Quick questions on Strong vs weak acids and bases (degree of ionisation) explained: HSC Chemistry Module 6

Electrical conductivity of a solution depends on the total concentration of ions. At equal acid concentration, a strong acid produces many more ions than a weak acid, so it conducts much better.

For two solutions of equal concentration:

When a weak acid is diluted, the percent ionisation increases. Mathematically, if $K_a$ is fixed and $c$ decreases, then $x/c = \sqrt{K_a/c}$ grows. In the limit of infinite dilution every weak acid becomes 100 percent ionised. This is a Le Chatelier consequence: dilution favours the side with more particles.

Distinguish between the strength and concentration of an acid using the terms ionisation and moles per litre. [3 marks]

A 0.20 mol L$^{-1}$ solution of a weak acid HA has pH 3.40. Calculate the percent ionisation and the $K_a$ of HA. [3 marks]

Two solutions are tested with a conductivity probe: 0.10 mol L$^{-1}$ HCl reads 39 mS cm$^{-1}$ and 0.10 mol L$^{-1}$ $CH_3COOH$ reads 1.3 mS cm$^{-1}$. (a) Account for the difference. (b) Predict the conductivity of 0.010 mol L$^{-1}$ HCl.