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NESA Chemistry Analysing Data and Information

14 sample questions with marking guides and sample answers · Avg. score: 73.5%

Q26

2024

VCAA

1 mark

Q26

1 mark

Use the following information to answer the question.

A chemist runs a mixture of hexane, hexan-1-ol and hexan-2-one through a high-performance liquid chromatography (HPLC) column using a polar mobile phase and a non-polar stationary phase.

The chemist wants to determine the concentration of hexane in the mixture.

Which one of the following will provide information to allow the hexane concentration to be accurately calculated?

running a series of known concentrations of hexane through the HPLC column under the same conditions

running the HPLC experiment using a non-polar mobile phase and a polar stationary phase

using published retention times and peak sizes of standard hexane chromatographs

reducing the HPLC column temperature to achieve better separation of the compounds

Reveal Answer

running a series of known concentrations of hexane through the HPLC column under the same conditions

Correct Answer

To accurately determine concentration, a calibration curve must be constructed by running standard solutions of known concentrations under the exact same experimental conditions to compare peak areas.

running the HPLC experiment using a non-polar mobile phase and a polar stationary phase

Changing the polarity of the mobile and stationary phases alters the separation method (switching to normal phase chromatography) but does not provide the quantitative reference data needed to calculate concentration.

using published retention times and peak sizes of standard hexane chromatographs

Retention times and peak sizes are highly dependent on the specific instrument, column age, and exact experimental conditions, so published data cannot be reliably used for quantitative analysis.

reducing the HPLC column temperature to achieve better separation of the compounds

While reducing the temperature might improve the separation (resolution) of the peaks, it does not provide the reference standards required to calculate the actual concentration of the compound.

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.

Reveal Answer

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.

Correct Answer

Systematic errors shift measurements in one consistent direction (either always too high or always too low), whereas random errors cause unpredictable fluctuations both above and below the true value.

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

This statement has it backwards. Random errors can be reduced by taking multiple trials and averaging the results, but systematic errors will persist regardless of how many trials are averaged.

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

This is the opposite of the truth. Systematic errors reduce accuracy by shifting the mean away from the true value, while random errors reduce precision by scattering the data points.

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

Systematic errors can often be identified and eliminated through proper equipment calibration, whereas random errors are inherent to the measurement process and cannot be completely avoided.

2020

VCAA

1 mark

Using large sample sizes in an experiment increases

reliability.

precision.

validity.

uncertainty.

Reveal Answer

reliability.

Correct Answer

Reliability refers to the consistency and repeatability of experimental results. Using a larger sample size reduces the impact of random errors and outliers, making the findings more reliable.

precision.

In experimental design, precision typically refers to the exactness or resolution of the measuring instrument. Increasing the sample size does not improve the precision of the tools being used.

validity.

Validity refers to how accurately an experiment measures what it is intended to measure. A large sample size cannot fix underlying flaws, confounding variables, or biases in the experimental design.

uncertainty.

Using a larger sample size actually decreases uncertainty. More data points reduce the margin of error, providing a more confident estimate of the true population parameter.

2022

SCSA

1 mark

Consider an acid-base titration between hydrochloric acid solution and ammonia solution. Which of the following actions is least likely to cause an error when calculating the concentration of hydrochloric acid?

cleaning the pipette with distilled water before each titration

rinsing the sides of the conical flask with distilled water during the titration

measuring the ammonia solution in a 20 mL measuring cylinder

leaving the funnel in the burette for each titration

Reveal Answer

cleaning the pipette with distilled water before each titration

Rinsing the pipette with distilled water dilutes the solution being transferred, which alters the number of moles delivered and causes a calculation error.

rinsing the sides of the conical flask with distilled water during the titration

Correct Answer

Adding distilled water to the conical flask does not change the total number of moles of acid or base present, so it will not affect the titration results or the calculated concentration.

measuring the ammonia solution in a 20 mL measuring cylinder

A measuring cylinder is not precise enough for analytical titrations; a volumetric pipette must be used to avoid significant volume measurement errors.

leaving the funnel in the burette for each titration

Leaving the funnel in the burette can allow additional drops of solution to fall into the burette during the titration, leading to inaccurate volume readings.

Q23

2025

NESA

3 marks

Q23

3 marks

A student attempted to determine the % w/w of sulfate in a sample of solid fertiliser. They used the procedure described below.

