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Oxford Cambridge and RSA Examinations

GCE

Chemistry A

H032/02: Depth in chemistry

Advanced Subsidiary GCE

Mark Scheme for June 2019

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This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by examiners. It does not indicate the details of the discussions which took place at an examiners’ meeting before marking commenced.

All examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated.

Mark schemes should be read in conjunction with the published question papers and the report on the examination.

© OCR 201 9

H032/02 Mark Scheme June 2019

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

H032/02 Mark Scheme June 2019

Subject-specific Marking Instructions

INTRODUCTION

Your first task as an Examiner is to become thoroughly familiar with the material on which the examination depends. This material includes:

• the specification, especially the assessment objectives
• the question paper
• the mark scheme.

You should ensure that you have copies of these materials.

You should ensure also that you are familiar with the administrative procedures related to the marking process. These are set out in the OCR booklet Instructions for Examiners. If you are examining for the first time, please read carefully Appendix 5 Introduction to Script Marking: Notes for New Examiners.

Please ask for help or guidance whenever you need it. Your first point of contact is your Team Leader.

H032/02 Mark Scheme June 2019

Question Answer Marks

AO

element Guidance 1 (b) Bonding and structure

• ion

electrons

Metallic bonding diagram Regular arrangement of labelled + ions 

scattering of labelled electrons between other species 

Properties linked to explanation metallic bond or attraction between the electrons and the positive ions/cations 

bonds are strong/require a lot of energy to break AND high melting point 

Delocalised electrons move AND good conductivity 

AO1.

×

Diagram must have at least two rows and a minimum of two ions per row (allow Sr +^ or Sr 2+)

ALLOW for labels: + ions, positive ions, cations

ALLOW e–^ OR e as label for electron

AO2.

×

DO NOT ALLOW intermolecular forces

ALLOW mobile electrons

(c) (i) Sr + 2H 2 O → Sr(OH) 2 + H 2  1 AO2.6 ALLOW correct multiples including fractions IGNORE state symbols

H032/02 Mark Scheme June 2019

Question Answer Marks

AO

element Guidance (c) (ii) Two points () from With calcium:

1. less vigorous fizzing/bubbling/effervescence 2. dissolves more slowly/slower reaction 3. solution has a lower pH/less alkaline 4. precipitate forms/less soluble

2 AO2.

× 2

IGNORE gives out less/more heat, less reactive, less gas

1 (d) (i) FIRST CHECK THE ANSWER ON ANSWER LINE 3 If answer = 5.8 award 3 marks

n (SrCl 2 ) =

= 0.0102……. (mol) 

AO3.

× 2

Calculator: 0.

n (H 2 O) =

= 0.0594……… (mol)  Calculator:^ 0. 18

x = SrCl 2 : H 2 O =

0.0594….. (^) ALLOW ECF from n (SrCl 2 ) and/or n (H 2 O)

0.0102…… AO3.2 Answer must be to^ TWO^ significant figures = 5.8  ALLOW 2 marks for 5.83 (answer must be to 2 SF)

H032/02 Mark Scheme June 2019

Question Answer Marks (^) elementAO Guidance 2 (a) Please refer to the marking instructions on page 4 of this 6 AO2.8 (^) Indicative scientific points may include:

Calculation: n =

× 0.4000 = 0.1(000) (mol) 1000

M (Mg(NO 3 ) 2 •6H 2 O) = 256. Mass = 0.1000 × 256.3 = 25.63 g

OR M (Mg(NO 3 ) 2 ) = 148. Mass = 14.83 g

ALLOW small slip/rounding errors such as errors on M r (e.g. use of 24 instead of 24.3 for Mg A r )

Preparation steps (apparatus and method):

• Weigh mass of crystals
• Dissolve in (distilled/deionised) water
• Transfer to 250 cm^3 volumetric flask
• Make up to the mark with more water so that bottom of meniscus is on the mark

IGNORE removing the water of crystallisation

Fine detail:

• 2 or more decimal place balance
• Rinse beaker and transfer washings to flask
• Use of dropping pipette when filling to mark
• Stopper, invert several times to mix

mark scheme for guidance on how to mark this question. ×

Level 3 (5–6 marks) Calculates the correct mass of Mg(NO 3 ) 2 •6H 2 O or Mg(NO 3 ) 2. AND Explains the preparation steps, with most fine detail.

There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated.

AO2.

×

Level 2 (3–4 marks) Attempts a calculation which is partly correct. AND Outlines the preparation steps, with some fine detail.

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) Attempts the calculation but makes little progress or

AO2.

×

makes errors. OR Briefly outlines the preparation steps, which may be incomplete

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.

H032/02 Mark Scheme June 2019

Question Answer Marks (^) elementAO Guidance 2 (b) FIRST CHECK THE ANSWER ON ANSWER LINE 3 AO2. If answer = 38.5 cm^3 award 3 marks ---------------------------------------------------------------------------

× 3

n (Mg(NO 3 ) 2 ) =

= 0.0337 .......... (mol)  Calculator : 0.

n (HNO 3 ) = 2 × 0.0337 …….. = 0.0674 .............(mol)  ALLOW ECF^ from^ n (Mg(NO^3 )^2 ) Calculator : 0. volume = 0.0674…….. ×

= 38.5 (cm^3 )  1.75 ALLOW ECF^ from^ n (HNO^3 ) 3 SF required (c)

Element oxidised : Oxygen/O Change from: –2 to 0 

Element reduced : Nitrogen/N: Change form + 5 to +4 

2 AO2.

× 2

MAX 1 mark if no ‘+’ sign for oxidation number

ALLOW 2–

ALLOW 5+ AND 4+

ALLOW O 2 for oxygen

ALLOW 1 mark for all oxidation numbers correct, but oxidised and reduced the wrong way around

