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CIE Nov 2017 v2 Paper 4 Q2
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![PMT (a) When water is added to magnesium nitride, Mg3N2, the products are a white suspension of Mg(OH)2 and an alkaline gas. (i) Write an equation for this reaction.[1] (ii) A 2.52 g sample of Mg3N2 is added to an excess of water. Calculate the mass of Mg(OH)2 formed. mass of Mg(OH)2 =g [2] (b) State and explain how the solubility of the Group 2 hydroxides varies down the group.[4] (c) Magnesium hydroxide is sparingly soluble in water. The concentration of its saturated solution at 298 K is 1.7104 mol dm3. (i) Write an expression for the solubility product, Ksp, of Mg(OH)2. Ksp = (ii) Calculate the value of Ksp for Mg(OH)2 at 298 K and state its units. [1] Ksp =units[2]UCLES 2017 9701/42/O/N/17<br />
PMT (d) The temperature at which the Group 2 hydroxides and carbonates start to decompose increases down the group. Suggest an explanation for this trend in the decomposition temperature of the Group 2 hydroxides.[2] [Total: 12]UCLES 2017 9701/42/O/N/17 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2017_v2_QP_-_Paper_4_CIE_Chemistry_A-level_2-0.jpg)
![9701/42 Question Cambridge International AS/A LevelMark Scheme PUBLISHED Answer October/November 2017 Marks 2(a)(i) Mg3N2 + 6H2O3Mg(OH)2 + 2NH3 2(a)(ii) moles of Mg3N2 = 2.52 / 100.9 = 0.025 (0.0249) (moles of Mg(OH)2 = 0.075 (0.0749)) mass of Mg(OH)2 = (0.07558.3) = 4.37 g or 4.4 g 2(b) solubility increases (down the group) Hlatt and Hhyd both decrease / less exothermic / more endothermic but Hlatt decreases more (than Hhyd decreases) Hsol becomes more negative / more exothermic / less endothermic 2(c)(i) 2(c)(ii) Ksp = [Mg2+] [OH]2 Ksp = (1.7 x 104)(21.7104)2 = 2.01011 (1.971011) mol3 dm9 2(d) cations become bigger / ionic radius increases polarisation/distortion of anion / hydroxide ion decreasesUCLES 2017 Page 3 of 12<br />](https://learnah.org/wp-content/uploads/2018/08/November_2017_v2_MS_-_Paper_4_CIE_Chemistry_A-level_2.jpg)