> A A-Level Chemistry Paper 1 MS 2020

Document Content and Description Below

Annotation Meaning Correct response Incorrect response Omission mark Benefit of doubt given Contradiction Rounding error Error in number of significant figures Error carried forward Level 1 ... Level 2 Level 3 Benefit of doubt not given Noted but no credit given Ignore Blank page Abbreviations, annotations and conventions used in the detailed Mark Scheme (to include abbreviations and subject-specific conventions). Annotation Meaning DO NOT ALLOW Answers which are not worthy of credit IGNORE Statements which are irrelevant ALLOW Answers that can be accepted ( ) Words which are not essential to gain credit __ Underlined words must be present in answer to score a mark ECF Error carried forward AW Alternative wording ORA Or reverse argument H432/01 Mark Scheme November 2020 5 SECTION A Question Answer Marks AO element Guidance 1 D 1 2.7 2 B 1 1.2 3 B 1 2.2 4 C 1 2.2 5 A 1 1.1 6 A 1 2.2 7 D 1 1.1 8 D 1 2.6 9 B 1 2.6 10 C 1 1.2 ALLOW 2 in the answer box 11 D 1 2.2 12 C 1 2.6 13 B 1 1.1 14 D 1 1.2 ALLOW 1 in the answer box 15 C 1 1.1 Total 15 H432/01 Mark Scheme November 2020 SECTION B Question Answer Marks AO element Guidance 16 (a) (The mean/average mass) taking into account the relative abundancies of the isotopes  1 1.1 ALLOW sum of (isotopic mass × %abundance) sum of (isotopic mass × abundance) / total abundance DO NOT ALLOW average mass of the isotopes (i) 2+ – Mg Br – Br Mg with no (or 8) outer electrons AND 2 × Br with ‘dot-and-cross’ outer octet  Correct charges  2 1.2 2.5 ALLOW 8 electrons in Mg2+ BUT ‘extra’ electron in Br– must match symbol for electrons in Mg2+ IGNORE inner shells and circles ALLOW 1 mark if both electron arrangements and charges are correct but only one Br is drawn. ALLOW 2[Br–], 2[Br] – (brackets not required) (ii) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 1.71 × 1022 award 3 marks ------------------------------------------------------------------------- n(MgBr2) = 1.74 184.1 = 0.00945….. mol  Moles of ions = 0.00945…. × 3 = 0.0283…. mol  Number of ions = 0.0283... × 6.02 × 1023 = 1.71 × 1022  3SF required 3 2.2×3 ALLOW ECF Calculator answer = 9.451385117 × 10–3 ALLOW ECF from incorrect moles of ions. e.g. 0.00945 Common error 5.69 × 1021 no × 3 2 marks x x H432/01 Mark Scheme November 2020 7 Question Answer Marks AO element Guidance (c)* Refer to marking instructions on page 5 of mark scheme for guidance on marking this question. Level 3 (5–6 marks) Explains all three melting point values and conductivities in terms of structure, bonding, particles and relative strengths of the forces. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Level 2 (3–4 marks) Attempts to explain all three melting point values and conductivities in terms of the structure, bonding, particles of all three substances, but explanations may be incomplete or may contain only some correct statements or comparisons. OR Correctly explains two of the melting point values and conductivities in terms of the structure, bonding, particles. There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence. Level 1 (1–2 marks) Identifies only some of the structures, forces and particles AND Attempts to explain the melting point values OR conductivities in terms of the structure, bonding, particles There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant. 0 marks No response or no response worthy of credit. 6 1.1×3 2.1×3 Indicative scientific points may include: Structure and bonding Magnesium • Structure: giant lattice • Metallic bonding • Delocalised electrons Bromine • Structure: simple molecular • induced dipole dipole forces (London forces) • (Between) molecules DO NOT ALLOW (between) atoms Magnesium bromide • Structure: giant lattice • Ionic bonding • (Between) oppositely charged ions Comparison of bond strengths • Metallic and ionic bonds are stronger than London forces OR Metallic and Ionic bonds need more energy to break than London forces Conductivity • Magnesium: conducts due to delocalised electrons can move/mobile. IGNORE ‘Carry’ charge for movement • Magnesium bromide: In solid IONS cannot move; in solution IONS can move. DO NOT ALLOW electrons. • Bromine: Does not conduct as no mobile charge carriers. H432/01 Mark Scheme November 2020 8 Question Answer Marks AO element Guidance (d) (i) Mg2+(g) + 2Br(g) + 2e– Mg(s) + Br2(l)  2 1.2× 2 State symbols required. CARE: Liquid state symbol for Br2 (ii) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = –346.5 award 2 marks ----------------------------------------------------------------- 2∆H hyd = – 525 – 186 – (2 x 112) – 148 – 736 – 1450 + (2 x -325) + 1926 OR – 525 – 186 – 224 – 148 – 736 – 1450 + 650 + 1926 OR = – 693  ∆H hyd = –346.5 (kJ mol–1)  2 2.2×2 ALLOW -347 (kJ mol–1) for 2 marks. ALLOW for 1 mark ONE error with sign OR use of 2: –693 (not divided by 2 at the end) 346.5 (wrong sign on answer) Common errors for 1 mark –2272.5 (–1926 instead of 1926) -1386 (2 x -693 instead of -693) –996.5 (–650 instead of 650) –509 (2 × 325 not used) –290.5 (2 × 112 not used) –198.5 (148 instead of –148) –160.5 (186 instead of –186) –122.5 (224 instead of –224) 178.5 (525 instead of –525) 389.5 (736 instead of –736) 1103.5 (1450 instead of –1450) For other answers, check for a single transcription error or calculation error which could merit 1 mark DO NOT ALLOW any answer which involves two errors e.g. –453 (2 × 325 not used AND 2 x 112 not used) H432/01 Mark Scheme November 2020 9 Question Answer Marks AO element Guidance (iii) Equation: Mg2+(g) + 2Br –(g) → MgBr2(s)  CHECK THE ANSWER ON ANSWER LINE If answer = –2433 award 2 marks ----------------------------------------------------------------- Lattice enthalpy = ∆hyH(Mg2+) + 2 × ∆hyH(Br–) – ∆solH(MgBr2) OR -1926 + (2 x -346.5) – (-186) OR ∆fH(MgBr2) – 2∆atH(Br) – ∆atH(Mg) – 1st IE(Mg) – 2nd IE(Mg) – 2∆eaH(Br) OR -525 – (2 x 112) – 148 – 736 – 1450 – (2 x -325)  Lattice enthalpy = –2433 kJ mol–1  3 1.2 2.2 x 2 State symbols required For other answers, check for a single transcription error or calculation error which could merit 1 mark DO NOT ALLOW any answer which involves two errors ALLOW ECF from incorrect answer to d(ii) [Show More]

Last updated: 3 years ago

Preview 1 out of 25 pages