Level 2 Chemistry Internal Assessment Resource

Internal assessment resource Chemistry 2.2A v3 for Achievement Standard 91162

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Internal Assessment Resource

Chemistry Level 2

This resource supports assessment against:
Achievement Standard 91162 version 2
Carry out procedures to identify ions present in solution
Resource title: Which Ion?
3 credits
This resource:
· Clarifies the requirements of the standard
· Supports good assessment practice
· Should be subjected to the school’s usual assessment quality assurance process
· Should be modified to make the context relevant to students in their school environment and ensure that submitted evidence is authentic
Date version published by Ministry of Education / February 2017 Version 3
To support internal assessment from 2017
Quality assurance status / These materials have been quality assured by NZQA.
NZQA Approved number: A-A-02-2017-91162-03-5799
Authenticity of evidence / Teachers must manage authenticity for any assessment from a public source, because students may have access to the assessment schedule or student exemplar material.
Using this assessment resource without modification may mean that students’ work is not authentic. The teacher may need to change figures, measurements or data sources or set a different context or topic to be investigated or a different text to read or perform.

Internal assessment resource Chemistry 2.2A v3 for Achievement Standard 91162

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Internal Assessment Resource

Achievement Standard Chemistry 91162: Carry out procedures to identify ions present in solution

Resource reference: Chemistry 2.2A v3

Resource title: Which Ion?

Credits: 3

Teacher guidelines

The following guidelines are supplied to enable teachers to carry out valid and consistent assessment using this internal assessment resource.

Teachers need to be very familiar with the outcome being assessed by Achievement Standard Chemistry 91162. The achievement criteria and the explanatory notes contain information, definitions, and requirements that are crucial when interpreting the standard and assessing students against it.

Context/setting

This activity requires students to use given qualitative procedures to identify ions present in a number of solutions.

Conditions

This assessment activity is designed to take place over 1–2 periods of in-class time. Adjust these conditions to suit your students and context.

Resource requirements

· red litmus paper

· 1 mol L-1 HCl (aq)

· 0.1 mol L-1 AgNO3 (aq)

· 0.1 mol L-1 BaCl2 (aq)

· 1 mol L-1 NH3 (aq)

· 1 mol L-1 NaOH (aq)

· 0.1 mol L-1 KSCN (aq)

· 1 mol L-1 H2SO4 (aq)

· Unknown solutions:

o A: NaCl

o B: Na2SO4

o C: Na2CO3

o D: Cu(NO3)2

o E: Ba(NO3)2

o F: Pb(NO3)2

o G: Mg(NO3)2

· safety goggles, test tubes, test tube racks, test tube brushes, droppers.

Additional information

You should not use the activity exactly as it is (same ions in same order) since it is available to all students and the assessment schedule includes examples of appropriate responses. For example, you could substitute the ions given in this activity with other appropriate ions (see EN 5).

The teacher could substitute the flow chart given in the student resources for an alternative flow chart/procedure that would enable students to identify the ions in solutions.

You should carry out tests prior to the assessment to ensure that students will be able to identify the ions with the solutions provided.

Internal assessment resource Chemistry 2.2A v3 for Achievement Standard 91162

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Internal Assessment Resource

Achievement Standard Chemistry 91162: Carry out procedures to identify ions present in solution

Resource reference: Chemistry 2.2A v3

Resource title: Which Ion?

Credits: 3

Achievement / Achievement with Merit / Achievement with Excellence
Carry out procedures to identify ions present in solution. / Carry out procedures to justify the identification of ions present in solution. / Carry out procedures to comprehensively justify the identification of ions present in solution.

Student instructions

Introduction

This assessment activity requires you to use given qualitative procedures to identify ions present in a number of solutions. You will then write a report to support the identification of the ions in the solutions.

You will be assessed on how well you carry out these given procedures to identify the ions in the solutions.

Your teacher will guide you about how much time you will have for this activity.

This is an individual activity.

Task: Identifying Ions in Solutions

Use the aqueous solutions and the procedures in the flow charts provided in Student Resources A and B to identify the anions present in unknown solutions A – C and the cations present in unknown solutions D – G.

Complete all the necessary procedures for solutions A – G, identify as many ions as possible and write equations to support your identification.

Method

· Carry out procedures to identify the ion in each unknown solution using the aqueous solutions and the flow charts provided in Student Resources A and B.

· Record the steps you used to identify the ions and any observations you made during the procedures. Use this primary data to identify the ions in the solutions.

