Recording data, significant figures and anomalies

Tables

• Column headings give the quantity and unit, separated by a slash: 'volume of gas / cm³'. Units do not go in the body of the table.
• Each column uses the same number of decimal places, matching the apparatus. Burette readings are written to 2 d.p. ending in 0 or 5, such as 24.05 or 0.00.
• Record raw readings (initial and final burette readings, both masses) as well as the processed values.

Significant figures

• Give a final answer to the same number of significant figures as the least precise measurement used, usually 2 or 3. Pearson's example: a temperature rise of 8.5 °C (2 s.f.) means ΔH = -52.345 kJ mol^-1 is written as -52 kJ mol^-1.
• Keep full figures in your calculator part-way through and round only at the end.
• Leading zeros are not significant (0.0205 has 3 s.f.); zeros after a decimal point at the end are (0.02050 has 4 s.f.).

Means, concordance and anomalies

• In titrations, the first (rough) titre shows roughly where the end point is and is not used. Repeat until you have concordant titres, which agree closely (Pearson mark schemes count titres within 0.20 cm³ of each other as concordant; use the tolerance the question gives if it states one). The mean uses only concordant titres.
• An anomalous result does not fit the pattern. Leave it out of the mean and ignore it when drawing a line of best fit.
• If the other results already show a clear pattern, you do not need to repeat the experiment because of one anomaly (October 2021 examiners' report).

Worked example

Titres (cm³): rough 24.90, then 24.25, 24.60 and 24.35. Concordant means within 0.20 cm³. Find the mean titre.

1. Ignore the rough titre.
2. 24.25 and 24.35 agree within 0.20 cm³; 24.60 is 0.25 cm³ from 24.35, so it is not concordant.
3. Mean = (24.25 + 24.35) / 2 = 24.30 cm³

Answer: 24.30 cm³

Check yourself

1. Titres (cm³) after a rough run: 23.45, 23.80 and 23.55. Concordant titres agree within 0.20 cm³. Calculate the mean titre.
   Show answer

   23.50 cm³. 23.80 is not concordant. Mean = (23.45 + 23.55) / 2 = 23.50 cm³.

2. Which is a correctly recorded burette reading?
   • 24.1 cm³
   • 24.050 cm³
   • 24 cm³
   • 24.05 cm³
   Show answer

   24.05 cm³. Burettes are read to 0.05 cm³ and recorded to 2 d.p.

3. How many significant figures are there in 0.02050?
   Show answer

   4. Leading zeros do not count; 2, 0, 5 and the final 0 do.

4. A mass of 1.25 g and a temperature rise of 8.5 °C are used to calculate an enthalpy change. To how many significant figures should the answer be given?
   • 3
   • 4
   • 2
   • 1
   Show answer

   2. The least precise measurement (8.5 °C) has 2 significant figures.

5. Which is the best column heading?
   • volume of gas / cm³
   • volume of gas
   • cm³
   • gas (cm³ per reading)
   Show answer

   volume of gas / cm³. Quantity, then a slash, then the unit.

6. An enthalpy change is calculated as -52.345 kJ mol^-1 from data whose least precise value has 2 significant figures. Give the answer to the correct precision.
   Show answer

   -52 kJ mol^-1. Round to 2 s.f.: -52 kJ mol^-1.

7. One point on a graph is clearly off an otherwise smooth curve. What should you do when drawing the line of best fit?
   • Ignore the anomalous point and draw the curve through the others
   • Make the curve pass through it
   • Join every point with straight lines
   • Start the experiment again
   Show answer

   Ignore the anomalous point and draw the curve through the others. Anomalies are not included in the line of best fit; a repeat is not needed if the pattern is clear.

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Sources

• Pearson Edexcel IAL Chemistry (2018) specification
• Pearson IAL Chemistry teacher practical guide
• Pearson examiners' report, WCH13 October 2021

Last updated 8 November 2026. Spotted a mistake? Tell us.