Exercises: Analysis of data and sources

The table shows atmospheric $\mathrm{CO_2}$ concentration measured at an observatory.

Year	$\mathrm{CO_2}$ (ppm)
1980	339
2000	369
2020	414

1. a) Describe the trend shown.
2. b) Calculate the increase between 1980 and 2020.
3. c) Calculate the average increase per year over this period.

A student measures the pH of a stream at the same point on five days: 6.8, 7.0, 6.9, 7.1, 6.8.

1. a) Calculate the mean pH.
2. b) State the range of the data.
3. c) State what is meant by a reliable set of results.

Two sources give information on the safety of a food additive. Source A is a peer-reviewed journal article. Source B is a blog post by a company selling an alternative product.

1. a) State which source is more reliable.
2. b) Give two reasons for your answer.
3. c) Explain what is meant by bias.

Nitrate concentrations ($\text{mg}\,\text{L}^{-1}$) were measured in a river downstream of a farm: Mon 18, Tue 22, Wed 35, Thu 31, Fri 20. Heavy rain fell on Tuesday night.

1. a) Calculate the mean nitrate concentration.
2. b) Identify the peak value and suggest, using the rainfall information, an explanation.
3. c) The EU limit for drinking water is $50\,\text{mg}\,\text{L}^{-1}$ nitrate. Comment on the results.
4. d) Suggest one improvement to the sampling design.

A news headline states: "Chemical X in tap water causes illness." The report gives that among 20 people who drank water with X, 3 became ill, and no control group was studied.

1. a) Calculate the percentage who became ill.
2. b) Explain why the lack of a control group prevents a conclusion about cause.
3. c) Suggest how a better study could be designed.
4. d) Distinguish between correlation and causation.

A graph of a titration of a monoprotic acid with sodium hydroxide gives an equivalence point at $24.6\,\text{cm}^3$ of $0.100\,\text{M}$ NaOH for a $25.0\,\text{cm}^3$ acid sample.

1. a) Calculate the concentration of the acid.
2. b) The manufacturer states the concentration is $0.105\,\text{M}$. Calculate the percentage difference from the stated value.
3. c) Suggest two possible sources of experimental error.
4. d) State what you would do to improve confidence in the result.

Two reports estimate the effect of a new wastewater plant on a lake. Report 1 (by the council) states average phosphate fell from $80$ to $55\,\mu\text{g}\,\text{L}^{-1}$ using monthly samples over 3 years at four sites. Report 2 (by a campaign group) states that phosphate "remains dangerously high" using one sample taken after a storm at one site.

1. a) Calculate the percentage reduction in Report 1.
2. b) Evaluate the validity and reliability of each report.
3. c) Identify possible bias in each.
4. d) Describe the further data you would need to conclude whether the plant is effective.

A student claims that "the rate of reaction doubles for every $10\,^{\circ}\text{C}$ rise". The student's data for the time to complete a reaction are:

Temperature (°C)	20	30	40	50
Time (s)	160	82	38	21

1. a) Calculate the relative rate ($1/t$, in $\text{s}^{-1}$) at each temperature.
2. b) Calculate the ratio of rates for each $10\,^{\circ}\text{C}$ step.
3. c) Evaluate the student's claim, using the data.
4. d) Explain, using collision theory, why rate increases with temperature, and why the claim is only an approximate rule.

An article claims that a new "green" fuel is carbon neutral. It provides: the fuel is made from waste cooking oil; production consumes electricity from a grid that is 40% fossil-fuelled; and combustion releases $2.4\,\text{kg}$ of $\mathrm{CO_2}$ per litre, of which the article says all is "recycled" by the oil-producing plants.

1. a) Identify the assumptions behind the claim of carbon neutrality.
2. b) Explain why the electricity used in production affects the claim.
3. c) Suggest what additional data would allow a life-cycle assessment.
4. d) Write a balanced conclusion on whether the claim is justified on the evidence given.