VCAA Chemistry How is scientific inquiry used to investigate the sustainable production of energy and/or materials?
6 sample questions with marking guides and sample answers
Using large sample sizes in an experiment increases
reliability.
precision.
validity.
uncertainty.
Reveal Answer
reliability.
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.
A titration was performed to determine the concentration of an ethanoic acid, , solution using the following procedure:
- 25.00 mL of the 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 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.
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.
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.
A student hypothesised that polishing the zinc, Zn, electrode in an Fe–Zn galvanic cell would increase the current produced by the cell.
What would be the most valid method of testing this hypothesis?
researching the scientific literature to determine how polishing changes the structure of Zn
measuring the conductivity of a Zn electrode after polishing it
measuring the change in mass per unit time of the Fe electrode in the same Fe–Zn galvanic cell before and after the Zn electrode was polished
measuring the current produced by two different Fe–Zn galvanic cells, one using a polished Zn electrode and the other using an unpolished Zn electrode
Reveal Answer
researching the scientific literature to determine how polishing changes the structure of Zn
While researching literature can provide background information, it is not an experimental method to directly test the student's specific hypothesis about the cell's current.
measuring the conductivity of a Zn electrode after polishing it
Measuring the conductivity of the zinc electrode alone does not measure the overall current produced by the electrochemical reactions in the galvanic cell.
measuring the change in mass per unit time of the Fe electrode in the same Fe–Zn galvanic cell before and after the Zn electrode was polished
The change in mass per unit time of the electrode is directly proportional to the cell's current. Using the same cell before and after polishing controls for confounding variables, making it the most valid experimental design.
measuring the current produced by two different Fe–Zn galvanic cells, one using a polished Zn electrode and the other using an unpolished Zn electrode
Although it directly measures current, using two different cells introduces confounding variables, such as slight differences in electrolyte concentration or internal resistance, which could affect the results.
Use the following information to answer the question.
A solution of citric acid, , was analysed by titration.
25.0 mL aliquots of the 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 solution.
The conical flask was rinsed with NaOH solution.
The conical flask was rinsed with 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 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 solution.
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.
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
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.