Chemistry Open-Ended Questions

o 15.

(a) Answer ; The pH value increases as the concentration of hydrochloric acid decreases .

(b) (i) Answer; The pH value of a solution is dependent on the concentration of H+ ions. The higher the concentration of H+ ions, the lower the pH value. 0.1 mol/dm³ hydrochloric acid lonises to give 0.1 mol/dm³ H+ ions. 0.1 mol/dm³ sulfuric acid ionises to give O.2 mol/dm³ H ions. Hence, the pH value observed for 0.1 mol/dm³ sulfuric was smaller than that for 0.1 mol/dm³ hydrochloric acid.

( ii ) Answer; Both 0.1 mol/dm³ sulfuric acid and 0.1 mol/dm³ hydrochloric acid will give a red colour with Universal Indicator. *(I'm not sure about this complete answer )

( iii ) Answer; The pH value likely to be between 5 to 7, Hydrochloric acid is a strong acid which fully ionises in water. Ethanoic acid is a weak acid which does not fully ionise in water. Hence, the concentration of H+ ions in 0.00001 mol/dm³ ethanoic acid will be lower than that in 0.00001 mol/dm³ hydrochloric acid. Therefore, the pH value of ethanoic acid will be greater than 5.