Module 6.2 Using Brønsted–Lowry Theory

What is the concentration of hydroxide ions (in mol L^–1) in a solution that has a pH of 8.53?

• 3.0 × 10^–9

• 3.4 × 10^–6

• 5.5

• 3.0 × 10⁵

The equation for the autoionisation of water is shown.

2H₂O(l ) ↔ H₃O⁺(aq) + OH⁻(aq)

At 50°C the water ionisation constant, Kw , is 5.5 × 10⁻¹⁴.

What is the pH of water at 50°C?

• 5.50

• 6.63

• 6.93

• 7.00

An aqueous solution of sodium hydrogen carbonate has a pH greater than 7.

Which statement best explains this observation?

• H₂O(l) is a stronger acid than HCO₃⁻(aq).

• HCO₃⁻(aq) is a weaker acid than H₂CO₃(aq).

• Na⁺(aq) reacts with water to produce the strong base NaOH(aq).

• The conjugate acid of HCO₃⁻(aq) is a stronger acid than H₂O(l).

What is the pH of the resultant solution after 20.0 mL of 0.20 mol L⁻¹ HCl(aq) is mixed with 20.0 mL of 0.50 mol L⁻¹ NaOH(aq)?

• 11.8

• 13.2

• 13.5

• 14.0

Which equation shows the hydrogen carbonate ion acting as a Brønsted−Lowry acid?

• HCO₃⁻(aq) ↔ CO₃²⁻(aq) + H⁺(aq)

• HCO₃⁻(aq) + H₂O(l) ↔ H₂CO₃(aq) + OH^-(aq)

• HCO₃⁻(aq) + NH₃(aq) ↔ CO₃²⁻(aq) + NH₄⁺(aq)

• HCO₃⁻(aq) + HCOOH(aq) ↔ HCOO^-(aq) + H₂CO₃(aq)

The pH of a solution changes from 8 to 5.

What happens to the concentration of hydrogen ions during this change of pH?

• It increases by a factor of 3.

• It decreases by a factor of 3.

• It increases by a factor of 1000.

• It decreases by a factor of 1000.

Which beaker contains a concentrated strong acid?

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• 
• 
• 

Which of the following is the conjugate base of the dihydrogen phosphate ion (H₂PO₄^–)?

• H₃PO₄

• HPO₄^2-

• PO₄^3-

• OH^-

What is the hydroxide ion concentration of a solution of potassium hydroxide with a pH of 11?

• 10^–11 mol L^–1

• 10^–3 mol L^–1

• 10³ mol L^–1

• 10¹¹ mol L^–1