Question

What happens to blue vitriol when it is reacted with conc. sulphuric acid?

What happens to blue vitriol when it is reacted with conc. sulphuric acid?

NewBlackStudio Ai Solution

100% (3 rated)

Answer

Answer: Blue vitriol (copper(II) sulfate pentahydrate, CuSO4·5H2O) is dehydrated by concentrated sulfuric acid and turns into white anhydrous copper(II) sulfate (CuSO4); the acid absorbs the water of crystallization.

Explanation

  • Concentrated H2SO4 is a strong dehydrating agent. It removes the water of crystallization from blue vitriol, converting the blue hydrated salt to the white anhydrous salt.
  • Observationally you see a colour change from blue to white; if the product is exposed to moisture it will rehydrate and turn blue again.

Chemical equation (summary):

$$\text{CuSO}_4\cdot5\text{H}_2\text{O}\xrightarrow{\text{conc. }H_2SO_4}\text{CuSO}_4+5\text{H}_2\text{O}$$

(The liberated water is taken up by the conc. H2SO4, yielding a more hydrated/dilute sulfuric acid.)

Notes and cautions

  • The change is a physical dehydration (loss of water of crystallization), not reduction/oxidation of copper.
  • Anhydrous CuSO4 is a white, hygroscopic powder that becomes blue again on adding water.
  • Concentrated sulfuric acid is highly corrosive and the process can be exothermic — handle with proper PPE and in a fume hood.