NESA Chemistry Questioning and Predicting
3 sample questions with marking guides and sample answers · Avg. score: 97.7%
Scientific posters communicate the findings of scientific investigations.
Which section of a scientific poster should explain the reason for undertaking an investigation?
discussion
conclusion
introduction
methodology
Reveal Answer
discussion
The discussion section is used to interpret the results, explain their significance, and compare them to existing literature, not to state the initial reason for the study.
conclusion
The conclusion summarizes the main findings of the investigation and their broader implications, rather than explaining why the study was started.
introduction
The introduction provides the background information, context, and the specific rationale or reason for undertaking the investigation.
methodology
The methodology section details the procedures, materials, and techniques used to conduct the investigation, not the reason for doing it.
Refer to the following equation for the dissolution of gaseous carbon dioxide into the oceans.
Which of the following statements forms an hypothesis that is consistent with this equation?
The level of carbon dioxide in the atmosphere is increasing over time.
An increase in the concentration of carbon dioxide dissolved in the oceans results in an increase in the surface temperatures of the oceans.
Carbon dioxide in the atmosphere is being consumed as it dissolves in the ocean, resulting in increasing ocean acidity.
Ocean acidification, caused by the increased concentration of carbonic acid, shifts the equilibrium of carbonate chemistry in seawater, reducing the rate and extent of calcification in marine organisms.
Reveal Answer
The level of carbon dioxide in the atmosphere is increasing over time.
This statement describes a temporal trend of a single variable (CO2 over time), whereas the equation likely establishes a functional relationship between two distinct physical variables (CO2 and temperature).
An increase in the concentration of carbon dioxide dissolved in the oceans results in an increase in the surface temperatures of the oceans.
This hypothesis is consistent with the equation, which likely models a positive correlation where an increase in the independent variable (dissolved ) is associated with an increase in the dependent variable (ocean surface temperature).
Carbon dioxide in the atmosphere is being consumed as it dissolves in the ocean, resulting in increasing ocean acidity.
While this describes the chemical process of ocean acidification, it focuses on the relationship between and acidity (), rather than the relationship between and temperature implied by the correct answer.
Ocean acidification, caused by the increased concentration of carbonic acid, shifts the equilibrium of carbonate chemistry in seawater, reducing the rate and extent of calcification in marine organisms.
This hypothesis focuses on biological impacts (calcification rates) and carbonate equilibrium, which involves different variables and mechanisms than the specific temperature-concentration relationship described by the equation.
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 acidified potassium permanganate solution
- 0.1 mol L 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.
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).
| 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 |
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.
| 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 |
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.
| 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 |
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.
| 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 |
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.
| 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 |