A Level Chemistry A H432 Q3 MS

Question Answer Marks AO element Guidance 1 (a) (i) Water flow AND condenser Water in at bottom and out at top AND condenser  Flask and technique Pear-shaped/round-bottom flask AND reflux  2 1.2 × 2 DO NOT ALLOW conical flask, volumetric flask, beaker in place of round bottom/pear shaped flask Pear-shaped / Round-bottom flask H432/03 Mark Scheme Oct 2020 7 Question Answer Marks AO element Guidance (ii) Diagram showing knowledge of filtration under reduced pressure Diagram showing Buchner flask must have ONE side arm AND Buchner/Hirsh funnel on top of flask  Labels not required ---------------------------------- Further details: • Funnel sealed or stoppered to flask AND • Apparatus capable of filtering under reduced pressure AND • Label for setup from side arm to indicate reduced pressure AND • Label for Buchner flask OR Buchner/Hirsh funnel  ALLOW slips in spelling of ‘Buchner’ 2 2.3 2.7 Labels NOT required for diagram ALLOW diagram of a conical flask with a filtering setup above AND Side arm either in conical flask OR between flask and filter paper of funnel IGNORE absence of seals ---------------------------------- MUST imply some type of seal between filter setup and flask. ALLOW small gaps Examples of suitable labels (may have arrow from side arm or tube attached) • to pump • to vacuum • air out • suction • reduced pressure • etc. For Buchner flask and Buchner funnel DO NOT ALLOW just ‘flask OR ‘funnel’ Flask and funnel used in normal filtration H432/03 Mark Scheme Oct 2020 8 Question Answer Marks AO element Guidance (b) (i) Comparison of branching and points of contact e.g. CH3CH2CH2NH2 has longer chain / straight chain / no branches AND e.g. CH3CH2CH2NH2 has more points of contact / more surface interaction (between molecules)  Relative strength of force e.g. CH3CH2CH2NH2 has stronger/more induced dipole(–dipole) interactions OR London forces  -------------------------------------------------------------- Hydrogen bonds CH3CH2CH2NH2 OR (CH3)2CHNH2 have hydrogen/H bonds OR (CH3)3N has no hydrogen/H bonds  Relative strength of force Hydrogen bonds are stronger than London forces /permanent dipole interactions  ------------------------------------------------------------------ Comparison of energy required to break force e.g. More energy to break/overcome London forces/intermolecular forces in CH3CH2CH2NH2 OR More energy is needed to break H bonds (than London forces)  5 → 4 max 1.2 2.1 1.2 2.1 ANNOTATE WITH TICKS AND CROSSES, etc. ------------------------------------------------------------------ ALLOW ORA throughout ALLOW ‘The straighter the chain, the more points of contact ….’ IGNORE comparison using ‘primary’, ‘secondary’ and ‘tertiary’. Comparison of branching is required. For London forces, • ALLOW induced dipole(–dipole) interactions • IGNORE IDID OR van der Waals’ forces/VDW DO NOT ALLOW CH3CH2CH2NH2 has more electrons (number of electrons are the same) DO NOT ALLOW ‘more energy to break covalent bonds ALLOW little energy is required to break London forces (compared with H bonds) H432/03 Mark Scheme Oct 2020 9 Question Answer Marks AO element Guidance (b) (ii) FIRST CHECK MOLECULAR FORMULA and STRUCTURE IF molecular formula = C5H13N AND correct structure AND evidence of ideal gas equation → 6 marks Correct up to 87 AND C5H13N → 5 marks Correct up to 87 → 4 marks -------------------------------------------------------------------------- Rearranging ideal gas equation n = pV RT  Unit conversion AND substitution into n = pV RT : • R = 8.314 OR 8.31 • V = 72(.0) × 10–6 • T in K: 373 K e.g. 1.00 × 105 × 72.0 × 10–6 8.314 × 373  Calculation of n n = 2.32 × 10–3 (mol)  Calculation of M M = 0.202 2.32 × 10–3 = 87  Molecular formula C5H13N  Molecular formula required 6 2.2×4 3.2 IF n = pV RT is