Weigh a clean, dry beaker.
Add fertiliser to the beaker and weigh again.
Add 250 mL of distilled water and stir thoroughly.
Add 20 mL of 0.1 mol L $^{-1}$ BaCl $_2$ solution.
Filter out the BaSO $_4$ precipitate, using distilled water to ensure all of the solid is transferred from the beaker to the filter paper.
Put the filter paper and precipitate onto a weighed watch glass and leave them to dry for 20 minutes in the sun.
Weigh the watch glass, the filter paper and the precipitate.
Calculate the % w/w.

Justify TWO changes that can be made to the procedure to ensure more accurate results.

Reveal Answer

Filter out any insoluble components before step 4, or else these will contribute to the mass of the precipitate.

Weigh the filter paper, or else the mass of the precipitate will be inaccurate.

Marking Criteria

Descriptor	Marks
Justifies TWO appropriate changes with justifications of both related to accuracy	3
Justifies ONE appropriate change OR Identifies TWO appropriate changes	2
Provides some relevant information	1
None of the above	0

2024

SCSA

1 mark

Use the following information to answer the question.

A group of students conducted a series of titrations to determine the concentration of acetic acid in vinegar using the following steps:

i. A sample of vinegar was pipetted into a volumetric flask that had been rinsed with the vinegar and then deionised water added up to the mark.
ii. The volumetric flask was stoppered, and the diluted solution mixed thoroughly.
iii. Aliquots of the diluted vinegar solution were pipetted into conical flasks that had been rinsed with deionised water and a few drops of indicator added to each flask.
iv. A standardised sodium hydroxide solution was added to a burette that had been rinsed with deionised water.
v. Two samples of diluted vinegar were titrated against the sodium hydroxide solution and both values were used to calculate the concentration of the vinegar.

Which of the following does not explain why Step v contributed to the errors in the titration?

There were insufficient titrations

hence the sample size was too small.

to determine if either was an outlier.

to reduce random errors by averaging.

to identify the colour change.

Reveal Answer

hence the sample size was too small.

This is a valid explanation for the error. Two titrations represent a very small sample size, which decreases the reliability of the calculated concentration.

to determine if either was an outlier.

This is a valid explanation for the error. With only two titration values, it is impossible to identify if one of the results is an anomaly or outlier; typically, at least three concordant results are required.

to reduce random errors by averaging.

This is a valid explanation for the error. Performing multiple titrations and averaging the concordant results helps to minimize the impact of random errors, which cannot be effectively achieved with just two trials.

to identify the colour change.

Correct Answer

This does not explain the error. The ability to identify the colour change at the endpoint depends on the choice of indicator and the observer's perception, not on the number of titrations performed.

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.

Reveal Answer

primary.

Correct Answer

Primary data is data collected directly by the researcher for their own specific purpose. Since the chemist performed the titrations themselves, the data is primary.

secondary.

Secondary data is data collected by someone else. If another scientist used this published data, it would be secondary data to them, but not to the original chemist.

personal.

Personal data refers to information relating to an identified or identifiable individual, such as names or addresses, not experimental scientific results.

investigative.

While the chemist is conducting an investigation, "investigative" is not a standard statistical classification for the source of data.

2021

VCAA

1 mark

A titration was performed to determine the concentration of an ethanoic acid, $\text{C}_2\text{H}_4\text{O}_2$ , solution using the following procedure:

25.00 mL of the $\text{C}_2\text{H}_4\text{O}_2$ solution was pipetted into a conical flask.
A few drops of indicator were added to the flask.
A burette was filled with standard sodium hydroxide, NaOH, solution.
The $\text{C}_2\text{H}_4\text{O}_2$ solution was then titrated with the NaOH solution.
Steps 1–4 were repeated until three concordant titres were obtained.

A systematic error could result if the

burette tap leaked during one of the titrations.

burette readings were recorded to the nearest 0.1 mL.

number of drops of indicator was not consistent for each titration.

actual concentration of the standard NaOH solution was lower than the stated concentration.

Reveal Answer

burette tap leaked during one of the titrations.

A leak during only one titration is a mistake or random error, as it does not consistently affect all trials in the same way.

burette readings were recorded to the nearest 0.1 mL.

Recording readings to the nearest 0.1 mL affects the precision of the measurements, which contributes to random error rather than a consistent systematic error.

number of drops of indicator was not consistent for each titration.

An inconsistent number of drops introduces random error, as the variation changes unpredictably between each individual trial.

actual concentration of the standard NaOH solution was lower than the stated concentration.

