Chemistry SBA

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Chemistry SBA
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BAC (Qualitative analysis) Version 1

• Link with NSS curriculum
• Topic IV (Acids and Bases)
• Number of period required
• 1 ? 40 minutes
• Experimental work 20 minutes
• Prior knowledge
• sub-sections (a) and (d) of topic IV
• Objective
• To test the students knowledge on precipitation
  reactions and acid-carbonate reactions
• Assessment
• Mainly based on the written worksheet

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BAC (Qualitative analysis) Version 1

• Instructions
• Given MgSO4(aq) Na2CO3(aq) Pb(NO3)2 and
  HCl(aq)
• Perform the tests as in table below.
• Observations?
• Identification?

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BAC (Qualitative analysis) Version 1
Mixing solutions Observation
A( ) B( )
A ( ) C( )
A( ) D( )
B( ) C( )
B( ) D( )
C( ) D( )
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Assessment considerations

• Mainly based on written worksheets
• Any unsafe practice?
• Marks to be deducted
• With prior notice

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Marking criteria
Mark Remarks
10 - 9 Accurate description of nearly all results. Logical deduction of the unknown. Safety procedures have been observed.
8 6 Accurate description of some results. Can deduce the cation / anion logically. Safety procedures have been observed.
5 3 Accurate description of at least one result. Can state the cation / anion.
2 1 Accurate description of one result OR Can state the cation / anion.
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BAC (Qualitative analysis) Version 1 EXEMPLAR
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BAC (Qualitative analysis) Version 1 EXEMPLAR
In this exemplar, the student correctly
identified the four substances. However, in
recording his observations, he wrongly stated no
observable change as no observations. Moreover,
the description on his deduction is not
systematic and could not convey his ideas clearly.
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BAC (Qualitative analysis) Version 2

• Link with NSS curriculum
• Topic IV (Acids and Bases) Topic VII (Redox
  reactions)
• Number of periods required
• 1 ? 40 minutes
• The students are able to complete the experiment
  and hand in the worksheet within 30 minutes.

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BAC (Qualitative analysis) Version 2
1 Describe the sample.
2 Estimate, using universal test paper, the pH of an aqueous solution of the sample.
3 Report on the action of HCl on an aqueous solution of the sample.
4 Report on the action of H2SO4 on an aqueous solution of the sample.
5 Report on the action of NaOH on an aqueous solution of the sample.
6 Report on the action of aqueous NH3 on an aqueous solution of the sample.
7 Report on the action of a few drops of KMnO4 in H2SO4 on an aqueous solution of the sample.
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BAC (Qualitative analysis) Version 2

• Note 2/3 of the marks are allocated to the
  observations. 1/3 of the marks are allocated to
  the interpretation of the observations and the
  deduction of the chemical nature of the sample.
• Summarise, in the space below, your conclusions
  as to the chemical nature of the sample. Deduce,
  where possible, what ionic and / or molecular
  species are present in the sample.

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BAC (Qualitative analysis) Version 2 EXEMPLAR
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BAC (Qualitative analysis) Version 2 EXEMPLAR
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Points to take note

• Safety practice
• Safety goggles
• Safety first before assessment
• Adequate number of apparatus / chemical reagents
• Use reagent bottles with dropper
• Flame test
• 2 fume cupboards FE
• Test tube vs. microscale