Question

12. Fill in the blank from the choices given within bracket.

Ammonia gas is collected by _________ (an upward displacement of air/a downward displacement of water/a downward displacement of air).

Answer 1

• Haber's technique generates ammonia gas.
• The following is the reaction:
  $$\begin{gathered} {\mathrm{N}}_{2\left(\mathrm{g}\right)}+3{\mathrm{H}}_{2\left(\mathrm{g}\right)}\rightleftharpoons 2{\mathrm{NH}}_{3\left(\mathrm{g}\right)} \\ ∆\mathrm{H}=-92kJ\mathit{/}mol \end{gathered}$$
• The temperature must be low and the pressure must be high in order to produce more ammonia. The catalyst has no impact on the generation of ammonia.
• Ammonium gas is made in the laboratory by slowly heating ammonium chloride $\left({\mathrm{NH}}_3\mathrm{Cl}\right)$ with slaked time $\left[\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right]$.
  $2{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)\to {\mathrm{CaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+2{\mathrm{NH}}_3\left(\mathrm{aq}\right)$
• Because ammonia gas is lighter than air, it is collected by downward displacement of air. Because ammonia is soluble in water, it cannot be gathered on top of it.
• So, ammonia gas is collected by a downward displacement of air.