NESA Chemistry Analysing Data and Information
5 sample questions with marking guides and sample answers · Avg. score: 92.3%
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.
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.
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 BaCl solution.
- Filter out the BaSO 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.
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.
Identify the independent and dependent variables.
Identify two control variables.
Describe a procedure for this investigation.
Outline the difference between systematic and random errors. Use an example of each from this investigation to support your answer.
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