7.2. Brønsted–Lowry theory of acids and bases
A subsection of Chemistry, 9701, through 7. Equilibria
Listing 10 of 133 questions
Write an expression for the Ka of the weak acid HA in terms of the concentrations of the species involved. Ka =  The hydroxylammonium ion, HONH3 +, is a weak acid. A 1.00 × 10–3 mol dm–3 solution of hydroxylammonium ions has a pH of 4.41. Calculate the Ka of HONH3 +.  Ka = Calculate the pKa of HONH3 +.  pKa = The solubility product of manganese(hydroxide, Mn(OH)2, in water is 1.1×10–11 mol3 dm–9 at 298 K. Calculate the solubility of Mn(OH)2 in water at 298 K.  solubility = mol dm–3 
9701_w20_qp_42
THEORY
2020
Paper 4, Variant 2
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The pH of a saturated solution of calcium hydroxide is 12.35 at 298 K. Show that the concentration of hydroxide ions in a saturated solution of calcium hydroxide is 0.0224 mol dm–3 at 298 K. Use data given in to calculate the solubility product, Ksp, of calcium hydroxide at 298 K. Include the units of Ksp in your answer. Ksp = units A spatula measure of solid calcium chloride is stirred into a sample of saturated calcium hydroxide solution. All of the calcium chloride dissolves. Describe one other observation that would be made and give an estimated value of the pH of the solution obtained. Explain both your answers. observation pH of solution explanation Calcium hydroxide reacts with dilute sulfuric acid to form calcium sulfate. Barium hydroxide behaves in a similar way, forming barium sulfate. Explain why calcium sulfate is more soluble in water than barium sulfate. Some solid calcium is added to an excess of aqueous ethanoic acid, CH3COOH, and left until all the calcium has reacted. The resulting mixture, mixture D, contains no undissolved solids. Write an equation for the reaction of calcium with CH3COOH. Use formulae of molecules and ions to identify two conjugate acid–base pairs present in mixture D. Pair 1 should consist of organic species. pair 1: conjugate acid conjugate base pair 2: conjugate acid conjugate base Write the expression for the Ka of CH3COOH. Ka = The concentration of calcium ethanoate, (CH3COO)2Ca, in mixture D is 0.394 mol dm–3. The concentration of CH3COOH in mixture D is 0.270 mol dm–3. The Ka of CH3COOH is 1.74 × 10–5 mol dm–3 at 298 K. Calculate the pH of mixture D. pH = Write two equations to show how mixture D can act as a buffer solution. equation 1 equation 2
9701_w24_qp_42
THEORY
2024
Paper 4, Variant 2
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