omitted, ALLOW when values are substituted into rearranged ideal gas equation. Calculator: n = 2. × 10–3 from 8.314 From 8.31, n = 2. × 10–3 ALLOW elements in any order ALLOW molecular formula = C3H9N3 ALLOW other molecular formulae of an amine that has M = 87, e.g. C4H9NO H432/03 Mark Scheme Oct 2020 10 Question Answer Marks AO element Guidance Structure of amine A from C5H13N  OR OR OR OR 3.2 ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous ALLOW structures below from molecular formula = C3H9N3 ALLOW ECF but only if structure has calculated Mr AND has 3 peaks in 13C NMR spectrum. Use of 24000 3 marks max possible for use of 72.0 cm3 OR 0.720 dm3 by ECF Calculation e.g. n = 72.0 24000 = 3.00 × 10–3 No mark (calculation much simpler) M = 0.202 3.00 × 10–3 = 67.3 OR 67  ECF Molecular formula = C4H5N  ECF Structure  ECF H432/03 Mark Scheme Oct 2020 11 Question Answer Marks AO element Guidance (c) Organic product and water marked independently. 1st mark correct organic product OR water IGNORE balancing numbers 2nd mark BOTH products AND correctly balanced. 2 3.2 ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous ALLOW NOTE: For ECF, any structure must have correct number of bonds to C, H, O and N DO NOT ALLOW structure of dimer Question states molecular formula = C3H3NO Total 16   H432/03 Mark Scheme Oct 2020 12 Question Answer Marks AO element Guidance 2* Refer to marking instructions on page 5 of mark scheme for guidance on marking this question. Level 3 (5-6 marks) Comprehensive explanation of the terms, ligand and coordination number and ligand substitution AND 3D diagrams of suitable examples of 6 AND 4 coordinate complex ions with different shapes AND Ligand substitution illustrated with a balanced equation 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) Explanation of the terms, ligand and coordination number and ligand substitution with some errors or omissions AND: Diagrams of suitable examples of 6 AND 4 coordinate complex ions with different shapes OR A 3D wedged diagram of a suitable example of 6 OR 4 coordination OR A diagram of a suitable example of 6 OR 4 coordination AND ligand substitution illustrated with an equation OR Ligand substitution illustrated with a balanced equation There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence 6 1.1×4 2.1×2 Indicative scientific points may include: Terms • Ligand: Donates a lone pair to metal ion Forms dative covalent (coordinate) bond with metal ion • Coordination number: Number of coordinate bonds to metal ion. Could be implicit in annotated diagrams NOTE: For monodentate ligands, ‘number of ligands’ is the same as the number of coordination number • Ligand substitution: One ligand replacing another Suitable examples of complex ions with different shapes • Coordination no 6 Octahedral e.g. [Cu(H2O)6] 2+, [Fe(H2O)6] 3+ • Coordination no 4 Tetrahedral e.g. CuCl4 2– , CoCl4 2– OR Square planar Pt complexes, e.g. Pt(NH3)2Cl2 Diagrams and equations • Diagrams of complex ions (may be 3D) • Equation for ligand substitution e.g. [Cu(H2O)6] 2+ + 4Cl– → CuCl4 2– + 6H2O [Cu(H2O)6] 2+ + 4NH3 → [Cu(NH3)4(H2O)2] 2+ + 4H2O NOTE: A clear and logically structured response would link shapes with some of: coordination number, names of shapes, connectivity, involvement of lone pairs, bond angles, etc. (not inclusive) ALLOW minor slips NOTE: Levels and the mark within a level is a ‘best-fit’, not perfection H432/03 Mark Scheme Oct 2020 13 Question Answer Marks AO element Guidance Level 1 (1-2 marks) Explanation of some terms: ligand, coordination number and ligand substitution with some errors or omissions. AND A suitable example of a complex ion OR Ligand substitution illustrated with an equation with some errors 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