Edexcel Jun 2014 (IAL) Paper 2 Q20 (with explained solutions) |

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Edexcel Jun 2014 (IAL) Paper 2 Q20

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20 This question is about Group 2 elements and their compounds. *(a) Give two reasons why the first ionization energy of calcium is less than that of magnesium, even though the atomic number of calcium is greater than that of magnesium. (2)(b) A flame test was carried out on a solid calcium compound. Explain the origin of the flame colour in terms of electron movement. (3)(c) (i) Calcium oxide reacts with dilute nitric acid to form calcium nitrate. Write the equation for this reaction. State symbols are not required. (ii) Identify two ways, one of which should be an observation, in which the thermal decomposition of anhydrous calcium nitrate is different from that of anhydrous potassium nitrate. (1) (2)*P42977A01524* 15 Turn over<br />
(d) (i) Calcium reacts with water to produce calcium hydroxide and a gas. Give the name or formula of this gas. (1)(ii) An aqueous solution of calcium hydroxide is used for a common laboratory test. Give the observation for a positive result for this test and complete the equation for the reaction that occurs. State symbols are not required. (2) ObservationCa(OH)2 +(cid:314)+ H2O (iii) Give the name or formula of a Group 2 hydroxide which is more soluble than calcium hydroxide. (1)(e) (i) Describe what you would see if a solution of barium chloride was added to dilute sulfuric acid. State why this observation would differ if magnesium chloride solution was used instead of barium chloride. (2)(ii) Barium compounds are toxic. However, it is safe to give patients a barium meal of barium sulfate when trying to diagnose intestinal disorders. Suggest why this is so. (1)16 *P42977A01624*<br />
*(f) Calcium carbonate, CaCO3, readily reacts with hydrochloric acid. State two factors, other than a change in temperature, which would affect the rate of this reaction. Neither pressure nor the use of a catalyst should be considered. Explain how each of the two factors you have chosen alters the reaction rate. (4)(g) Suggest why pressure has little or no effect on the rate of the reaction of calcium oxide and hydrochloric acid, the equation for which is given below. CaO(s) + 2HCl(aq) (cid:314) CaCl2(aq) + H2O(l) (1)(Total for Question 20 = 20 marks) TOTAL FOR SECTION B = 38 MARKS *P42977A01724* 17 Turn over<br />

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The outer electrons are further from the nucleus / the electron being removed is further from the nucleus/ larger atomic radius (in calcium) ALLOW Ca has one more shell/ more shells (of electrons) (1) More shielding (in calcium) (1) OR Reverse argument for magnesium ALLOW Discussion based on trend going down group without specifying Mg and Ca IGNORE repulsion between shells Acceptable Answers Question Number 20 *(a) These marks are independent Mark Reject Larger ionic radius (in Ca) Just Calcium is larger Reference to molecules, delocalised electrons Just Ca has more energy levels Two more shells Any reference to polarising power of ions WCH0201 1406<br />
Question Number 20 (b) Acceptable Answers Reject Mark Electrons are promoted/ jump / become excited to higher energy level (1) Electron(s) return/ fall back to lower energy level ALLOW to ground state (1) Release of (visible ) light (energy) upon return / energy is released in visible spectrum ALLOW release of photons upon return (1) Question Number 20 (c)(i) CaO + 2HNO3Ca(NO3)2 + H2O Acceptable Answers Ignore state symbols even if incorrect Reject Mark WCH0201 1406<br />
Question Number 20 (c)(ii) Acceptable Answers Reject Flame colours Reference to other incorrect products. (1) Observation mark: (Calcium nitrate) produces a brown/ red-brown gas ALLOW NO2 for gas Fumes for gas OR (Potassium nitrate) does not produce a brown gas IGNORE Oxygen is given off / Gas given off relights a glowing splint Second mark (can also be an observation): (Only calcium nitrate) produces the oxide OR (Only potassium nitrate) produces the nitrite OR calcium nitrate is less stable to heat OR potassium nitrate decomposes at a higher temperature/takes longer to produce oxygen (1) ALLOW Calcium nitrate produces a white solid and potassium nitrate produces a yellow solid as an alternative for either mark NOTE Reject comparisons with one correct and one incorrect statement (this applies to both marks) Mark WCH0201 1406<br />
Acceptable Answers Question Number 20 (d)(i) Hydrogen (gas) / H2 Reject Mark Question Number 20 (d)(ii) Question Number 20 (d)(iii) If name and formula are given both must be correct Acceptable Answers Reject Mark White solution / any solution produced White ppt/white solid/goes milky/goes cloudy/ white suspension (1) Ca(OH)2 + CO2CaCO3 + H2O (1) ALLOW Alternative answer White precipitate forms which dissolves with excess carbon dioxide (1) Ca(OH)2 + 2CO2Ca(HCO3)2 (1) Mark Acceptable Answers Reject (One of): Sr(OH)2/Ba(OH)2/Ra(OH)2 OR (One of):Strontium/Barium/Radium hydroxide If name and formula given then both must be correct SrOH/ BaOH/ RaOH Just Sr/ Ba/ Ra Mg(OH)2/MgOH/ magnesium hydroxide/ Be(OH)2/BeOH/ beryllium hydroxide WCH0201 1406<br />
Acceptable Answers Question Number 20 (e)(i) White ppt/solid ALLOW White crystals (1) (BaSO4 is insoluble but) MgSO4 is (very) soluble / MgSO4 gives a colourless solution/ MgSO4 gives no precipitate ALLOW BaSO4 does not dissolve TE on first mark if it stated that a precipitate formed even if colour is wrong/ missing (1) Mark Reject White ppt of BaCl2 / MgCl2 Extra observations eg effervescence Magnesium is soluble / barium is insoluble A precipitate of magnesium sulfate forms and then dissolves Just MgSO4 is more soluble / less insoluble Reference to solubility of chlorides There would be no reaction Question Number 20 (e)(ii) Acceptable Answers Reject Mark Just Barium Barium sulfate is not absorbed/ is insoluble IGNORE Comments on X-rays Barium sulfate is not digested Barium sulfate is unreactive/ does not react with stomach acids References to toxicity. WCH0201 1406<br />
Question Number 20 (f) Mark Acceptable Answers Reject First mark: (Increase) concentration of HCl (1) Second mark More particles/ moles of (HCl) in the same volume OR more (frequent/ successful ) collisions Allow second mark only if factor is concentration (1) ------------------------------- Any two from three of the following for third and fourth marks: Reduce particle size / use powder (instead of lumps)/ use finely divided (solid) (1) (Increases) surface area (1) more (frequent/ successful ) collisions (1) ALLOW Reverse arguments Increase concentration of CaCO3 /HCl and CaCO3 /reactants Increase kinetic energy of particles Increase kinetic energy of particles WCH0201 1406<br />
Question Number 20(g) Reject Mark Acceptable Answers Pressure only affects gaseous reactions/ there are no gaseous reactants (or products) /there is no significant volume change/ liquids are incompressible ALLOW pressure doesnt affect solids/ solutions Note: there are many possible correct ways of expressing the idea that pressure only affects rate of reactions involving gases. IGNORE Number of moles in reaction doesnt change TOTAL FOR Q20 = 20 MARKS TOTAL FOR SECTION B = 38 MARKS WCH0201 1406<br />

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