NYGH 2016-S3MYE-IP Chem Ans

1 Nanyang Girls’ High School Secondary Three Chemistry (IP) – Mid Year Examination – 2016 Mark Scheme Section A Q1 C Q2 A Q3 B Q4 D Q5 C Q6 A Q7 B Q8 C Q9 A Q10 C Q11 D Q12 A Q13 A Q14 A Q15 B Q16 D Q17 B Q18 C Q19 C Q20 D Note: The correct chemical formula should be accepted when the question asks for the name of a chemical. The name of a chemical is should not be accepted when the question asks for the formula. If the question does not specify whether the name or formula of a chemical should be given, then either is acceptable. Section B B1. (a) Diffusion. [1] (b) Pb2+ / lead(II) ion has a higher relative atomic mass than I– / iodide ion and therefore diffuses / moves / travels more slowly. [1] or I– / iodide ion has a lower relative atomic mass than Pb2+ / lead(II) ion and therefore diffuses / moves / travels faster. [1] (c) The precipitate would be slightly to the right of the centre line / closer to Y. [1] or The precipitate would form more quickly / in a shorter time. [1] (d) The precipitate will take longer than 90 seconds to form. [1] Total [4] B2. (a) The solutions are very pale in colour / colourless. [1] (b) Sn2+, Cu2+ and Pb2+. [1] (c) No. Electrode B contains Ni2+ which is not present in electrode A. [1] or No. Electrode A does not contain Ni2+ which is present in electrode B. [1] (d) Spot should be drawn at 9 cm. [1] Total [4]

2 B3. (a) 40.0 cm3 [1] (b) After the sodium hydroxide has neutralised the acid, the pH increases above 7. [1] (c) The initial / starting pH of the acidic solution is 3, which is typical for a weak acid. [1] (d) (i) Methyl orange, litmus and phenolphthalein. At least two indicators. [1] (ii) Phenolphthalein only. [1] (e) H+(aq) + OH–(aq) → H2O(l) must have state symbols. [1] Total [6] B4. (a) Cu2+ / copper(II) ion, Fe2+ / iron(II) ion, Fe3+ / iron(III) ion. [1] (b) Silver chloride. Accept AgCl (formula must be correct). [1] (c) Lead(II) chloride / PbCl2 is insoluble in water. [1] (d) Aluminium hydroxide. Accept Al(OH)3 (formula must be correct). [1] (e) Al3+ [1] Cl– [1] (f) AlCl3(aq) + 3NaOH(aq) → Al(OH)3(s) + 3NaCl(aq) [1] Note: Question asks for state symbols – no mark awarded if state symbols not given. (g) Ag+(aq) + Cl–(aq) → AgCl(s) must have state symbols. [1] Total [8] B5. (a) (i) Covalent bonding [1] Noble gas electronic configurations [1] (ii) Sulfur dichloride has a simple covalent structure / is a simple covalent compound. There are weak intermolecular forces of attraction / van der Waal’s forces of attraction between the molecules [1] which only require a small amount of energy / low temperature to weaken. [1]

3 (b) (i) Ionic bonding [1] Noble gas electronic configurations [1] (ii) Magnesium chloride has a giant ionic lattice. All of the ions are held in a fixed position by strong electrostatic forces of attraction in the solid state [1] and are unable to conduct electricity. Only when liquid / molten are ions free to move / mobile to the electrode of opposite charge. [1] Total [8] Section C C1. (a) Pure dry oxalic acid does not contain H+ / hydrogen ions in solution. [1] (b) A weak acid does not fully ionise, when dissolved in water, to produce H+ ions / hydrogen ions (as the only positive ion). [1] (c) (i) H2C2O4(aq) + 2NaOH(aq) → Na2C2O4(aq) + 2H2O(l) Ignore state symbols. [1] (ii) Soluble. All sodium salts are soluble in water. [1] (d) (i) Any soluble calcium salt, e.g. calcium chloride or calcium nitrate. [1] (ii) Mix the aqueous reagents together. Filter the mixture to obtain the precipitate / residue. [1] Wash the residue with (cold) distilled water. [1] Dry the residue by pressing between layers of filter paper. [1] (e) (i) K2SO4 [1] (ii) 10 [1] Total [10]