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 -- 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 -- Section 2: Short response

Question Sample response 26 a) D

b) propan-2-ol

The response

? determines structure with tertiary carbon is D [1 mark]

? determines name is propan-2-ol [1 mark]

27

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

? identifies that ethane is

hydrocarbon chain. The inter-molecular forces are dispersion forces

insoluble due to dispersion

only.

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]

Chemistry marking guide and solution Sample external assessment 2020

Queensland Curriculum & Assessment Authority

Question Sample response 28

The response

? correctly identifies equivalence point > 7 [1 mark]

? correctly identifies buffer region [1 mark]

? identifies initial pH 3 [1 mark]

29 a) 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]

b) H2SO4 required = 1 100 000/98.08 = 11 215 mol

? correctly determines H2SO4 = 11 215 [1 mark]

SO3 required = 11 215/0.97 = 11 562 mol

SO3: S = 1:1 = 11 562 mol

mass S = 11 562 ? 32.06 = 370 678 g Mass = 371 kg

? determines SO3 = 11 562 [1 mark]

? determines SO3: S = 11 562 [1 mark]

? determines mass S = 371 [1 mark]

Chemistry marking guide and solution Sample external assessment 2020

Queensland Curriculum & Assessment Authority

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