Question 7

7.1 Two acids, HX and HY, of EQUAL CONCENTRATIONS are compared.
The pH of HX is 2,7 and the pH of HY is 0,7.

7.1.1 Define an acid in terms of the Lowry-Brønsted theory. (2)

7.1.2 Which acid, HX or HY, is STRONGER? Give a reason for the answer. (2)

7.1.3 Acid HX ionises in water according to the following equation:

The K_a value for the reaction is 1,8 x 10^-5 at 25 °C.
Is the concentration of the hydronium ions HIGHER THAN, LOWER THAN or EQUAL TO the concentration of HX? Give a reason for the answer. (2)

7.2 Learners add 150 cm³ of a sodium hydroxide solution, NaOH, of unknown
concentration to 200 cm³ of a 0,03 mol∙dm^-3 hydrochloric acid solution, HCℓ, as illustrated below. They find that the pH of the final solution is 2.
Assume that the volumes are additive.

The balanced equation for the reaction is:
HCℓ(aq) + NaOH(aq) → NaCℓ(aq) + H₂O(ℓ)

Calculate the:
7.2.1 Concentration of the H₃O⁺ ions in the final solution (3)

7.2.2 Initial concentration of the NaOH(aq) (7)
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