How many SCSA Chemistry questions cover Science Inquiry Skills?

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SCSA Chemistry Science Inquiry Skills

5 sample questions with marking guides and sample answers · Avg. score: 25%

2024

SCSA

1 mark

Which statement best outlines the difference between systematic and random errors?
Systematic errors

will consistently produce measured values either above or below the actual value, while random errors will produce measured values above and below the actual value.

can be reduced through multiple trials and averaging of results, while random errors cannot be reduced.

are generally accurate but not precise, while random errors are generally precise but may not be accurate.

are difficult to avoid, while random errors can be readily improved.

Q17

2021

SCSA

1 mark

Q17

1 mark

A chemist performed a series of titrations and published the results in a scientific journal. From the point of view of the chemist, the titration data is

primary.

secondary.

personal.

investigative.

Q39

2022

SCSA

16 marks

Q39

A student wanted to investigate how changing temperature would influence how rapidly oxalic acid solution would decolourise an acidified potassium permanganate solution.

The student was provided with the following chemicals and equipment:

0.1 mol L $^{-1}$ acidified potassium permanganate solution
0.1 mol L $^{-1}$ oxalic acid solution
250 mL conical flasks
Bunsen burner
tripod and gauze mat
thermometer
stop watches
5.00 mL, 10.00 mL, 20.00 mL and 25.00 mL pipettes
distilled water
25.0 mL measuring cylinders.

Q39a

2 marks

State a hypothesis for this investigation.

Answer could include:
Increasing the temperature will decrease the time taken for the acidified potassium permanganate to decolourise (change from purple to pale pink/colourless as the rate of reaction increases with increasing temperature).

Marking Criteria

Descriptor	Marks
Writes a hypothesis that gives the relationship between the independent and dependent variables.	2
Writes a hypothesis that includes the independent and dependent variables without giving their relationship.	1
None of the above	0

Q39b

2 marks

Identify the independent and dependent variables.

The independent variable is the temperature of the solution.

The dependent variable is the time taken for the potassium permanganate solution/mixture to decolourise.

Marking Criteria

Descriptor	Marks
Identifies the independent variable as temperature (of solution)	1
Identifies the dependent variable as time taken (for potassium permanganate solution/mixture) to decolourise	1

Q39c

2 marks

Identify two control variables.

Answers could include (any 2 of):

concentration of acidified potassium permanganate solution
concentration of oxalic acid solution
volume of acidified potassium permanganate solution
volume of oxalic acid solution
stopwatch/timer
person timing/observing.

Marking Criteria

Descriptor	Marks
1 mark for each correct point (any 2 of): concentration of acidified potassium permanganate solution, concentration of oxalic acid solution, volume of acidified potassium permanganate solution, volume of oxalic acid solution, stopwatch/timer, person timing/observing.	2

Q39d

6 marks

Describe a procedure for this investigation.

A possible answer:

Fixed volumes of oxalic acid and acidified potassium permanganate are used. Temperature must be varied and measured, and time must be measured from mixing. Repeated trials should be conducted.

Additionally, an appropriate method for determining the end point of the reaction (decolourisation) is used, e.g. a white paper base.

Marking Criteria

Descriptor	Marks
Recognises that fixed volumes of both oxalic acid and acidified potassium permanganate are used (1 mark for recognising fixed volume of only one)	2
Recognises that temperature must be varied and measured	1
Recognises that time must be measured from mixing	1
1 mark for each correct point (any 2 of): recognition of appropriate method for determining end point of the reaction (decolourisation) e.g. use a white paper base, recognition of the use of trials, recognition of the use of appropriate glassware, recognition that solutions are mixed in appropriate proportions e.g. 2:5 ratio of solutions	2

Q39e

4 marks

Outline the difference between systematic and random errors. Use an example of each from this investigation to support your answer.

An answer could be:

Systematic errors produce consistently high or consistently low measurements compared to the true value. Random errors produce measurements that can fluctuate around the true value.

An example of a systematic error is only heating one solution. An example of a random error is not using the same measuring equipment during the reaction.

Marking Criteria

Descriptor	Marks
Recognises that systematic errors produce consistently high or consistently low measurements compared to the true value	1
Recognises that random errors produce measurements that can be either high or low/fluctuate around the true value	1
Provides an example of a systematic error (e.g. only heating one solution, using an inappropriate proportion of reactants, errors in calibration with equipment, inappropriate rinsing of glassware)	1
Provides an example of a random error (e.g. parallax (reading of meniscus), judging the end point, use of stopwatch, reading thermometer, not using the same measuring equipment during the reaction, using measuring cylinder rather than pipette)	1

Q38

2023

SCSA

10 marks

Q38

Groundwater, in addition to dam water and desalinated seawater, is part of the water supply to Perth homes. Groundwater contains a wide variety of chemicals that can affect the quality of drinking water. One of the contaminants is iron, often found in the form of iron(II) hydrogencarbonate.

The iron can be removed by the addition of chlorine gas. Enough calcium hydrogencarbonate is added to maintain a slightly basic pH. The reaction can be represented by the following equation:

2\text{ Fe(HCO}_3)_2 + \text{Cl}_2 + \text{Ca(HCO}_3)_2 \rightarrow 2\text{ Fe(OH)}_3 + \text{CaCl}_2 + 6\text{ CO}_2

Q38a

8 marks

7.00 g of chlorine gas is bubbled through 30 000 L of groundwater containing 39 010 mg of iron(II) hydrogencarbonate to which 16.22 g of calcium hydrogencarbonate has been added. Calculate the mass of iron(III) hydroxide that will be precipitated.

