Why can dilute solutions of hydrogen peroxide not be concentrated by heating. How can a concentrated solution of hydrogen peroxide be obtained?
The dilute solutions of hydrogen peroxide cannot be concentrated by simple heating. This is because hydrogen peroxide readily decomposes below its boiling point.So, to obtain a concentrated solution of hydrogen peroxide, the following steps are needed to done – •The diluted solution is carefully heated on a water bath. Doing slow evaporation, helps the release of water molecules and we obtain 50% solution of H2O2.•The 50% solution is placed in vacuum desiccator over concentrated sulphuric acid. The dehydrating nature of sulphuric acid absorbs water vapours and we get 90% solution of H2O2. •The 90% solution of H2O2 is then subjected to distillation under reduced pressure. Water distils over at 303 – 313 K and we get 99% pure H2O2 solution.
•The 99% solution of H2O2 is cooled in a freezing mixture of solid carbon dioxide and ether. As a result, crystals of hydrogen peroxide separate out which are removed. This gives completely pure hydrogen peroxide.
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