Enthalpy of solution, hydration and solubilityEdexcel International A Level Chemistry: Flashcards
What these 14 flashcards ask
- Define the enthalpy change of solution.
- Define the enthalpy change of hydration of an ion.
- Write the equation for the hydration of Mg²⁺.
- Is the enthalpy change of hydration exothermic or endothermic?
- Give the expression for ΔsolH using lattice energy and hydration enthalpies.
- What does 'infinitely dilute' mean?
- How does ionic charge affect hydration enthalpy and lattice energy?
- How does ionic radius affect hydration enthalpy and lattice energy?
- Why is the hydration enthalpy of Mg²⁺ more exothermic than that of Na⁺?
- Give the expression for ΔStotal when a salt dissolves.
- Can a salt with an endothermic enthalpy of solution be soluble?
- What is the trend in solubility of Group 2 sulfates down the group?
- Why does the solubility of Group 2 sulfates decrease down the group?
- Why does the solubility of Group 2 hydroxides increase down the group?
Exam questions on Enthalpy of solution, hydration and solubility
- Sodium chloride dissolves in water: NaCl(s) + aq → Na⁺(aq) + Cl⁻(aq). Data (kJ mol⁻¹): lattice energy of NaCl −780 (formation of the solid from gaseous ions); enthalpy change of hydration of Na⁺ −406; enthalpy change of hydration of Cl⁻ −364.Calculate the enthalpy change of solution of sodium chloride.2 marks
- Magnesium chloride is used as a de-icing salt and dissolves in water: MgCl₂(s) + aq → Mg²⁺(aq) + 2Cl⁻(aq). Data (kJ mol⁻¹): lattice energy of MgCl₂ −2524; enthalpy change of hydration of Mg²⁺ −1920 and of Cl⁻ −364. For comparison, the lattice energy of NaCl is −780 and the enthalpy change of hydration of Na⁺ is −406. The ionic radius of Na⁺ is 0.102 nm and that of Mg²⁺ is 0.072 nm.Explain why the lattice energy of magnesium chloride is much more exothermic than that of sodium chloride.2 marks
- Magnesium sulfate (Epsom salts) dissolves readily in water, but barium sulfate is so insoluble that it can be swallowed as a 'barium meal' for X-ray imaging. Data (kJ mol⁻¹): lattice energy of MgSO₄ −2928 and of BaSO₄ −2423; enthalpy change of hydration of Mg²⁺ −1920, of Ba²⁺ −1305 and of SO₄²⁻ −1099; enthalpy change of solution of MgSO₄ −91.Calculate the enthalpy change of solution of barium sulfate.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).