NewcastleCHEM AQAAQA-74051-QP-JUN17

This question is about silver iodide. 0 1 . 1 Define the term enthalpy of lattice formation. [2 marks] 0 1 . 2 Some enthalpy change data are shown in Table 1. Table 1 Enthalpy change / kJ mol−1 AgI(s) → Ag+ (aq) + I– (aq) +112 Ag+ (g) → Ag+ (aq) −464 I – (g) → I – (aq) −293 Use the data in Table 1 to calculate the enthalpy of lattice formation of silver iodide. [2 marks] Enthalpy of lattice formation kJ mol−1 3 *03* Turn over ► IB/M/Jun17/7405/1 Do not write outside the box 0 1 . 3 A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the value calculated in Question 1.2 Explain this difference. [2 marks] 0 1 . 4 Identify a reagent that could be used to indicate the presence of iodide ions in an aqueous solution and describe the observation made. [2 marks] Reagent Observation Turn over for the next question 8 4 *04* IB/M/Jun17/7405/1 Do not write outside the box 0 2 This question is about acidic solutions. 0 2 . 1 The acid dissociation constant, Ka, for ethanoic acid is given by the expression Ka = [CH COOH] [CH COO ] [H ] 3 3 − + The value of Ka for ethanoic acid is 1.74 × 10−5 mol dm−3 at 25 °C A buffer solution with a pH of 3.87 was prepared using ethanoic acid and sodium ethanoate. In the buffer solution, the concentration of ethanoate ions was 0.136 mol dm−3 Calculate the concentration of the ethanoic acid in the buffer solution. Give your answer to three significant figures