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Carry out the soluble-salt preparation step by step: warm dilute acid (H₂SO₄ or HCl), add an insoluble base (CuO, CuCO₃ with fizzing, or ZnO) one spatula at a time until it is in excess, filter off the excess, heat the filtrate to the point of crystallisation (tested with a cold glass rod), cool slowly or quickly, then dry and weigh the crystals. A solubility graph shows why crystals form on cooling, and a step-by-step calculation gives the theoretical yield from the moles of acid, the percentage yield and where the losses went – including the mistake of evaporating to dryness.

Lesson: Preparing a soluble salt from an acid and an insoluble base

What it shows

A soluble salt can be made by reacting a dilute acid with an insoluble base such as copper(II) oxide. Adding the base until some is left over makes sure all the acid has reacted; the excess is filtered off. Heating the filtrate to the point of crystallisation and then cooling it lets hydrated crystals such as CuSO₄·5H₂O form, because the salt is less soluble when cold. The theoretical yield comes from the moles of acid, the limiting reagent. Some salt always stays dissolved in the leftover solution, so the percentage yield is below 100%.

How to use

Choose the Acid, Base, Volume and Concentration, then press 1. Warm the acid. Add the base with + 1 spatula until solid stays at the bottom, then follow the numbered buttons: filter, evaporate, cool and dry. Auto run does all steps. Compare Cooling options and the Evaporate setting in the results table and the yield calculation.

Parameters you can change

  • Dilute acid Sulfuric acid H₂SO₄, Hydrochloric acid HCl
  • Insoluble base Copper(II) oxide CuO, Copper(II) carbonate CuCO₃, Zinc oxide ZnO
  • Volume of acid 10–50 cm³
  • Acid concentration 0.5–2 mol/dm³
  • Cooling Cool slowly at room temperature, Cool quickly in an ice bath
  • Evaporate the solution To the point of crystallisation (correct), To dryness (mistake)

Questions to explore

  1. Why is the base added until some is left over before the mixture is filtered?
  2. Why does evaporating to dryness give a lower mass than the theoretical mass of CuSO₄·5H₂O?
  3. How do slow cooling and cooling in an ice bath change the size of the crystals?

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