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Hydrogen — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryHydrogen5 Marks
Question
  1. How would you prepare dihydrogen from water by using a reducing agent?
  2. How would you prepare dihydrogen from a substance other than water?
  3. How would you prepare very pure dihydrogen in the laboratory?
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Answer

  1. Sodium metal is a good reducing agent. It reduces water to hydrogen (or dihydrogen).
$2\text{H}_2\text{O}+2\text{Na}\xrightarrow{\ \ \ \ \ \\ \ \ }2\text{NaOH}+\text{H}_2(\text{g)}$
  1. Dihydrogen can be obtained by treating zinc with dilute.
$\text{HCl}\text{ Zn}(\text{s})+2\text{HCl}(\text{aq})\rightarrow\text{ZnCl}_2(\text{aq})+\text{H}_2(\text{g})$
  1. Highly pure dihydrogen (hydrogen gas) can be prepared by the following methods.
  1. Fairly pure hydrogen can be obtained by treating pure magnesium or pure aluminium with chemically pure $H_2SO_4$ or HCl diluted with distilled water. The gas is passed over $P_2O_5$ and is collected by the displacement of mercury.
$\text{Mg}(\text{g})+\text{H}_2\text{SO}_4(\text{aq})\xrightarrow{\ \ \ \ \ \ \ \ \ }\text{MgSO}_4(\text{aq})+\text{H}_4(\text{g})$
  1. Highly pure hydrogen gas can be obtained by electrolysing a warm solution of $Ba(OH)_2​​​​​​​$​​​​​​​ in a U-tube using nickel electrodes. The gas is purified by passing it over heated platinum gauze when traces of oxygen combine with hydrogen forming water.
The gas is then dried by passing it over caustic potash sticks and phophorus pentoxide. Hydrogen is finally adsorbed in palladium and the impurities remain unadsorbed. On heating palladium under reduced pressure, pure hydrogen is liberated.

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