· For each ion identified:

– name the ion present in the solution

– describe the steps you used to identify the ion

– describe the observations you made during each step of the procedure

– identify by name or formula all precipitates formed

– write balanced equations for all the reactions where precipitates are formed

– write balanced equations for all the reactions where complex ions are formed

– link your observations to any equations you write for the formation of precipitates and/or complex ions.

Internal assessment resource Chemistry 2.2A v3 for Achievement Standard 91162

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Student Resource A:

Testing for anions flow charts: Cl-, CO32-, I-, NO3-, OH-, SO42-

Student Resource B:

Testing for cations flow chart: Ag+, Al3+, Ba2+, Cu2+, Fe2+, Fe3+, Mg2+, Pb2+, Na+, Zn2+

Internal assessment resource Chemistry 2.2A v3 for Achievement Standard 91162

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Assessment schedule: Chemistry 91162 Which Ion?

Evidence/Judgements for Achievement / Evidence/Judgements for Achievement with Merit / Evidence/Judgements for Achievement with Excellence
The student identifies ions which form precipitates correctly.
The student supports their identification of ions with experimental observations.
For each of the ions, the student identifies by name or formula all precipitates formed and supports their responses with the evidence required.
For example:
Solution F is Pb2+
When 2 drops of NaOH are added a white precipitate forms. The precipitate is lead hydroxide / Pb(OH)2(s)
When excess NaOH is added the precipitate dissolves.
When 2 drops of NH3 are added to a new sample a white precipitate forms. The precipitate is lead hydroxide / Pb(OH)2(s).
When excess aqueous NH3 is added the precipitate remains.
When H2SO4 is added to a new sample a white precipitate forms. The precipitate is lead sulphate / PbSO4(s). / The student identifies ions which form precipitates correctly.
The student supports their identification of ions with experimental observations.
For each of the ions, the student identifies by name or formula all precipitates formed, justifies their identification of the ions, writes balanced equations for all of the reactions where precipitates are formed, and links all precipitation equations to the observations made during the procedure.
The student supports their responses with the evidence required.
For example:
Solution F is Pb2+
When 2 drops of NaOH are added a white precipitate forms. The precipitate is lead hydroxide / Pb(OH)2(s):
Pb2+(aq) + 2 OH-(aq) ® Pb(OH)2(s).
When excess NaOH is added the precipitate dissolves.
When 2 drops of NH3 are added to a new sample a white precipitate forms. The precipitate is lead hydroxide / Pb(OH)2(s):
Pb2+(aq) + 2 OH-(aq) ® Pb(OH)2(s)
When excess aqueous NH3 is added the precipitate remains.
When H2SO4 is added to a new sample a white precipitate forms. The precipitate is lead sulphate / PbSO4(s):
Pb2+(aq) + SO42-(aq) ® PbSO4(s). / The student identifies ions which form precipitates and complex ions correctly.
The student supports their identification of ions with experimental observations.
For each of the ions, the student identifies by name or formula all precipitates formed, comprehensively justifies their identification of the ions, writes balanced equations for all of the reactions where precipitates and complex ions are formed, and links all precipitation and complex ion equations to the observations made during the procedure.
The student supports their responses with the evidence required.
For example:
Solution F is Pb2+
When 2 drops of NaOH are added a white precipitate forms. The precipitate is lead hydroxide / Pb(OH)2(s):
Pb2+(aq) + 2 OH-(aq) ® Pb(OH)2(s)
When excess NaOH is added the precipitate dissolves:
Pb(OH)2(s) + 2 OH-(aq) ® [Pb(OH)4]2-(aq)
or
Pb2+(aq) + 4 OH-(aq) ® [Pb(OH)4]2-(aq)
This means it could be Al3+, Zn2+or Pb2+
When 2 drops of NH3 are added to a new sample a white precipitate forms. The precipitate is lead hydroxide / Pb(OH)2(s):
Pb2+(aq) + 2 OH-(aq) ® Pb(OH)2(s)
When excess aqueous NH3 is added the precipitate remains which means it is either Al3+ or Pb2+.
When H2SO4 is added to a new sample a white precipitate forms this means it can only be Pb2+. The precipitate is lead sulphate / PbSO4(s):
Pb2+(aq) + SO42-(aq) ® PbSO4(s)

Final grades will be decided using professional judgement based on a holistic examination of the evidence provided against the criteria in the Achievement Standard.