Chevreuls Salt

Preparation of a red salt precipitate which has interesting properties

Scientific name: Partial reduction of copper to form a salt of copper in a mixed oxidation state

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Safety

Wear eye protection goggles.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

6 CuSO4 + 3 Na2S2O5 + 7 H2O → 2 Cu3(SO3)2*2H2O + 3 H2SO4 + 3 Na2SO4

Cu3(SO3)2*2H2O + 4 HCl → 2 CuCl + CuCl2 + 2 SO2 + 4 H2O

Cu3(SO3)22H2O + 10 NH3H2O → 2 (NH4)2SO3 + (Cu(NH3)4)(OH)2 + 2 (Cu(NH3)2)OH + 8 H2O

Step-by-step instruction

  1. Grind 2.4 grams of copper sulfate in a mortar.
  2. Put it into a beaker containing 25 ml distilled water and mix, until the powder completely dissolves.
  3. Dissolve 2 g of sodium metabisulfite in another beaker containing 10 ml of water.
  4. Mix the two solutions in a large test tube. The solution should become emerald green.
  5. Heat the test tube to boiling for a few minutes, using a spirit lamp or a gas burner. The dark precipitate should form slowly, and the solution should become discolored.
  6. Pass the resulting mixture through filter paper. Red-brown precipitate should remain on the filter.
  7. Examine the properties of the resulting salt. Add dilute hydrochloric acid and aqueous ammonia to small portions of Chevreul's salt .
  8. Observe the discoloration of the precipitate and formation of the blue solution, respectively.

Scientific background

Sodium metabisulfite has reducing properties. Therefore, part of the Cu(II) may be reduced to Cu(I). The reaction proceeds as ion exchange in this solution, which explains the formation of a red precipitate of mixed salt, which contains copper in two oxidation states.

After addition of hydrochloric acid, Cu(II) passes into the solution in the form of CuCl2, and Cu(I) remains as a precipitate of CuCl which has a white color.

Cu(II) forms stable complexes with ammonia, soluble in water and colored in blue.

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Published on 16 June 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst