OCR A Jun 2011 Paper 1 Q4 (with explained solutions) |

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OCR A Jun 2011 Paper 1 Q4

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4 Many metallic elements react with dilute hydrochloric acid to form a solution containing a salt. 10 (a) Zinc reacts with dilute hydrochloric acid to form a solution of the salt, zinc chloride, ZnCl2. Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) (i) Explain why ZnCl2 is a salt.[1] (ii) Predict the formula of the zinc salt that could be formed by adding an excess of zinc to phosphoric(V) acid, H3PO4.[1]OCR 2011<br />
(b) Group 2 elements also react with dilute hydrochloric acid. 11 Describe and explain the trend in reactivity of the Group 2 elements with dilute hydrochloric acid as the group is descended. In your answer you should use appropriate technical terms, spelled correctly.[5] [Total: 7]OCR 2011 Turn over<br />

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F321 Question Answer 4 (a) (i) The hydrogen ions OR H+ OR protons (of hydrochloric acid) are replaced by zinc ions OR Zn2+ (cid:57) Mark Scheme June 2011 (ii) Zn3(PO4)2 (cid:57) (b) reactivity increases (down the group) (cid:57) Increasing size mark atomic radii increases OR there are more shells (cid:57) Increased shielding mark there is more shielding (cid:57) Nuclear attraction mark The nuclear attraction decreases OR (outermost) electrons experience less attraction (to nucleus) OR Increased shielding / distance outweighs the increased nuclear charge (cid:57) easier to remove (outer) electrons OR ionisation energy decreases (cid:57) ORA throughout Total Guidance ALLOW Zn ions OR positive ions replace H ions OR a metal ion has replaced a hydrogen ion OR protons DO NOT ALLOW Zn replaces H. Ions are key either in word form or symbol form DO NOT ALLOW Zn+ i.e. if charge is shown it must be correct ALLOW ZnHPO4 OR Zn(H2PO4)2 ALLOW Zn3P2O8 USE annotations with ticks, crosses, con, ECF, etc for this part. down the group not required ALLOW alternative phrases for reactivity increases ALLOW there are more energy levels ALLOW electrons are in a higher energy level ALLOW the electrons are further from nucleus IGNORE there are more orbitals OR more sub-shells IGNORE different shell or new shell ALLOW more screening There must be a clear comparison i.e. more shielding OR increased shielding. i.e. DO NOT ALLOW there is shielding ALLOW there is more electron repulsion from inner shells more is essential ALLOW there is less nuclear pull OR electrons less tightly held IGNORE there is less effective nuclear charge IGNORE nuclear charge for nuclear attraction ALLOW easier to oxidise Quality of Written Communicationelectron(s) OR ionisation OR ionization OR oxidise OR oxidize spelled correctly at least once for 5th marking point Mark 1 1 1 1 1<br />

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