$n(\mathrm{Cl_2}) = \frac{7.00}{70.9} = 0.0987\ \mathrm{mol}$

$n\!\left(\mathrm{Fe(HCO_3)_2}\right) = \frac{39010}{1000 \times 177.886} = 0.2193\ \mathrm{mol}$

$n\!\left(\mathrm{Ca(HCO_3)_2}\right) = \frac{16.22}{162.116} = 0.100\ \mathrm{mol}$

$\text{1 mole of }\mathrm{Cl_2}\text{ reacts with 2 moles of }\mathrm{Fe(HCO_3)_2}\text{ and 1 mole of }\mathrm{Ca(HCO_3)_2}$

$\text{0.0987 mol of }\mathrm{Cl_2}\text{ will react with 0.197 mol of }\mathrm{Fe(HCO_3)_2}\text{ and 0.0987 mol of }\mathrm{Ca(HCO_3)_2}$

$\text{Since }n\!\left(\mathrm{Fe(HCO_3)_2}\right)\text{ required is less than }n\!\left(\mathrm{Fe(HCO_3)_2}\right)\text{ available, and the }n\!\left(\mathrm{Ca(HCO_3)_2}\right)\text{ required is less than the }n\!\left(\mathrm{Ca(HCO_3)_2}\right)\text{ available,} \mathrm{Cl_2}\text{ is the limiting reagent.}$

$n\!\left(\mathrm{Fe(OH)_3}\right) = 2n(\mathrm{Cl_2}) = 0.197\ \mathrm{mol}$

$m\!\left(\mathrm{Fe(OH)_3}\right) = 0.197 \times 106.874 = 21.1\ \mathrm{g}$

Marking Criteria

Moles calculation

Descriptor	Marks
$n(\text{Cl}_2) = 7.00/70.9 = 0.0987 \text{ mol}$	1
$n(\text{Fe}(\text{HCO}_3)_2) = 39010/1000/177.886 = 0.2193 \text{ mol}$	1
$n(\text{Ca}(\text{HCO}_3)_2) = 16.22/162.116 = 0.100 \text{ mol}$	1

Limiting reagent determination

Marking Bands

Descriptor	Marks
Correctly determines $\text{Cl}_2$ is limiting reagent with full justification (e.g., comparing required vs available moles)	3
Determines $\text{Cl}_2$ is limiting reagent with partial justification	2
Attempts to determine limiting reagent	1
None of the above	0

Final calculation

Descriptor	Marks
$n(\text{Fe}(\text{OH})_3) = 2n(\text{Cl}_2) = 0.197 \text{ mol}$	1
$m(\text{Fe}(\text{OH})_3) = 0.197 \times 106.874 = 21.1 \text{ g}$	1

Q38b

2 marks

Calculate the concentration of calcium chloride in the final solution.

$n(\text{CaCl}_2) = n(\text{Cl}_2) = 0.0987 \text{ mole}$
$c(\text{CaCl}_2) = \frac{0.0987}{30000} = 3.29 \times 10^{-6} \text{ mol L}^{-1}$

Marking Criteria

Descriptor	Marks
$n(\text{CaCl}_2) = n(\text{Cl}_2) = 0.0987 \text{ mole}$	1
$c(\text{CaCl}_2) = 0.0987/30000 = 3.29 \times 10^{-6} \text{ mol L}^{-1}$	1

Q30

2023

SCSA

12 marks

Q30

Write a balanced ionic equation for any reactions occurring between the following substances and state any observations before and after mixing.

If there is no reaction, write 'no reaction' for the equation and if there is no change observed write 'no visible reaction'. Use the colours stated in the Data booklet if required.

Q30a

4 marks

A piece of iron wool is added to a $0.1\text{ mol L}^{-1}$ solution of copper(II) sulfate.

Equation:
$\text{Fe(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Cu(s)} + \text{Fe}^{2+}\text{(aq)}$

Observed colour change/s:

a grey/silver solid and blue solution
form a salmon pink solid (solution decolourises/pale green)

Marking Criteria

Equation

Descriptor	Marks
Correct reactants	1
Correct products	1

Observed colour change/s

Descriptor	Marks
a grey/silver solid and blue solution	1
form a salmon pink solid (solution decolourises/pale green)	1

Q30b

4 marks

Calcium hydrogencarbonate powder is added to excess $1\text{ mol L}^{-1}$ nitric acid.

Equation
$\text{Ca(HCO}_3)_2\text{(s)} + 2 \text{H}^+\text{(aq)} \rightarrow \text{Ca}^{2+}\text{(aq)} + 2 \text{H}_2\text{O(l)} + 2 \text{CO}_2\text{(g)}$

Observed colour change/s:

white solid and colourless solution
solid dissolves/reacts and there is effervescence (bubbling)

Marking Criteria

Equation

Descriptor	Marks
Correct species	1
Correct balancing	1

Observed colour change/s

Descriptor	Marks
white solid and colourless solution	1
solid dissolves/reacts and there is effervescence (bubbling)	1

Q30c

4 marks

Excess chlorine gas is bubbled through a $0.1\text{ mol L}^{-1}$ sodium bromide solution.

Equation:
$2 \text{Br}^-\text{(aq)} + \text{Cl}_2\text{(g)} \rightarrow \text{Br}_2\text{(aq)} + 2 \text{Cl}^-\text{(aq)}$

Observed colour change/s:

greenish-yellow gas is bubbled through a colourless solution
forms an orange solution

Marking Criteria

Equation

Descriptor	Marks
Correct species	1
Correct balancing	1

Observed colour change/s

Descriptor	Marks
greenish-yellow gas is bubbled through a colourless solution	1
forms an orange solution	1

SCSA Chemistry Science Inquiry Skills

Moles calculation

Limiting reagent determination

Final calculation

Equation

Observed colour change/s

Equation

Observed colour change/s

Equation

Observed colour change/s

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