Question

(a) What are strong acids and weak bases? Give an example for each. [2 Marks]
(b) Define neutralisation reaction. Give an eample.
[2 Marks]
(c) Complete the following reactions and identify the salts obtained as acidic, basic, or neutral. Comment on the pH of the solution obtained after the reaction. Give reasons to justify your answer.
(i) $HCl\left(aq\right)+N{H}_{4}OH\left(aq\right)$ →
(ii) $C{H}_{3}COOH\left(aq\right)+KOH\left(aq\right)$ →
[4 Marks]

Answer 1

(a) Strong acids: These are the substances which dissociate almost completely in aqueous solutions to produce $H^{+}$ ions and the respective acidic radicals.
Example: Hydrochloric acid $\left(HCl\right)$
[1 Mark]
Weak bases: These are the substances which dissociate partially in aqueous solution to produce small amounts of $O{H}^{-}$ ions and respective basic radicals.
Example: Ammonium hydroxide $\left(N{H}_{4}OH\right)$
[1 Mark]
(b) A neutralisation reaction is a reaction in which an acid and a base react with each other to form salt and water.
Acid + Base → Salt + Water
[1 Mark]
Example:
$HCl\left(aq\right)+NaOH\left(aq\right)$ → $NaCl\left(aq\right)+H_{2}O\left(l\right)$
[1 Mark]
(c) The complete reactions are as followed:
(i) $HCl\left(aq\right)+N{H}_{4}OH\left(aq\right)\to N{H}_{4}Cl\left(aq\right)+H_{2}O\left(l\right)$
[1 Mark]
Strong acids react with weak bases to produce acidic salt and water.
As water is neutral but $\left(N{H}_{4}Cl\right)$ is acidic, the solution will have pH < 7.
[1 Mark]

(ii) $C{H}_{3}COOH\left(aq\right)+KOH\left(aq\right)\to C{H}_{3}COOK\left(aq\right)+H_{2}O\left(l\right)$
[1 Mark]
Weak acids react with strong bases to produce basic salt and water. As water is neutral but $C{H}_{3}COOK$ is basic, the solution will have pH > 7.
[1 Mark]