13.2 - Recording Results in a Table
What a table question looks like
- Most practical papers show instrument diagrams - a burette, a thermometer, a stop-clock - drawn at the readings a student took, and ask you to complete a table from them.
- A typical question: read a burette's final and initial readings and work out the volume added.
| final burette reading / cm3 | initial burette reading / cm3 | volume added / cm3 | |
|---|---|---|---|
| 18.8 | 4.2 |
What the examiner is marking
- Read each diagram correctly, to the precision that instrument allows.
- Do the calculation the table needs, such as final reading minus initial reading.
- Record every value in a column to the same number of decimal places.
A recurring instruction is that "all volumes and temperatures are recorded to one decimal place" - so five correct readings plus one given as a whole number (no decimal point) does not get full credit.
A typical question
A student titrates dilute sulfuric acid into aqueous potassium carbonate from a burette, using a suitable indicator. Complete the table by calculating the volume of dilute sulfuric acid added. [1]
Setting out the table
A results table is laid out as one table with one row per experiment, with columns arranged in a fixed order:
- A column for what was changed.
- One column for each instrument reading.
- A final column for anything worked out from them.
Examples of table layouts
| experiment | final burette reading / cm3 | initial burette reading / cm3 | volume of acid added / cm3 |
|---|---|---|---|
| 1 | 17.9 | 8.0 | 9.9 |
| 2 | 27.3 | 7.5 | 19.8 |
| length of magnesium ribbon / cm | initial temperature of acid / °C | highest temperature of acid / °C | temperature increase / °C |
|---|---|---|---|
| 1 | 25.0 | 25.0 | 0.0 |
| 5 | 25.0 | 35.0 | 10.0 |
| experiment | thermometer reading / °C | stop-clock reading / s |
|---|---|---|
| 1 | 19.0 | 91 |
| 5 | 52.0 | 31 |
Reading a burette, thermometer, and stop-clock
Each instrument has its own rule for how precisely it can be read.
The three instruments
- Burette - Graduated every 0.1 cm3; read the position of the liquid's meniscus against the scale. Accepted either to the nearest 0.1 cm3 or to the nearest 0.05 cm3 (interpolating half a division), but be consistent: all readings in a table to one decimal place, or all to the nearest 0.05 - never a mixture.
- Thermometer - Read to the nearest half of the smallest marked division. A thermometer marked in whole degrees is read to the nearest 0.5 °C, so a reading is 24.0 °C or 24.5 °C, never 24.3 °C.
- Stop-clock - Read to the nearest whole second, recorded in seconds only. One minute thirty seconds is recorded as 90 s, not 1:30 or 1 min 30 s.
Worked example
A rate experiment times a sudden colour change at five starting temperatures:
| experiment | temperature / °C | time / s |
|---|---|---|
| 1 | 19.0 | 91 |
| 2 | 34.0 | 54 |
| 3 | 41.5 | 43 |
| 4 | 46.0 | 36 |
| 5 | 52.0 | 31 |
Each temperature is read to the nearest 0.5 °C, matching the diagram's scale, and every time is a whole number of seconds.
Headings, units, and consistent precision
Column headings
- Write each heading as quantity followed by its unit, separated by a slash: volume / cm3, temperature / °C, time / s.
- The slash lets the numbers underneath be written as plain numbers, with no unit repeated next to every value.
Consistent precision
- Once you've decided how precisely an instrument is read, every value in that column must match.
- A thermometer column read to one decimal place: 30 °C is written 30.0, not 30 - the trailing zero shows the same precision was used throughout.
- The same applies to a calculated column: a temperature increase worked out from two one-decimal-place values is also given to one decimal place.
Common exam questions
Question 1
A burette diagram shows a reading between the 17 and 18 cm3 marks, roughly halfway. Which readings would both be accepted?
17.5 cm3 and 17.50 cm3 - a burette read is accepted either to the nearest 0.1 cm3 or to the nearest 0.05 cm3, as long as every reading in the table uses the same one of the two.
Question 2
A student completes four rows of a thermometer column as 25.0, 26.5, 28.0, 29.5, then writes the fifth as 31. Why might this lose a mark?
Because the fifth reading is not recorded to the same precision as the other four; it should be written as 31.0 to match the one decimal place used throughout the column.
Question 3
A stop-clock diagram shows one minute and fifteen seconds. How should this be recorded in a results table?
As 75 s - stop-clock and stopwatch readings are recorded in seconds only, not as minutes and seconds together.
Question 4
A table has columns for the initial burette reading, the final burette reading, and the volume added. A student completes the first two but leaves the third blank. What is missing?
The volume of acid added, found by subtracting the initial reading from the final reading - a calculated column still needs a value, worked out from the readings beside it.
Question 5
Why does a thermometer diagram sometimes get read to the nearest 0.5 °C and sometimes to the nearest 1 °C in different questions?
Because the precision depends on how finely that particular thermometer diagram is marked; a scale marked every 1 °C is read to the nearest 0.5 °C, while a scale marked every 2 °C is read to the nearest 1 °C, so you read the precision from the diagram given rather than assuming it.