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OCR A Jan 2013 Paper 1 Q4
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![The Group 2 element barium was first isolated by Sir Humphrey Davy in 1808. Barium has a giant metallic structure and a melting point of 725 C. (a) Describe, with the aid of a labelled diagram, the structure and bonding in barium and explain why barium has a high melting point. Include the correct charges on the metal particles in your diagram. In your answer, you should use appropriate technical terms, spelled correctly.[3] (b) A chemist reacts barium with water. A solution is formed which conducts electricity. (i) Write the equation for the reaction of barium with water. Include state symbols.[2] (ii) Predict a value for the pH of the resulting solution.[1] (iii) Give the formula of the negative ion responsible for the conductivity of the solution formed.[1] (c) Heartburn is a form of indigestion caused by an excess of stomach acid. State a compound of magnesium that could be used to treat heartburn.[1]OCR 2013<br />
(d) In an experiment, a student makes a solution of strontium chloride, SrCl2, by adding excess dilute hydrochloric acid to strontium carbonate. (i) Describe what the student would observe and write the equation for the reaction. observationsequation[2] (ii) Draw a dot-and-cross diagram to show the bonding of strontium chloride. Show outer electrons only. [2] (e) In another experiment, a student attempts to make a solution of strontium chloride by adding chlorine water to aqueous strontium bromide. (i) Describe what the student would observe.[1] (ii) Write the ionic equation for the reaction which takes place.[1] (iii) Chlorine is more reactive than bromine. Explain why.[4]OCR 2013 [Total: 18] Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JAN13_question_4-0.jpg)
![F321 Question 4 (a) Mark Scheme January 2013 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ Barium ion Answer(delocalised) electrons Diagram showing a regular arrangement of labelled Ba2+ ions or 2+ ions and some attempt to show electrons (cid:57) Scattering of labelled electrons between other species AND statement anywhere of delocalised electrons (can be in text or in diagram) (cid:57) The attraction between (positive) ions and (delocalised) electrons is strong (cid:57) Marks Guidance Regular arrangement must have at least two rows of correctly charged ions and a minimum of two ions per row ALLOW as label: positive ions, cations if correct charge is seen within circle ALLOW for labelled Ba2+ ions: circles with Ba2+ inside DO NOT ALLOW incorrect charge for ions eg + , 3+ etc DO NOT ALLOW for label of ions: nuclei OR positive atom OR protons ALLOW e or e oras symbol for electron within the lattice for first marking point if not labelled as electrons. ALLOW mobile or sea of for delocalised Quality of written communication: electron(s) spelled correctly and used in context for the third marking point ALLOW a lot of energy is needed to break OR overcome the attraction between (positive) ions and (delocalised) electrons IGNORE heat but ALLOW heat energy DO NOT ALLOW references to incorrect particles or incorrect attractions eg intermolecular attraction OR nuclear attraction IGNORE strong metallic bonds without seeing correct description of metallic bonding 11<br />
F321 Question 4 (b) Answer (i) Ba(s) + 2H2O(l) (cid:198) Ba(OH)2(aq) + H2(g) Ba(OH)2 as product (cid:57) Rest of equation + state symbols (cid:57) (ii) Any value or the range 7 < pH14 (cid:57) (iii) OH OR HO (cid:57) (c) Magnesium hydroxide OR magnesium oxide (cid:57) Mark Scheme January 2013 Marks Guidance ALLOW multiples DO NOT ALLOW if pH 7 is in a quoted range DO NOT ALLOW Ba2+ DO NOT ALLOW any reference to electrons ALLOW magnesium carbonate ALLOW correct formulae: Mg(OH)2, MgO, MgCO3 IGNORE milk of magnesia DO NOT ALLOW carbon dioxide produced without gas DO NOT ALLOW hydrogen gas produced OR any other named gas ALLOW it for strontium carbonate ALLOW strontium for strontium carbonate if SrCO3 seen in equation IGNORE reacts IGNORE references to temperature change IGNORE steam produced IGNORE state symbols (d) (i) Effervescence OR fizzing OR bubbling OR gas produced AND Strontium carbonate OR solid dissolves OR disappears OR a colourless solution is formed (cid:57) SrCO3 + 2HCl (cid:198) SrCl2 + H2O + CO2 (cid:57) 12<br />
F321 Question 4 (d) (ii) Answer 2+ Sr C l Cl Strontium ion with eight (or no) outermost electrons AND 2 x chloride (ions) with dot-and-cross outermost octet (cid:57) correct charges (cid:57) The mixture would turn orange (cid:57) (e) (i) (ii) Cl2 + 2Br (cid:198) Br2 + 2Cl (cid:57) 13 Mark Scheme January 2013 Marks Guidance For first mark, if eight electrons are shown in the cation then the extra electron in the anion must match symbol chosen for electrons in the cation IGNORE inner shell electrons Circles not essential ALLOW One mark if both electron arrangement and charges are correct but only one Cl is drawn ALLOW 2[Cl] 2[Cl] [Cl]2 (brackets not required) DO NOT ALLOW [Cl2] [Cl2]2 [2Cl]2- [Cl]2ALLOW shades and colours containing (eg dark orange, yellow-orange) ALLOW the following: yellow, yellow-brown, brown, brown-red BUT DO NOT ALLOW red alone IGNORE initial colours DO NOT ALLOW any response that includes precipitate OR solid ALLOW multiples IGNORE state symbols<br />
F321 Question 4 (iii) Mark Scheme January 2013 Marks Guidance Use annotations ie ticks crosses ECF ^ etc for this part Look for ORA from perspective of Br throughout. ALLOW all four marks applied to as you go up OR as you down the group ALLOW Cl for chlorine AND Br for bromine ALLOW ORA DO NOT ALLOW the use of ide BUT ALLOW use of ide as an ECF ALLOW chlorine is better at electron capture ALLOW chlorine has greater electron affinity IGNORE chlorine is more electronegative IGNORE chlorine has more oxidising power than bromine IGNORE explanations given in terms of displacement ALLOW chlorine has fewer shells ALLOW the electron is added to the (outer) shell closer to the nucleus IGNORE easily for greater or for stronger ALLOW chlorine has greater nuclear attraction (on its outermost electrons) OR (the outermost) electrons in chlorine are more attracted (to the nucleus) Answer The electron GAIN mark Chlorine will form a negative ion more easily than bromine OR Chlorine will gain an electron more easily than bromine (cid:57) Atomic size mark (An atom of) chlorine is smaller (than bromine) (cid:57) Shielding mark (Outermost shell of) chlorine is less shielded (than bromine) (cid:57) Stronger nuclear attraction mark Nuclear attraction (on the electron to be gained) by chlorine is greater (than bromine) OR the electron (to be gained) is attracted more strongly (to the nucleus) in chlorine (cid:57) Total 18 14<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JAN13_answer_4-0.jpg)
