Collecting Data in Chemistry (DP IB Chemistry): Revision Note
Collecting Data in Chemistry
This is the "doing" phase of your investigation where you perform the experiment you have carefully designed.
Your goal is to gather high-quality raw data that is both accurate and sufficient to answer your research question.
This involves making precise measurements and recording all relevant information, including both numbers and observations.
Principles of data collection
Collect and record sufficient relevant quantitative data
Quantitative data is numerical data that you measure in your experiment.
The foundation of your report is a raw data table.
This should be the first table you present and must contain only the direct measurements you take, with no calculations.
Designing your raw data table before you start is crucial.
A well-designed table must include:
A specific title that describes the experiment.
Clearly labelled columns for your independent and dependent variables.
Units and uncertainties in the column headers, not in the body of the table.
Data must be recorded to the correct precision of the instrument.
This is a common place where students lose marks.
For a burette marked to 0.1 cm³, readings must be recorded to two decimal places (e.g., 24.50 cm³), with the last digit being a 0 or a 5.
For a digital balance that reads to two decimal places, all masses must be recorded to two decimal places (e.g., 5.00 g, not 5 g).
Sufficient data means collecting enough data points to see a trend.
This includes:
Data for at least five increments of your independent variable.
At least three repeat trials for each increment to ensure reliability.
Identify and record relevant qualitative observations
Qualitative data is non-numerical data that you observe during the experiment.
These observations provide context and are crucial for your final analysis and evaluation.
Do not underestimate the importance of qualitative data.
It can help explain unexpected results or errors.
Examples of important qualitative data in chemistry include:
Colour changes (e.g., in a titration or when a precipitate is formed).
Effervescence (fizzing, indicating gas production).
Formation of a precipitate (a solid forming in a solution).
Formation of soot during combustion, indicating the reaction was incomplete.
Any noticeable temperature changes (e.g., a beaker feeling warm to the touch).
Identify and address issues that arise during data collection
Experiments do not always go perfectly to plan.
A key scientific skill is to notice and respond to issues as they happen.
If you encounter a problem, do not ignore it.
Record the issue in your lab notes.
Examples of issues and how to address them:
The reaction is too fast or slow:
You may need to adjust the concentration of a reactant to get a measurable rate.
Record the change and the reason for it.
An anomalous result (outlier):
If one of your repeat trials gives a result that is very different from the others, record it, and then conduct an additional trial to get a reliable set of concordant results.
Do not erase the outlier; you will justify its exclusion later.
Difficulty in judging an endpoint:
If the colour change in a titration is very gradual, make a note of this.
This is a limitation of your method that you will discuss in your evaluation.
Worked Example
Research question:
"What is the concentration of ethanoic acid in commercially sold vinegar?"
Quantitative data:
The raw data would be recorded in a table like the one below, showing all initial and final burette readings for each trial.
Trial | Initial burette reading / cm3 (±0.05) | Final burette reading / cm3 (±0.05) | Titre / cm3 (±0.10) |
|---|---|---|---|
Rough | 0.00 | 23.85 | 23.85 |
1 | 0.20 | 23.60 | 23.40 |
2 | 0.15 | 23.50 | 23.35 |
3 | 1.50 | 24.90 | 23.40 |
Qualitative data:
The ethanoic acid solution was colourless.
Upon addition of the phenolphthalein indicator, the solution remained colourless.
At the endpoint, the solution turned from colourless to a persistent, pale pink colour after the addition of a single drop of NaOH.
Worked Example
Research question:
"What is the effect of temperature on the rate of reaction between aqueous sodium thiosulfate and hydrochloric acid?"
Quantitative data:
The time taken for the reaction to complete would be recorded for each temperature in a table.
Temperature / °C (±0.1) | Time (Trial 1) / s (±0.2) | Time (Trial 2) / s (±0.2) | Time (Trial 3) / s (±0.2) |
|---|---|---|---|
20.0 | 125.4 | 124.9 | 125.8 |
30.0 | 62.1 | 63.0 | 62.5 |
40.0 | 31.5 | 30.9 | 31.2 |
50.0 | 15.8 | 16.1 | 15.5 |
60.0 | 8.1 | 10.9 (anomalous) | 8.3 |
Qualitative data:
As the reaction proceeded, a fine yellow precipitate of sulfur formed, making the solution increasingly opaque.
A faint, sharp smell of sulfur dioxide was detected.
Issue addressed during collection:
In the 60.0°C condition, trial 2 gave a time of 10.9 s, which was significantly different from trial 1 (8.1 s).
This was identified as a potential outlier, possibly due to a delay in starting the stopwatch.
A fourth trial was conducted which gave a time of 8.3 s, confirming the second trial was anomalous.
Examiner Tips and Tricks
Record raw data directly.
Never perform calculations in your head or on scrap paper.
Your raw data table must show the actual measurements you took (e.g., initial and final burette readings, not just the final titre).
Units and uncertainties belong in the headers.
This is the correct scientific convention and makes your tables clear and easy to read.
Avoid writing units after every number in the table body.
Your observations are evidence.
Don't treat qualitative data as an afterthought.
Good observations can be used as evidence in your conclusion and evaluation to explain why your results might differ from theoretical values (e.g., "incomplete combustion was observed via the formation of soot").
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