How Can You Produce CuCl2 from CuSO4?

You can convert copper(II) sulfate, CuSO4, into copper(II) chloride, CuCl2, by adding a soluble chloride salt that removes sulfate from solution. A common laboratory choice is barium chloride, BaCl2. The key is that the reaction produces insoluble barium sulfate, so filtering separates it from the copper-containing solution.

The reaction

The balanced molecular equation is:

$$\mathrm{CuSO_4(aq) + BaCl_2(aq) \rightarrow CuCl_2(aq) + BaSO_4(s)}$$

In water, the important net ionic change is:

$$\mathrm{Ba^{2+}(aq) + SO_4^{2-}(aq) \rightarrow BaSO_4(s)}$$

Barium sulfate is sparingly soluble and appears as a white solid. Copper(II) ions and chloride ions remain in the water, so the filtered liquid contains CuCl2. The reaction has a 1:1 mole ratio: one mole of BaCl2 reacts with one mole of CuSO4.

Preparation in a laboratory

1. Dissolve a measured amount of copper(II) sulfate in water.
2. Separately dissolve the stoichiometric amount of barium chloride in water. Account for whether your reagent is anhydrous or hydrated; the required mass depends on its formula.
3. Stir the barium chloride solution into the copper sulfate solution. A white BaSO4 precipitate forms.
4. Let the solid settle, then filter the mixture. The filtrate is an aqueous copper(II) chloride solution; the filter cake is primarily BaSO4.
5. To obtain crystals, gently concentrate the filtrate and let it cool. Copper(II) chloride commonly crystallizes as the dihydrate, CuCl2·2H2O, rather than as water-free CuCl2.

Do not evaporate the solution to dryness unless a procedure specifically requires it. Concentration and cooling are generally used to crystallize the hydrated salt; the exact result depends on temperature and how much water remains.

Worked amount calculation

Suppose you start with 0.100 mol of CuSO4. The equation requires 0.100 mol of BaCl2.

For anhydrous barium chloride, with molar mass about 208.23 g/mol:

$$0.100\ \mathrm{mol} \times 208.23\ \mathrm{g/mol} = 20.82\ \mathrm{g}$$

So use 20.82 g of anhydrous BaCl2. If your reagent is BaCl2·2H2O, its molar mass is about 244.26 g/mol, so the corresponding amount is:

$$0.100\ \mathrm{mol} \times 244.26\ \mathrm{g/mol} = 24.43\ \mathrm{g}$$

Theoretical yields for this amount are 0.100 mol of BaSO4, or about 23.34 g, and 0.100 mol of CuCl2. If the copper salt crystallizes as CuCl2·2H2O, that corresponds to about 17.05 g of dihydrate. These are theoretical quantities: transfer losses, incomplete crystallization, and dissolved product in the remaining liquid can reduce the amount collected.

If your copper sulfate is itself hydrated, such as CuSO4·5H2O, count moles using the full hydrate’s molar mass. One mole of CuSO4·5H2O still supplies one mole of CuSO4 units for the reaction.

Why adding table salt is not enough

Sodium chloride also supplies chloride ions, but mixing NaCl with CuSO4 in water does not provide a convenient separation. Sodium sulfate and copper(II) chloride remain dissolved, so there is no precipitate to filter away and no straightforward way to isolate CuCl2 by this reaction alone. The barium method works because BaSO4 is poorly soluble.

Other sulfate-removing reagents may be possible, but they must form a separable sulfate compound and must not introduce ions that contaminate the desired product. Barium chloride is a common textbook example, not a household-safe reagent.

Common mistakes and safety

• Using equal masses instead of equal moles: The 1:1 ratio is a mole ratio. Convert reagent masses to moles, using the correct hydrate formula.
• Assuming the crystals are anhydrous: Crystallization from water commonly gives CuCl2·2H2O. Report the hydrate if that is what you obtained.
• Expecting evaporation to remove every impurity: Filtration removes solid BaSO4, but dissolved impurities remain in the filtrate and may enter the crystals.
• Treating the materials as harmless: Barium chloride is toxic, and copper compounds can be harmful and environmentally hazardous. Work only with suitable laboratory supervision, protective equipment, and waste procedures. Collect the barium-containing solid and copper-containing liquids as appropriate hazardous chemical waste; do not pour them down a drain.