Short Answer TypeWhen a piece of calcium metal is dropped into a beaker of cold water, a vigorous reaction takes place and the metal gradually disappears to form a white suspension.
(i) Write down the equation for the reaction.
(ii) Why does the solution become milky?
(iii) On filtering, a clear solution is obtained. What is the name of the clear solution?
What is the importance of heavy water with regard to nuclear power generation?
Or
Discuss the importance of heavy water in nuclear reactor.
Knowing the properties of H2O and D2O, do you think that D2O can be used for drinking purposes?
Long Answer TypeWhy is concenration of hydrogen peroxide difficult?
The hydrogen peroxide prepared whether in the laboratory or on a commercial scale is quite dilute. Hence, it has to be concentrated. The concentrated of hydrogen peroxide is done very carefully because it decomposes readily on heating to water and oxygen.
The explosive decomposition of hydrogen peroxide is catalysed by the presence of organic matter and metallic ions. The concentration of the aqueous dilute solution having H2O2 is done carefully by the following methods:
(i) By cooling: The solution is frozen at 273 K. Some of the water in it separates as ice. The remaining liquid is now richer in hydrogen peroxide.
(ii) By evaporation: Hydrogen peroxide obtained above is evaporated on a water bath at about 345K. Water evaporates slowly and hydrogen peroxide of about 50% strength is obtained.
(iii) Vacuum desiccator evaporation: 50% hydrogen peroxide is placed in vacuum desiccator which contains concentrated H2SO4 (dehydrating agent). Concentrated sulphuric acid absorbs most of the water from hydrogen peroxide solution and nearly 90% hydrogen peroxide is obtained.
(iv) Vacuum distillation: 90% hydrogen peroxide obtained above is subjected to distillation under reduced pressure when water distills over at about 308-313 K at a pressure of about 15 mm and the hydrogen peroxide left is about 99% pure.
(v) Freezing with solid carbon dioxide : By freezing liquid H2O2 (99%) in a freezing mixture of solid carbon dioxide (dry ice) and ether, crystals of H2O2 separate out. These are dried and melted to get 100% pure hydrogen peroxide.
Short Answer TypeWhat precautions are necessary while storing hydrogen peroxide?
Or
Explain why hydrogen peroxide is stored in coloured/plastic bottles.
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