Question 21.4: Write balanced net ionic equations to explain why (a) alumin...
Write balanced net ionic equations to explain why
(a) aluminum hydroxide dissolves in hydrochloric acid.
(b) carbon dioxide gas is evolved when calcium carbonate is treated with hydrochloric acid.
(c) carbon dioxide gas is evolved when calcium carbonate is treated with hydrofluoric acid.
(a) When a precipitate is said to dissolve, it means that the solid is broken up into its component ions.
Al(OH)_{3}(s) → Al^{3+}(aq) + 3OH^{-}(aq)
The OH^{-} ion then reacts with the appropriate ion contributed by HCl, in this case H^{+}
OH^{-}(aq) + H^{+}(aq) → H_{2}O
The reaction is
Al(OH)_{3}(s) + 3H^{+}(aq) → Al^{3+}(aq) + 3H_{2}O
(b) Recall that a carbonate (CO_{3}^{2-}) reacts with an acid by releasing CO_{2} and water. In this case, the reacting species is H^{+} because HCl is a strong acid (Chapter 4).
CaCO_{3}(s) + 2H^{+}(aq) → Ca^{2+}(aq) + CO_{2}(g) + H_{2}O(c) As in (b), CO_{2} is evolved, but the reacting species is HF because it is a weak acid.
CaCO_{3}(s) + 2HF(aq) → Ca^{2+}(aq) + CO_{2}(g) + 2F^{-}(aq) + H_{2}O