Question

How is hydrogen obtained from

i) dilute sulphuric acid

ii) sodium hydroxide

iii) water?

Answer 1

1. Metal react with dil. sulphuric acid to form metal salt and hydrogen gas.

$$\begin{gathered} \mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\stackrel{}{\to {\mathrm{MgSO}}_4}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{Magnesium}\mathrm{sulphuric}\mathrm{acid}\mathrm{Magnesium}\mathrm{sulphate}\mathrm{Hydrogen} \end{gathered}$$

2. Hydrogen is obtained from zinc, when zinc react with sodium hydroxide.

$$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\stackrel{}{\to {\mathrm{Na}}_2}{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{Zinc}\mathrm{sodium}\mathrm{hydroxide}\mathrm{sodium}\mathrm{zincate}\mathrm{Hydrogen} \end{gathered}$$

3. Hydrogen is obtained, when acidified water is electrolyzed using platinum electrodes. Hydrogen gas evolved at cathode.

$$\begin{gathered} {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right) \\ \mathrm{At}\mathrm{cathode}:2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\stackrel{}{\to 2\mathrm{H}\stackrel{}{\to {\mathrm{H}}_2}} \\ \mathrm{At}\mathrm{anode}:{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)\stackrel{}{\to }\mathrm{OH}+{\mathrm{e}}^{-} \\ 4{\mathrm{OH}}^{-}+4{\mathrm{e}}^{-}\stackrel{}{\to }2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2 \end{gathered}$$