June 2016: AS Paper 2, Depth in chemistry

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Notes from the mark scheme and report

• ALLOW upper case S and P, and subscripts

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Notes from the mark scheme and report

• must say TWO electrons lost
• IGNORE reference to oxidation numbers

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Notes from the mark scheme and report

• starts from Sr+(g) not Sr(g)
• state symbols required
• IGNORE states on the electron

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Notes from the mark scheme and report

• comparison needed for each mark
• IGNORE more orbitals/sub-shells
• IGNORE nuclear charge alone - increased nuclear charge must be outweighed by distance/shielding

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Notes from the mark scheme and report

• DO NOT ALLOW volumetric flask, beaker or measuring cylinder as reaction vessel
• DO NOT ALLOW delivery tube below reacting solution
• closed system with labelled gas syringe or collection over water

Skills: PAG1 Moles determination

Mark scheme

Notes from the mark scheme and report

• DO NOT ALLOW pV = nRT for moles (RTP so 24 000 cm3)
• DO NOT ALLOW calcium with no working
• ALLOW ECF as Group 2 element closest to calculated value

Skills: M0.0 Recognise and make use of appropriate units in calculations; M0.2 Use ratios, fractions and percentages; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities; PAG1 Moles determination

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Notes from the mark scheme and report

• less volume AND fewer moles of metal
• IGNORE higher relative atomic mass alone

Skills: M0.2 Use ratios, fractions and percentages

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Notes from the mark scheme and report

• P4 has more electrons (DO NOT ALLOW more outer-shell electrons or larger electron cloud)
• IGNORE bigger molecules/greater Mr
• DO NOT ALLOW covalent bonds broken or attraction between atoms

Skills: M3.1 Translate information between graphical, numerical and algebraic forms

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Notes from the mark scheme and report

• Mg: cations and delocalised electrons (IGNORE 'sea of electrons')
• Si: covalent bonds between atoms
• DO NOT ALLOW molecules or intermolecular forces

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Notes from the mark scheme and report

• Al2S3 + 6H2O → 2Al(OH)3 + 3H2S
• IGNORE state symbols
• ALLOW multiples

Skills: M0.2 Use ratios, fractions and percentages

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Notes from the mark scheme and report

• σ direct/head-on overlap between nuclei, π sideways overlap above and below
• IGNORE bond length
• IGNORE type of orbital for σ bond

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Notes from the mark scheme and report

• one C of C=C has two identical (methyl) groups
• DO NOT ALLOW 'two groups on the same side'
• DO NOT ALLOW functional groups or molecules for groups

Mark scheme

Notes from the mark scheme and report

• mark independently
• DO NOT ALLOW –CH3CH2 connectivity
• DO NOT ALLOW trans-pent-2-ene

Skills: M4.2 Visualise and represent 2-D and 3-D forms including 2-D representations of 3-D objects

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Notes from the mark scheme and report

• 2-methylbutan-2-ol and 3-methylbutan-2-ol
• ALLOW any vertical bond to OH
• DO NOT ALLOW OH–

Mark scheme, with the levels and indicative points

Notes from the mark scheme and report

• two products 2-bromo-2-methylbutane and 2-bromo-3-methylbutane
• curly arrow from C=C to H of H–Br, dipole on H–Br, arrow from H–Br bond to Br, carbocation, arrow from Br– lone pair to C+
• major product from more stable tertiary carbocation

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Notes from the mark scheme and report

• more energy required for bond breaking than released by bond making

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Notes from the mark scheme and report

• products above reactants with upward ∆H arrow
• N2(g) + ½O2(g) → N2O(g) with state symbols
• DO NOT ALLOW multiples (1 mol N2O formed)
• IGNORE activation energy

Skills: M3.1 Translate information between graphical, numerical and algebraic forms

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Notes from the mark scheme and report

• common errors: no temperature conversion to K (3.05 × 10^5), dm3 not converted to m3 (4.46 × 10^3 or 10^9), no standard form
• must be standard form AND 3 SF
• ALLOW ECF from incorrect n(N2O)

Skills: M0.0 Recognise and make use of appropriate units in calculations; M0.1 Recognise and use expressions in decimal and ordinary form; M1.1 Use an appropriate number of significant figures; M2.2 Change the subject of an equation; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities

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Notes from the mark scheme and report

• NO• + O3 → NO2• + O2 then NO2• + O → NO• + O2
• one mark only if dots missing or extra

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Notes from the mark scheme and report

• CO2 lost as a gas
• DO NOT ALLOW water/steam or 'CO2 evaporates'

Skills: PAG9 Rates of reaction – continuous monitoring

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Notes from the mark scheme and report

• 2:1 ratio HNO3:SrCO3
• ALLOW ECF from incorrect n(HNO3) and n(SrCO3)

Skills: M0.0 Recognise and make use of appropriate units in calculations; M0.2 Use ratios, fractions and percentages; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities

Mark scheme

Notes from the mark scheme and report

• rate decreases AND concentration decreases
• less frequent collisions/fewer per unit time
• IGNORE 'less collisions' and 'less successful collisions'

Skills: M3.1 Translate information between graphical, numerical and algebraic forms

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Notes from the mark scheme and report

• tangent must be drawn at t = 200 s
• answer in range 5 × 10^-4 to 8 × 10^-4
• IGNORE units and sign

Skills: M3.1 Translate information between graphical, numerical and algebraic forms; M3.5 Draw and use the slope of a tangent to a curve as a measure of rate of change

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Notes from the mark scheme and report

• flask or beaker AND balance AND timer
• record mass at time intervals
• interval of 10–50 s quoted
• DO NOT ALLOW round-bottomed flask
• IGNORE weighing scales

Skills: PAG9 Rates of reaction – continuous monitoring

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Notes from the mark scheme and report

• C bearing –OH is attached to two C atoms/alkyl groups (or one H)

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Notes from the mark scheme and report

• 104.5° (ALLOW 104–105)
• two bonded pairs and two lone pairs
• lone pairs repel more than bonding pairs
• IGNORE 'bonds/electrons repel'
• DO NOT ALLOW atoms repel

Skills: M4.1 Use angles and shapes in regular 2-D and 3-D structures

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Notes from the mark scheme and report

• butanone structure
• ALLOW molecular formulae in equation

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Notes from the mark scheme and report

• butan-2-ol/butanone flammable or volatile so would evaporate (DO NOT ALLOW 'the product or reactant' unspecified)
• heat under reflux
• DO NOT ALLOW distillation
• DO NOT ALLOW closed system
• IGNORE vague health and safety

Skills: PAG5 Synthesis of an organic liquid

Mark scheme

Notes from the mark scheme and report

• common ECF: incorrect Mr of butan-2-ol (74) or 2-bromobutane (136.9)
• ALLOW 67% only if 67.4 shown in working

Skills: M0.2 Use ratios, fractions and percentages; M1.1 Use an appropriate number of significant figures; M2.3 Substitute numerical values into algebraic equations using appropriate units for physical quantities

Mark scheme, with the levels and indicative points

Notes from the mark scheme and report

• empirical formula C2H4O and M+ at 88 gives C4H8O2
• broad O–H 2500–3300 and C=O about 1700 so carboxylic acid
• m/z 43 is secondary carbocation (CH3)2CH+ so C is (CH3)2CHCOOH not butanoic acid
• IGNORE C–O peaks

Skills: M0.2 Use ratios, fractions and percentages; M3.1 Translate information between graphical, numerical and algebraic forms