IGNORE numbers around equation i.e. treat as rough working

Total 11

H032/02 Mark Scheme June 2019

3 (a) (iii) (^) C–I bond is weaker (than C–Br bond) OR C–I bond has a lower bond enthalpy (than C–Br bond) 

Carbon – halogen bond breaks 

2 AO3.2 For 2 marks, ALLOW C–I is broken more easily (than C–Br) as the bond is weaker

There must be a comparison between C–Br and C–I bonds

(b) (i) (^) Molecular mass  (^1) AO1.1 IGNORE ‘relative’ IGNORE ‘molecular ion’ alone, answer must relate to mass

ALLOW M r / molar mass

(ii)

Y : CH 3 CH 2 CH 2 CH 2 CH 2 

Z : CH 3 CH 2 CH 2 +^ 

If positive charge is missing but the structures of Y AND Z are correct, award one mark

2 AO3.

× 2

FOR ONE MARK

ALLOW C 5 H 11 +^ AND C 3 H 7 +

ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous

(c) (i)

1 AO1.1 ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous

(ii) Similarity Both have a peak at ( m / z = ) 198 (X) OR 71 (Y) OR 29 

Difference 2-iodo-2-methylbutane has no peak at ( m / z =) 43 (Z) 

2 AO3.

× 2

ALLOW same molecular ion peak / M r

IGNORE statements where no specific ion peak is suggested e.g. “different ion peaks” Total 12

H032/02 Mark Scheme June 2019

Question Answer Marks (^) elementAO Guidance

4 (a) FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 60 cm 3 award 3 marks --------------------------------------------------------------------------- n (HCl) =

× 0.100 = 5.00 × 10–3^ (mol)  1000

n (H ) =

5.00 × 10–

= 2.50 × 10–3^ (mol) 2 2 

Volume = 2.5(0) × 10–3^ × 24.0 × 1000 = 60(.0) cm^3 

3 AO2.

× 3

ALLOW 120 cm^3 for 2 marks (no ÷ 2) ALLOW 240 cm^3 for 2 marks (× 2 not ÷ 2)

IGNORE absence of trailing zeroes, e.g. for 0.100, ALLOW 0.

ALLOW ECF from n (HCl)

ALLOW ECF from n (HCl) and/or n (H 2 )

(b) (i) Use of graph paper linear numerical scale chosen for x axis AND Time / s added as label AND ALL points plotted correctly 

1 AO2.

×

ALLOW Time (s) OR Time in s ALLOW seconds OR sec OR secs

Tolerance ± 1 small square

Point at 0,0 NOT required ALLOW up to 3 plotting errors

(ii) Anomaly point at 80 s circled 

1 AO2.

×

ALLOW one more anomalous point NOT on the curve drawn in (iii)

(iii) Line smooth curve using all points EXCEPT point at 80 s 

1 AO3.

(c) Initial slope is steeper AND curve levels off at an earlier time 

Same volume of gas produced (58 cm^3 ) 

2 AO2.

× 2

Tolerance ± 1 small square

H032/02 Mark Scheme June 2019

Question Answer Marks AO element

Guidance

5 (a) (i) Product with H 2 H H H H H H

3 AO1.

× 3

ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous

H C C C C C C H ALLOW^ part molecular formulae but not full

H H H H H H 

Product with HCl

H H H H H H

H C C C C C C H

H H H H Cl H (^) 

Product with Br (^2)

H H H H H H

H C C C C C C H

H H H H Br Br (^) 

(ii) Nickel/Ni  1 AO1.2 ALLOW Pt OR Pd OR Rh

(iii) (orange to) colourless OR bromine is decolourised 

1 AO1.2 ALLOW ‘it decolourises / turns colourless’ IGNORE colour change

H032/02 Mark Scheme June 2019

Question Answer Marks AO element

Guidance

5 (b) (i) Please refer to the marking instructions on page 4 of this (^6) Indicative scientific points may include: Calcul ation from moles  n (hex-1-ene) = 4.20 = 0.0500 (mol)

 n (hexan-1-ol) needed = 0.0500 × 100 = 0.0800 (mol)

 mass needed = 0.0800 × 102 = 8.16 g  (^) OR volume 8.16 = 9.95 cm 3

CHECK for extent of errors by ECF. Calculation from mass  Theoretical mass hex-1-ene = 4.20 × 100 = 6.72 g

 Theoretical n (hex-1-ene) = 6.72 = 0.0800 (mol) 84  Mass of hexan-1-ol = 102 × 0.0800 = 8.16 g ALLOW small slip/rounding errors such as errors on M r (e.g. use of 83 instead of 84 for hex-1-ene M r )

Purification  Use of a separating funnel to separate organic and aqueous layers  Drying with an anhydrous salt  Distillation

Fine detail  Collection of upper layer (less dense from separating funnel)  Example of drying agent, e.g. MgSO 4 , CaC l 2  Collection of fraction distilling at 63ºC (boiling point of hex-1-ene) Incorrect purification method NOT creditworthy

Examples of partly correct calculations Mass = 5.1 g from 0.0500 × 102 % yield omitted Mass = 3.1875 g from 0.0500 × 62.5^ × 102 % yield inverted 100

mark scheme for guidance on how to mark this question. AO2. × Level 3 (5–6 marks) Calculates the correct mass of hexan-1-ol. AND Explains the purification steps, with most fine detail.

There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated.

AO3.

×

Level 2 (3–4 marks) Attempts a calculation of the mass of hexan- 1 - ol which is partly correct. OR Outlines the purification steps, with some fine detail.

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) Attempts the calculation but makes little progress. OR Briefly outlines the purification steps, which may be incomplete.

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.

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