Correct Answer

If the standard solution's concentration is lower than stated, a larger volume will be required for every titration, consistently skewing the calculated concentration of ethanoic acid higher. This consistent directional shift is the definition of a systematic error.

2022

VCAA

1 mark

Scientists often repeat trials of an experiment using the same experimental method and the same equipment.

Which one attribute of experimental data will be improved when there is an increase in the number of times that a trial is repeated?

bias

validity

accuracy

reliability

Reveal Answer

bias

Bias is a systematic error that consistently skews results in one direction. Repeating trials with the same method and equipment will simply reproduce the bias, not improve it.

validity

Validity refers to how well an experiment measures what it actually intends to measure. Repeating the exact same procedure does not change or improve its validity.

accuracy

Accuracy is how close a measurement is to the true or accepted value. If the equipment is miscalibrated, repeating trials will not make the average result any closer to the true value.

reliability

Correct Answer

Reliability refers to the consistency of experimental results. Increasing the number of trials reduces the impact of random errors and outliers, thereby improving the reliability of the data.

Q18

2021

SCSA

1 mark

Q18

1 mark

An example of a random error in a titration is

reading solution volumes to the bottom of the meniscus.

a gas bubble in the burette tap that comes out during a titration.

calculating the concentration of the primary standard incorrectly.

rinsing down the sides of the conical flasks during titrations.

Reveal Answer

reading solution volumes to the bottom of the meniscus.

Reading the volume to the bottom of the meniscus is the correct standard procedure for measuring liquids, not an error.

a gas bubble in the burette tap that comes out during a titration.

Correct Answer

A gas bubble escaping during a titration causes an unpredictable change in the volume reading for that specific trial, which is the definition of a random error.

calculating the concentration of the primary standard incorrectly.

An incorrect calculation of the primary standard's concentration is a systematic error (or blunder) that will consistently skew all subsequent results in the same direction.

rinsing down the sides of the conical flasks during titrations.

Rinsing the sides of the conical flask with deionized water is a correct technique to ensure all reactants are in the main solution, not an error.

2024

SCSA

1 mark

Use the following information to answer the question.

A group of students conducted a series of titrations to determine the concentration of acetic acid in vinegar using the following steps:

The students found it difficult to obtain consistent results from their titrations. Which of the steps could have been responsible for the difficulties?

iv and v only

i, ii, iv and v only

i, iv and v only

iii, iv and v only

Reveal Answer

iv and v only

While steps iv and v do cause inconsistencies, this option misses step i. Rinsing the volumetric flask with vinegar adds unmeasured moles of acid, which is a significant source of error.

i, ii, iv and v only

Step ii is a standard and correct procedure for preparing a diluted solution. Mixing the solution thoroughly ensures homogeneity and would not cause inconsistent results.

i, iv and v only

Correct Answer

Step i is incorrect because the volumetric flask should only be rinsed with deionised water. Step iv is incorrect because the burette must be rinsed with the titrant (NaOH) to prevent dilution. Step v is incorrect because titrations should be repeated until at least three concordant results are obtained.

iii, iv and v only

Step iii is a correct procedure. Conical flasks should be rinsed with deionised water, as rinsing them with the analyte would add extra, unmeasured moles of the substance being titrated.

Q24

2020

VCAA

1 mark

Q24

1 mark

Use the following information to answer the question.

A solution of citric acid, $\text{C}_3\text{H}_5\text{O(COOH)}_3$ , was analysed by titration.
25.0 mL aliquots of the $\text{C}_3\text{H}_5\text{O(COOH)}_3$ solution were titrated against a standardised solution of 0.0250 M sodium hydroxide, NaOH. Phenolphthalein indicator was used and the average titre was found to be 24.0 mL.

Which one of the following would have resulted in a concentration that is higher than the actual concentration?

The pipette was rinsed with NaOH solution.

The pipette was rinsed with $\text{C}_3\text{H}_5\text{O(COOH)}_3$ solution.

The conical flask was rinsed with NaOH solution.

The conical flask was rinsed with $\text{C}_3\text{H}_5\text{O(COOH)}_3$ solution.

Reveal Answer

The pipette was rinsed with NaOH solution.

Rinsing the pipette with NaOH would neutralize some of the citric acid before it is transferred to the flask. This decreases the required NaOH titre, resulting in a lower calculated concentration.

The pipette was rinsed with $\text{C}_3\text{H}_5\text{O(COOH)}_3$ solution.

