In a titration, a solution of potassium hydroxide was added gradually from a burette to 20 cm³ of 0.080 mol dm^-3 propanoic acid at 298 K. The pH was measured and recorded at regular intervals. 

The results are shown in the graph below.

Use the graph to deduce the volume of KOH added at the end-point of the titration.

Use the graph to deduce the pH of the solution at the half-neutralisation point.

Give the expression for the acid dissociation constant, K_a, of propanoic acid, CH₃CH₂COOH.

Use your answers to parts b) and c) to determine the value of K_a for propanoic acid at 298 K.

Give your answer to 2 significant figures.

Water dissociates slightly according to the equation:

H₂O_(I) ⇌ H⁺_(aq) + OH^-_(aq)

The ionic product of water, K_w, is given by the expression

K_w = [H⁺][OH^-]

Explain why the expression for K_w does not include the concentration of water.

The graph below shows how K_w varies with temperature.

Explain, with reference to equilibrium position, why the value of K_w increases as the temperature increases.

Use the graph above to calculate the pH of pure water at body temperature, 37°C.

Give your answer to 1 decimal place.

Calculate the pH of a 0.18  mol dm^-3 solution of KOH at 37°C. 

Give your answer to 1  decimal place.

State the meaning of the term weak Brønsted-Lowry acid.

Boric acid, H₃BO₃, is a weak Brønsted acid which dissociates into ions in three stages in aqueous solution. The equation for the first dissociation is:

H₃BO_3(aq) ⇌ H⁺_(aq) + H₂BO₃^-_(aq)

The pK_a for this dissociation is 9.24.

Calculate the pH of a 6.50 x 10^-2 mol dm^-3 solution of boric acid from the pK_a value for the first dissociation.

Give your answer to 2 decimal places.

Explain the two approximations that are made in the calculation in part b).

Boric acid can undergo futher dissociation.

What is the conjugate acid of the HBO₃^2- ion?

What is the conjugate base of the HBO₃^2- ion?

Methanoic acid, HCOOH  is added to butanoic acid, CH₃(CH₂)₂COOH. A reaction takes place to form an equilibrium mixture containing two acid-base pairs.

The K_a of methanoic acid is 1.82 x 10^-4 mol dm^-3

The K_a of butanoic acid is 1.51 x 10^-5 mol dm^-3

Complete the equilibrium equation:

HCOOH  +  CH₃(CH₂)₂COOH   ⇌   ............................................   +   .............................................

For each of the 3 equilibria shown below, write 'A' or 'B' on the dotted lines below each equation to indicate whether the substance is acting as a Brønsted–Lowry acid (A) or a Brønsted–Lowry base (B).

A 25.0 cm³ sample of 7.50 x 10^-2 mol dm^-3 hydrochloric acid was placed in a beaker.

Distilled water was added until the pH of the solution was 1.35.

Calculate the total volume, in cm³, of the solution formed.

Give your answer to 3 significant figures.

Calculate the concentration of hydroxide ions, in mol dm^-3, in the hydrochloric acid solution after the addition of distilled water.

Give your answer to 3 significant figures.

K_w = 1.00 × 10^-14 mol² dm^-6