(a) Give one reason why a collision between reactants may not produce new species. (b) Explain, illustrating with appropriate equation(s), why an aqueous so...
Question 1 Report
(a) Give one reason why a collision between reactants may not produce new species.
(b) Explain, illustrating with appropriate equation(s), why an aqueous solution of aluminium chloride is acidic.
Answer Details
(a) Why a collision between reactants may not produce new species
For a collision to be effective (fruitful) the colliding particles must have energy equal to or greater than the activation energy and must collide with the correct orientation. A collision fails to form products if the particles collide with too little energy (below the activation energy) or with an unfavourable orientation, so they simply bounce apart unchanged.
(b) Why aqueous aluminium chloride is acidic
The aluminium ion, \(Al^{3+}\), is very small and highly charged, so it strongly attracts and polarises the water molecules bonded to it. This causes hydrolysis (cationic hydrolysis): a bonded water molecule releases a hydrogen ion, so the solution contains an excess of \(H^+\) ions and is acidic.
Using the hydrated ion:
\[[Al(H_2O)_6]^{3+} \rightleftharpoons [Al(H_2O)_5(OH)]^{2+} + H^+\]or, written simply:
\[AlCl_3 + 3H_2O \rightleftharpoons Al(OH)_3 + 3HCl\]The liberated \(H^+\) (hydrochloric acid) makes the solution acidic.
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