Edexcel Jun 2014 (R) Paper 2 Q18 (with explained solutions) |

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Edexcel Jun 2014 (R) Paper 2 Q18

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18 This is a question about Group 2 elements and their compounds. *(a) Explain why the first ionization energy of calcium (590 kJ mol1) is greater than that of strontium (550 kJ mol1). (2)(b) (i) Describe how you would carry out a flame test on a sample of a Group 2 metal salt. (2)(ii) What result of the flame test would confirm the presence of a barium salt? (1)*(iii) Explain, in terms of electronic transitions, how the result of the flame test arises. (3)*P42991A01524* 15 Turn over<br />
(c) Barium reacts with water to form a clear, colourless solution. (i) Give the name or formula of the barium compound formed. (1)(ii) State another observation that would be made when barium reacts with water. (1)(d) Barium reacts with chlorine gas to form barium chloride as shown in the equation below. Ba(s) + Cl2(g) (cid:314) BaCl2(s) (i) Use the changes in oxidation numbers to show that this is a redox reaction. (2)(ii) Write the ionic equation for the reaction between barium chloride solution and dilute sulfuric acid. Include state symbols in the equation. (iii) The reaction in (d)(ii) is used to test for sulfate ions. Why is dilute hydrochloric acid added with the barium chloride solution in this test? (2) (1)16 *P42991A01624*<br />
(e) Magnesium carbonate, MgCO3, readily reacts with hydrochloric acid. (i) Write the equation for this reaction. State symbols are not required. (1) *(ii) The rate of the reaction between powdered magnesium carbonate and dilute hydrochloric acid was monitored using the experimental apparatus shown below. State two factors that would decrease the rate of this reaction, other than by changing the reaction temperature. Explain how these two factors decrease the reaction rate. (4) Factor 1Explanation 1Factor 2Explanation 2*P42991A01724* 17 Turn over<br />
(f) Suggest why pressure has little or no effect on the rate of the reaction of magnesium oxide and hydrochloric acid, the equation for which is given below. MgO(s) + 2HCl(aq) (cid:314) MgCl2(aq) + H2O(l) (1)(Total for Question 18 = 21 marks) TOTAL FOR SECTION B = 38 MARKS 18 *P42991A01824*<br />

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Acceptable Answers Question Number 18 (b)(i) Nichrome wire / platinum wire / silica rods (1) (Dip / clean) in (concentrated) HCl/HCl(aq)/dilute HCl and place in Bunsen flame (1) OR Allow alternative procedures such as: Make a salt solution (1) Soak in wooden splint and place in Bunsen flame (1) Mark Reject Nickel/Ni/ Chromium/Cr/ Metal loop/wire Yellow flame/burn Question Number 18 (a) Acceptable Answers The outer electrons are closer to the nucleus/smaller atomic radius/ less electron shells (in calcium) (1) Less shielding (in calcium) (1) OR Reverse argument for strontium Ignore reference to repulsion between shells Reject Mark Ionic radius/ Molecules Just less electrons Question Number 18 (b)(ii) Acceptable Answers Reject (Pale/Light) green / apple green Blue-green Mark 6CH0201R 1406<br />
Question Number 18 (b)(iii) Question Number 18 (c)(i) Question Number 18 (c)(ii) Question Number 18 (d)(i) Question Number 18 (d)(ii) Acceptable Answers Reject Mark Electrons promoted to higher energy level (1) Electron(s) return to lower energy level (1) Release of (visible/ light) energy/ photon upon return (1) Proton Acceptable Answers Barium hydroxide / Ba(OH)2 Allow product as part of the equation: Ba + 2H2OBa(OH)2 + H2 Acceptable Answers Bubbles / Fizzing / Effervescence IGNORE The Barium dissolves / forms a colourless solution Increase in temperature Reject Mark Mark Reject The metal sinks Air bubbles Just a gas is produced Mark Mark Acceptable Answers Reject Barium is oxidized from 0 to +2 (1) Chlorine is reduced from 0 to -1 (1) Allow one mark if oxidized and reduced are the wrong way round Ignore reference to transfer of electron unless incorrect. Acceptable Answers 2-(aq) BaSO4(s) Ba2+(aq) + SO4 One mark for chemical symbols (1) One mark for state symbols (1) Allow one mark maximum for: BaCl2(aq)+ H2SO4(aq) BaSO4(s)+ 2HCl(aq) OR Ions not cancelled Reject BaSO4(aq) 6CH0201R 1406<br />
Question Number 18 (d)(iii) Question Number 18 (e)(i) Reject Just to remove other ions Reject Mark Mark Acceptable Answers To prevent formation of carbonate / sulfite / sulfate(IV) (precipitate) / to remove carbonate / sulfite / sulfate(IV) ions Acceptable Answers MgCO3 + 2HClMgCl2 + H2O + CO2 Ignore state symbols even if incorrect ALLOW MgCO3 + 2HClMgCl2 + H2CO3 6CH0201R 1406<br />
Question Number 18 (e)(ii) Question Number 18 (f) Acceptable Answers Marking Point 1 (Factor) Use larger lumps (1) Marking Point 2 (Explanation) Decreases surface area OR Fewer collisions between the reactants (1) Alternatively Marking Point 1 (Factor) Decreases surface area (1) Marking Point 2 (Explanation) Fewer collisions between the reactants (1) Marking Point 3 (Factor) Decrease concentration (of acid) (1) Marking Point 4 (Explanation) Fewer collisions between the reactants OR Fewer particles for the same volume (1) Explanation marking point only awarded for correct factor or a near miss. Mark Reject Just increased size of MgCO3 Just change in volume of acid Acceptable Answers Pressure only affects gaseous reactions/ There is no significant volume change/the liquids are incompressible Reject Mark TOTAL FOR Q18 = 21 MARKS TOTAL FOR SECTION B = 38 MARKS 6CH0201R 1406<br />

Question 17 18 19 20 21 22

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