Rinsing the pipette with the solution it will transfer (citric acid) is the standard correct procedure and ensures the concentration remains accurate.

The conical flask was rinsed with NaOH solution.

Rinsing the conical flask with NaOH adds extra base to the flask, which neutralizes some of the citric acid before titration begins. This decreases the required NaOH titre, leading to a lower calculated concentration.

The conical flask was rinsed with $\text{C}_3\text{H}_5\text{O(COOH)}_3$ solution.

Correct Answer

Rinsing the conical flask with citric acid leaves residual acid in the flask, meaning there is more acid present than just the 25.0 mL aliquot. This requires a larger volume of NaOH to neutralize, leading to a higher calculated concentration.

2021

VCAA

9 marks

Digesters use bacteria to convert organic waste into biogas, which contains mainly methane, $\text{CH}_4$ . Biogas can be used as a source of energy.

Q1b

A digester processed 1 kg of organic waste to produce 496.0 L of biogas at standard laboratory conditions (SLC). The biogas contained 60.0% $\text{CH}_4$ .

Q1c

Biogas was combusted to release $1.63 \times 10^3 \text{ kJ}$ of energy. This energy was used to heat 100 kg of water in a tank. The initial temperature of the water was 25.0 °C.

Q1a

1 mark

Both biogas and coal seam gas contain $\text{CH}_4$ as their main component.

Why is biogas considered a renewable energy source but coal seam gas is not?

Reveal Answer

Biogas is considered renewable because its production-and-use cycle is continuous so that it is constantly replenished whereas coal seam gas is used at a faster rate than it can be replenished.*

Marking Criteria

Descriptor	Marks
Provides a direct comparison of both biogas and coal seam gas indicating the period of time used to produce these materials	1

Q1b (i)

2 marks

Write the thermochemical equation for the complete combustion of $\text{CH}_4$ at SLC.

Reveal Answer

$CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)$ * $\Delta H = -890\ \mathrm{kJ\ mol^{-1}}$

Marking Criteria

Descriptor	Marks
Writes a correctly balanced chemical equation with associated states	1
Provides a molar enthalpy of combustion with a negative sign that matches the equation written	1

Q1b (ii)

3 marks

Calculate the amount of energy that could be produced by $\text{CH}_4$ from 1 kg of organic waste.

Reveal Answer

$n(\text{biogas}) = 496.0 / 24.8$

$= 20.0\ \mathrm{mol}$ *

$n(CH_4) = 0.60 \times 20.0$

$= 12.0\ \mathrm{mol}$ *

Energy $= 12.0\ \mathrm{mol} \times 890\ \mathrm{kJ\ mol^{-1}}$

$= 1.07 \times 10^4\ \mathrm{kJ}\ (10680\ \mathrm{kJ})\ \text{or}\ (10.7\ \mathrm{MJ})$ *

Marking Criteria

Descriptor	Marks
Calculates $n(\text{biogas})$ correctly	1
Calculates $n(\text{CH}_4)$ correctly	1
Calculates the energy produced correctly	1

Q1c (i)

2 marks

What is the maximum temperature that the water in the tank could reach?

Reveal Answer

Energy $= 4.18 \times m(H_2O) \times \Delta T$

$1.63 \times 10^3\ (\times 10^3) = 4.18 \times 100\ (\times 10^3) \times \Delta T$

$\Delta T = 1.63 \times 10^3 / (4.18 \times 100)$

$= 3.90\ ^\circ C$ *

$T_{\max} = 25.0 + 3.90$

$= 28.9\ ^\circ C\ (\text{or }302\ \mathrm{K})$ *

Marking Criteria

Descriptor	Marks
Calculates $\Delta T$ correctly	1
Calculates $T_{\max}$ correctly to three significant figures	1

Q1c (ii)

1 mark

State why this temperature may not be reached.

Reveal Answer

For example:

loss of heat/energy to the atmosphere
heat/energy loss in the combustion chamber
heat/energy loss since the tank material also is heated
heat/energy loss from the piping
faulty insulation

Marking Criteria

Descriptor	Marks
Provides any logical reason involving incomplete transfer of heat/energy to the water (e.g., loss of heat to the atmosphere, heat loss in the combustion chamber, heat loss to the tank material, heat loss from piping, or faulty insulation)	1

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.

Reveal Answer

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.

Reveal Answer

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.

Reveal Answer

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.

Reveal Answer

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.

Reveal 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

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