A-LevelChemistryGroup 29701/41 · May/June 2024 · Q112 Marks
Describe the trend in the solubility of the hydroxides of magnesium, calcium and strontium. Explain your answer. most soluble > least soluble
- (a)(i)Describe the trend in the solubility of the hydroxides of magnesium, calcium and strontium. Explain your answer. most soluble > least soluble[4]
- (a)(ii)Suggest the variation in pH of saturated solutions of the hydroxides of magnesium, calcium and strontium. Explain your answer.[1]
- (b)Barium hydroxide, Ba(OH)₂, is a strong base. A 250.0 cm³ solution of Ba(OH)₂ with a pH of 12.2 is made by dissolving Ba(OH)₂ in distilled water. Calculate the mass of Ba(OH)₂ required to make this solution. Show your working. [Mᵣ: Ba(OH)₂, 171.3] mass of Ba(OH)₂ = g[4]
- (c)(i)The solubility of iron(II) hydroxide, Fe(OH)₂, is 5.85 × 10⁻⁶ mol dm⁻³ at 298 K. Write the expression for the solubility product, Ksp, of Fe(OH)₂. Ksp =[1]
- (c)(ii)Calculate the value of Ksp of Fe(OH)₂. Include its units. Ksp = units =[2]
Mark scheme
Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.
- [1] M1 strontium > calcium > magnesium
- [1] M2 ∆Hlatt and ∆Hhyd both become less exothermic / less negative
- [1] M3 ∆Hlatt changes more
- [1] M4 ∆Hsol becomes more exothermic / more negative
- [1] pH increases as the concentration of [OH⁻] ions increases
- [1] M1 [H⁺] = 10⁻¹²·² OR 6.31 × 10⁻¹³
- [1] M2 [OH⁻] = 0.0158 mol dm⁻³ ecf
- [1] M3 [Ba(OH)₂] = 0.01585 ÷ 2 = 7.92 ecf
- [1] M4 mol of Ba(OH)₂ = 0.00792 ÷ 4 = 1.98 × 10⁻³ / mass Ba(OH)₂ = 0.339 g ecf
- [1] Ksp = [Fe²⁺][OH⁻]²
- [1] M1 Ksp = 4 × (5.85 × 10⁻⁶)³ = 8.01 × 10⁻¹⁶
- [1] M2 mol³ dm⁻⁹
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →