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CIE Jun 2015 v3 Paper 2 Q2
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![The elements in Group II, and their compounds, show a variety of trends in their properties. (a) Magnesium, calcium and barium all react with cold water to form hydroxides. (i) Describe and explain the trend in reactivity of these three elements with cold water.[3] (ii) Give the equation for the reaction of magnesium with cold water.[1] (iii) Suggest why the water eventually turns cloudy during the reaction of magnesium with cold water.[1] (iv) Suggest the equation for the reaction of hot magnesium with steam.[1] (b) The oxides of magnesium, calcium and barium all react with dilute nitric acid to form nitrates. (i) Give the equation for the reaction of magnesium oxide with nitric acid.[1] (ii) State the trend in thermal stability of the nitrates of Group II.[1] (iii) Give the equation for the thermal decomposition of magnesium nitrate.[1]UCLES 2015 9701/23/M/J/15<br />
(iv) Apart from lithium nitrate, the nitrates of the Group I elements decompose in a different way to those of the Group II elements. The equation for the thermal decomposition of potassium nitrate is 2KNO32KNO2 + O2 By identifying any changes in oxidation number, explain which element is reduced and which is oxidised in this decomposition.[3] (c) A refractory material is one that does not decompose or melt at very high temperatures. Over 50% of magnesium oxide production is for use as a refractory material. Explain why magnesium oxide has a very high melting point.[2] (d) The word lime is usually used to refer to a range of calcium-containing compounds that have a range of uses. (i) Write equations to show how calcium carbonate can be converted into calcium hydroxide by a two-step process.[2] A garden pond, with a total volume of 8000 dm3, has been contaminated in such a way that its pH has fallen to 4. This means that the concentration of hydrogen ions, H+, in the water is 1104 mol dm3. (ii) Write an ionic equation for the neutralisation reaction that occurs between hydrogen ions and carbonate ions, CO3[1] 2. (iii) Use your equation to calculate the mass of powdered calcium carbonate that would need to be added to the pond to neutralise the acidity.UCLES 2015 9701/23/M/J/15 mass =g [2] [Total: 19] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v3_QP_-_Paper_2_CIE_Chemistry_A-level_2-0.jpg)
![Page 3 Question Cambridge International AS/A LevelMay/June 2015 9701 23 Mark Scheme Syllabus Paper Mark Scheme Mark Total (a) (i) Reactivity increases down the group OR reference to observations that indicate trend Outer electrons lost more easily down group Due to increased distance/shielding of outer electrons from nucleus (ii) Mg + 2H2O Mg(OH)2 + H2 (iii) Magnesium hydroxide sparingly soluble/insoluble (iv) Mg + H2O MgO + H2 (b) (i) MgO + 2HNO3 Mg(NO3)2 + H2O (ii) (thermal stability) increases down the group (iii) 2Mg(NO3)2 2MgO + 4NO2 + O2 (iv) N from (+)5 to (+)3 O from 2 to 0 N is reduced and O is oxidised (c) (Very) strong electrostatic attraction/ionic bond High charge (density) of cation and anion/Mg2+ and O2 (d) (i) CaCO3 CaO + CO2 CaO + H2O Ca(OH)2 (ii) 2H+ + CO3 2 CO2 + H2O (iii) 110 48000 = 0.8 mol H+100.1 = mass CaCO3 = 40 g 0.8 (a) (i) A/B = C = (ii) Chain (iii) Silver mirror/ppt/solid (black/grey) [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [3] [1] [1] [1] [1] [1] [1] [3] [2] [2] [1] [2] [19] [1] [1] [1] [1] [1] [3] [1] [1]Cambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v3_MS_-_Paper_2_CIE_Chemistry_A-level_2.jpg)