8.2.1Additional lessons
Collecting Data in Chemistry — IB Chemistry HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 170 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Types of Data
Good data collection makes processing and evaluation possible later.
Quantitative
- Quantitative Numerical measurements such as masses, volumes, temperatures and times, recorded to the precision of the instrument.
Qualitative
- Qualitative Descriptive observations such as colour changes, the formation of a precipitate, bubbles or smell, written objectively.
Raw data
- Raw data These are the measurements as they were originally recorded, before any calculation or rounding.
Processed data
- Processed data Values obtained by calculation from raw data, such as a mean or a rate.
Section 2 of 5Recording Results
Recording Results
Tables
- Tables Each column has a heading with the quantity, its unit and the uncertainty, so the units do not need repeating in every cell.
Decimal places
- Decimal places Every value in a column is recorded to the same number of decimal places, matching the precision of the instrument.
Observations
- Observations Write what was seen, such as 'a white precipitate formed', and not an interpretation such as 'silver chloride formed'.
Order
- Order Record readings immediately in the table, not on loose paper, to keep the original data.
Section 3 of 5Collecting Enough Data
1
Take at least five values of the independent variable over a suitable range.
2
Repeat each measurement at least three times to estimate the random variation.
3
Check repeat values as you collect them and repeat a trial if one result is clearly out of line.
4
Take readings at suitable intervals so that changes, especially fast ones, are properly captured.
5
Note any problem during an experiment, such as a spill or a delay, as it may explain odd results.
Section 4 of 5Outliers and Anomalies
Identify
- Identify An anomalous result is far from the others and is spotted by comparing repeats.
Record
- Record Never delete an anomaly from the raw data table; mark it clearly and explain why it is questionable.
Exclusion
- Exclusion If there is a clear cause, the point is excluded from processing, and the reason is stated.
Repeat
- Repeat Repeating the trial is better than discarding it, if time and materials allow.
Section 5 of 5Exam Checklist & Tips
8.2.1 – Key Points for the Exam
- Raw data Measurements recorded directly during an experiment, before processing.
- Qualitative data Descriptive observations that are not numerical.
- Quantitative data Numerical measurements with units.
- Anomaly A result that does not fit the pattern of the rest of the data.
- Replicate One of several repeated measurements under the same conditions.
Common Mistakes
- Recording interpretations, such as 'chlorine was produced', instead of observations such as a green-yellow gas.
- Writing data to different numbers of decimal places in the same column.
- Rubbing out an anomalous reading instead of marking it and explaining it.
- Leaving out units or uncertainties in table headings.
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