8.2.3Additional lessons
Interpreting Results in Chemistry — IB Chemistry HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 172 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.
Part 1 of 6Describing the Data
Interpretation links what the data show to the research question.
Trend
- Trend State clearly how the dependent variable changes as the independent variable changes, using values from the data.
Pattern type
- Pattern type Say whether the relationship appears linear, curved, proportional or shows a plateau, based on the graph and not on prediction.
Outliers
- Outliers Identify any points that do not follow the trend and consider whether they affect the conclusion.
Support
- Support Quote specific values and refer to the graph so that each statement can be checked.
Part 2 of 6Linking to Theory
Linking to Theory
Explanation
- Explanation Use scientific principles, such as collision theory or Le Chatelier's principle, to explain why the trend happened.
Prediction
- Prediction Compare the result with the prediction and say whether it was supported.
Literature value
- Literature value Compare the experimental value with an accepted value and calculate the percentage error.
Limits
- Limits State the range of conditions over which the conclusion applies, and avoid extending it beyond the data.
Part 3 of 6Judging Reliability
1
Compare the percentage error with the total propagated uncertainty to see whether random error explains the difference.
2
If the error is larger than the uncertainty, look for systematic errors such as heat loss or incomplete reaction.
3
Discuss the effect of each weakness on the result, saying whether it makes the value too high or too low.
4
Identify the largest source of uncertainty and suggest a specific improvement for it.
5
Suggest an extension that would test the conclusion further.
Part 4 of 6Writing the Conclusion
Answer the question
- Answer the question The conclusion directly answers the research question and uses the quantitative result.
Evidence
- Evidence Support it with numbers from the data, the gradient, or the calculated value with its uncertainty.
Honest statements
- Honest statements Do not claim more than the data supports, and use words like 'suggests' where uncertainty is large.
Improvements
- Improvements Suggestions must be specific, such as using a polystyrene lid, rather than 'be more careful'.
Part 5 of 6Worked Example
Question
- An experimental enthalpy of neutralisation is −52 ± 7 kJ mol⁻¹ and the accepted value is −57 kJ mol⁻¹.
- Is the difference explained by uncertainty?
- Difference = 57 − 52 = 5 kJ mol⁻¹.
- Percentage error = 5 ÷ 57 × 100 = 8.8 %.
- The difference 5 kJ mol⁻¹ is smaller than the uncertainty of ±7 kJ mol⁻¹, so random uncertainty may account for it.
Answer
- Percentage error 8.8 %;
- the difference lies within the uncertainty
Part 6 of 6Exam Checklist & Tips
8.2.3 – Key Points for the Exam
- Trend The general direction in which the data change.
- Percentage error The difference between experimental and accepted values as a percentage of the accepted value.
- Systematic error A consistent error that shifts all results in one direction.
- Evaluation A judgement of the strengths and weaknesses of a method and its results.
- Extension A further experiment that would test or build on the conclusion.
Common Mistakes
- Stating a conclusion that is not supported by the data or that ignores the uncertainty.
- Giving vague improvements such as 'use better equipment' with no details.
- Explaining every difference from theory as 'human error' without evidence.
- Failing to say whether a weakness would make the result too high or too low.
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