Ncert Exercises & Solutions

56. Why can dilute solutions of hydrogen peroxide not be concentrated by heating? How can a concentrated solution of hydrogen peroxide be obtained?

Dilute solutions of H₂O₂ cannot be concentrated by heating because it decomposes much blow its boiling point.

2 H_{2} O_{2} \to 2 H_{2} O + O_{2}

1% H₂O₂ is extracted with water and concentrated to

~

30% (by mass) by distillation under reduced pressure. It can be further concentrated to

~

85% by careful distillation under low pressure. The remaining water can be frozen out to obtain pure H₂O₂.