Chemistry marking guide and solution - Queensland Curriculum and ...

Chemistry marking guide and

solution

Sample external assessment 2020

Science (125 marks)

Assessment objectives

This assessment instrument is used to determine student achievement in the following

objectives:

1. describe and explain chemical equilibrium systems, oxidation and reduction, properties and

structure of organic materials, and chemical synthesis and design

2. apply understanding of chemical equilibrium systems, oxidation and reduction, properties

and structure of organic materials, and chemical synthesis and design

3. analysis evidence about chemical equilibrium systems, oxidation and reduction, properties

and structure of organic materials, and chemical synthesis and design to identify trends,

patterns, relationships, limitations or uncertainty

4. interpret evidence about chemical equilibrium systems, oxidation and reduction, properties

and structure of organic materials, and chemical synthesis and design to draw conclusions

based on analysis.

Introduction

The Queensland Curriculum and Assessment Authority (QCAA) has developed mock external

assessments for each General senior syllabus subject to support the introduction of external

assessment in Queensland.

An external assessment marking guide (EAMG) has been created specifically for each mock

external assessment.

The mock external assessments and their marking guides were:

? developed in close consultation with subject matter experts drawn from schools, subject

associations and universities

? aligned to the external assessment conditions and specifications in General senior syllabuses

? developed under secure conditions.

Purpose

This document consists of an EAMG and an annotated response.

The EAMG:

? provides a tool for calibrating external assessment markers to ensure reliability of results

? indicates the correlation, for each question, between mark allocation and qualities at each

level of the mark range

? informs schools and students about how marks are matched to qualities in student responses.

Mark allocation

Where a response does not meet any of the descriptors for a question or a criterion, a mark of ¡®0¡¯

will be recorded.

Where no response to a question has been made, a mark of ¡®N¡¯ will be recorded.

Marking guide and solution

Sample external assessment 2020

Queensland Curriculum & Assessment Authority

External assessment marking guide

Paper 1 ¡ª Section 1: Multiple choice

Question

Response

1

C

2

D

3

B

4

A

5

B

6

A

7

B

8

D

9

C

10

C

11

D

12

A

13

C

14

D

15

B

16

A

17

D

18

D

19

C

20

D

21

B

22

D

23

C

24

A

25

D

Chemistry marking guide and solution

Sample external assessment 2020

Queensland Curriculum & Assessment Authority

Paper 1 ¡ª Section 2: Short response

Question

Sample response

The response

26

a)

D

? determines structure with

tertiary carbon is D [1 mark]

b)

propan-2-ol

? determines name is

propan-2-ol [1 mark]

Ethane is insoluble in water because it contains only a non-polar

hydrocarbon chain. The inter-molecular forces are dispersion forces

only.

? identifies that ethane is

insoluble due to dispersion

forces [1 mark]

Ethanol and ethanoic acid are both soluble in water as the hydroxyl (ROH) and carboxyl (R-COOH) groups forms H-bonds with water

molecules

? identifies that ethanol is

soluble due to H-bonds

between the hydroxyl group

and water [1 mark]

The non-polar hydrocarbon chains in ethanol and ethanoic acid are

small and have weak dispersion forces which do not interfere with the

H-bonding and their solubility in water.

? identifies that ethanoic acid is

soluble due to H-bonding

between the carboxyl group

and water [1 mark]

27

Chemistry marking guide and solution

Sample external assessment 2020

Queensland Curriculum & Assessment Authority

Question

Sample response

28

29

The response

? correctly identifies

equivalence point > 7

[1 mark]

? correctly identifies buffer

region [1 mark]

? identifies initial pH 3 [1 mark]

a)

b)

Stage 2

? identifies stage 2 [1 mark]

Because it¡¯s a reversible reaction where all the products and reactants

are gases.

? indicates stage 2 is affected

by pressure because it is

reversible, and all of the

reactants and products are

gases [1 mark]

??H2 SO4 required = 1 100 000/98.08 = 11 215 mol

? correctly determines

??H2 SO4 = 11 215 [1 mark]

??SO3 required = 11 215/0.97 = 11 562 mol

??SO3 : ??S = 1:1 = 11 562 mol

mass S = 11 562 ¡Á 32.06 = 370 678 g

Mass = 371 kg

Chemistry marking guide and solution

Sample external assessment 2020

? determines ??SO3 = 11 562

[1 mark]

? determines ??SO3 : ??S = 11 562

[1 mark]

? determines mass S = 371

[1 mark]

Queensland Curriculum & Assessment Authority

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