This diagram is from a school investigation of ammonium chloride. A student placed a small mass of solid ammonium chloride at one end of a dry hard-glass tu...
Question 1 Report
This diagram is from a school investigation of ammonium chloride. A student placed a small mass of solid ammonium chloride at one end of a dry hard-glass tube and heated it gently. After several minutes, a white solid appeared on the cooler part of the tube. The student was told that gaseous ammonia and hydrogen chloride can form near the heated solid and can react again as they move to a cooler region. The tube is not sealed, so the observation is used to discuss a reversible reaction rather than a full equilibrium mixture.
(a) Name the white solid initially heated in the tube. [1]
(b) Complete the equation for the change near the heated end.
NH4Cl(s) ⇆ ................. + ................. [2]
(c) State the two gases that diffuse towards the cooler part of the tube. [2]
(d) Explain why a white solid forms in the cool region. [3]
(e) Give one change needed to allow a true equilibrium to become established in this experiment. [2]
Answer Details
(a) The solid initially heated is ammonium chloride. [1]
(b) Near the heated end:
\[\mathrm{NH_4Cl(s)\rightleftharpoons NH_3(g)+HCl(g)}\]
Ammonia, \(\mathrm{NH_3(g)}\), gains one mark and hydrogen chloride, \(\mathrm{HCl(g)}\), gains one mark. [2]
(c) The gases diffusing to the cooler region are ammonia [1] and hydrogen chloride. [1] [2]
(d) The ammonia and hydrogen chloride gases meet in the cooler region. [1] They react together [1] to form solid ammonium chloride, which deposits as a white solid. [1] [3]
(e) The tube must be sealed, or a closed container used. [1] Then no gas can escape and both the forward and reverse reactions can continue, allowing a true equilibrium to form. [1] [2]
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