O-LevelChemistryMetals & Reactivity5070/22 · Oct/Nov 2016 · Q910 Marks

Both copper and magnesium are metals.

(a)Explain why magnesium reacts with hydrochloric acid but copper does not.[1]
(b)Brass is an alloy of copper and zinc. The table shows how the composition of brass influences its relative strength. composition of brass | relative strength % copper | % zinc ---|---|--- 90 | 10 | 2.6 80 | 20 | 3.0 70 | 30 | 3.3 60 | 40 | 3.6 How does the composition of brass affect its strength?[1]
(c)Use your knowledge of the structure of metals to explain why brass is stronger than pure copper. You may include a labelled diagram in your answer.[3]
(d)Draw a labelled diagram to show how a steel rod can be electroplated with copper.[3]
(e)A 11.09 g sample of an oxide of copper contains 9.86 g of copper. Deduce the empirical formula of this oxide of copper. empirical formula[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2016). The mark or mark type is shown in brackets.

[1] magnesium loses (outer shell) electrons more easily than copper/copper cannot give (outer shell) electrons to hydrogen ions but magnesium can ORA
[1] the more zinc the greater the strength/the more copper, the lower the strength
[1] layers (of atoms/ions) in copper can slide (when a force is applied)
[1] atoms/ions of zinc are different size to those of copper/atoms of zinc disrupt the copper lattice
[1] layers (of atoms/ions) in alloy cannot slide (as easily)
[1] two rods dipping into a liquid and joined to a power supply
[1] electrolyte labelled as 'aqueous copper ions'/named solution of soluble copper salt e.g. aqueous copper sulfate/solution of copper sulfate
[1] copper anode/positive electrode AND steel cathode/ negative electrode
[2] Cu2O
[1] If two marks not scored, mol Cu = 9.86/64 AND mol O = 1.23/16 scores 1 mark

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