pH calculations

This question is about acids and bases.

Nitric acid is a strong acid.

Calculate the pH of 0.150 mol dm^–3 nitric acid.

Give your answer to 2 decimal places.

Propanoic acid is a weak acid.

Calculate the concentration of a solution of propanoic acid with pH = 2.89 at 25 °C

The acid dissociation constant (K_a) for propanoic acid at 25 °C

A student records the pH as an alkali is added to an acid.

Figure 3 shows the pH curve for this reaction.

Which of these combinations gives the pH curve shown in Figure 3 ?

Different indicators change colour across different pH ranges.

Buffer solution B is made by dissolving 0.656 g of sodium ethanoate (M_r = 82.0) in 50 cm³ of 0.120 mol dm^–3 ethanoic acid.

This buffer solution has pH = 4.87

Explain, qualitatively, how this buffer solution resists pH change when a small amount of sodium hydroxide solution is added.

Calculate the pH change that occurs when 1.50 cm³ of 0.200 mol dm^–3 HCl(aq) are added to buffer solution B.

Give your answer to 2 decimal places.

The acid dissociation constant (K_a) for ethanoic acid at 25 °C is 1.78 × 10^–5 mol dm^–3

At 40 °C the ionic product of water, K_w = 2.92 × 10^–14 mol² dm^–6

Give the expression for K_w

Calculate the pH of pure water at 40 °C Give your answer to 2 decimal places.

35.0 cm³ of 0.150 mol dm^–3 aqueous sodium hydroxide are mixed with 20.0 cm³ of a 0.100 mol dm^–3 solution of hydrochloric acid. The temperature of the solution formed is 40 °C

Calculate the pH of the solution formed. Give your answer to 2 decimal places.

A strong acid H₂X dissociates in aqueous solution.

What is the pH of a 0.020 mol dm^–3 solution of this acid?

This question is about pH.

Pure water dissociates slightly.

The ionic product of water, K_w = [H⁺][OH⁻]

Explain why [H₂O] is not shown in the K_w expression.

Table 5 shows how K_w varies with temperature.

Explain why the value of K_w increases as the temperature increases.

Give the expression for pH.

Calculate the pH of pure water at 50 °C Give your answer to 2 decimal places.

Explain why water is neutral at 50 °C

Calculation

A pH meter is calibrated using a calibration graph. To create the calibration, the pH meter is used to measure the pH of separate solutions, each with a known, accurate pH.

Figure 3 shows the calibration graph.

Use Figure 3 to give the true pH value when the pH meter reading is 5.6

Suggest why the pH probe is washed with distilled water between each of the calibration measurements.

The calibrated pH meter is used to monitor the pH during a titration of hydrochloric acid with sodium hydroxide.

Explain why the volume of sodium hydroxide solution added between each pH measurement is smaller as the end point of the titration is approached.

Table 6 shows data about some indicators.

The student plans to do the titration again using one of the indicators in Table 6 to determine the end point.

State why all three of the indicators in Table 6 are suitable for this titration.

36.25 cm³ of 0.200 mol dm^–3 sodium hydroxide solution are added to 25.00 cm³ of 0.150 mol dm^–3 hydrochloric acid.

Calculate the pH of the final solution at 25 ºC

A mixture of methanoic acid and sodium methanoate in aqueous solution acts as an acidic buffer solution.

The equation shows the dissociation of methanoic acid.

Calculate the mass, in g, of sodium methanoate (HCOONa) that must be added to 25.0 cm³ of 0.100 mol dm³ methanoic acid to produce a buffer solution with pH = 4.05 at 298 K

For methanoic acid, pK_a = 3.75 at 298 K

Assume that the volume of the solution remains constant.

Which statement about pH is correct?

Which is the concentration of NaOH(aq), in mol dm^–3, that has pH = 14.30?

What is the pH of 0.015 mol dm^–3 sulfuric acid?

This question is about different pH values.

For pure water at 40 °C, pH = 6.67 A student thought that the water was acidic.

Explain why the student was incorrect.

Determine the value of K_w at this temperature.

Sodium hydroxide solution was added gradually from a burette to 25 cm³ of 0.080 mol dm^–3 propanoic acid at 25 °C The pH was measured and recorded at regular intervals.

The results are shown in Figure 4.

Use Figure 4 to determine the value of K_a for propanoic acid at 25 °C

Show your working.

Suggest which indicator is the most appropriate for the reaction in Question 09.2 ? Tick (✓) one box.

Indicator	pH range	Tick () one box
methyl orange	3.1 – 4.4
bromothymol blue	6.0 – 7.6
cresolphthalein	8.2 – 9.8
indigo carmine	11.6 – 13.0

A student prepared a buffer solution by adding 0.0136 mol of a salt KX to 100 cm³ of a 0.500 mol dm^–3 solution of a weak acid HX and mixing thoroughly.

The student then added 3.00 × 10^–4 mol of potassium hydroxide to the buffer solution.

Calculate the pH of the buffer solution after adding the potassium hydroxide.

For the weak acid HX at 25 °C the value of the acid dissociation constant,

Give your answer to two decimal places.

A buffer solution has a constant pH even when diluted.

Use a mathematical expression to explain this.