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Chemistry IA Exemplar: Sodium Thiosulfate and Hydrochloric Acid… | RevisionDojo
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IB Chemistry HL Internal Assessment Example
What is the order of reaction with respect to sodium thiosulfate and hydrochloric acid in their reaction, as determined by varying concentrations of each reactant(while the other is kept consistent) and measuring the time taken for sulfur to precipitate, changing the solution from clear to opaque?
4
Official IB Result
12/24
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12/24
0
12
24
5.1·Suggestion
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Procedure steps are detailed but repetitive; consider summarizing repeated actions to improve clarity and conciseness.
Criteria A: Research Design
5/6
0
3
6
Criteria Strands
Excellent
Research question context
Good
Methodological considerations
Good
Methodology description
Criteria Feedback
Research question framed within a specific chemical-kinetics context, clearly linking both reactants and the measurement approach.
Dilution calculations are clearly shown with correct formula and sample computations, enabling reproducibility.
Materials table is comprehensive with listed uncertainties, facilitating a robust uncertainty analysis.
Design adapts to minimise waste and hazard by scaling down volumes and reducing acid concentration.
Inline citation appears incomplete; sources need full referencing to maintain academic rigor.
Rationale for selecting concentration ranges lacks explanation of how these ensure sufficient coverage of reaction rates.
End-point determination via visual obscurity (‘X’) is subjective; define a quantifiable opacity threshold or use an instrument.
Clarify how total volume standardization to 30 cm³ is maintained when varying reactant and water volumes.
1.1·Strength
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The student has framed the research question within a specific chemical-kinetics context, clearly linking both reactants and the measurement approach for reaction order determination.
1.2·Suggestion
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The inline citation appears incomplete; ensure citations are formatted correctly and sources are fully referenced to maintain academic rigor.
1.3·Suggestion
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Rationale for selecting concentration ranges could be strengthened by explaining why chosen values ensure sufficient coverage of the reaction rate range.
1.4·Weakness
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End-point determination by visual obscurity of the “X” is subjective; define a more quantifiable opacity threshold or use an instrumental measure of turbidity.
1.5·Suggestion
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Clarify how total volume standardization to 30 cm³ is maintained across different reactant and water volumes to avoid ambiguity in dilution.
1.6·Strength
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Materials table is comprehensive with listed uncertainties, facilitating a robust uncertainty analysis in subsequent data processing.
1.7·Strength
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The student has thoughtfully adapted the design to minimise waste and hazard by scaling down total volumes and reducing acid concentration.
1.8·Suggestion
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Safety table outlines hazards well, but disposal of acid should specify neutralization steps to meet standard laboratory safety protocols.
1.9·Strength
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Dilution calculations are clearly shown with correct formula and sample computations, enabling reproducibility and transparency.
Criteria B: Data Analysis
2/6
0
3
6
Criteria Strands
Good
Communication of data recording and processing
Poor
Consideration of uncertainties
Moderate
Data processing quality
Criteria Feedback
Raw data tables include explicit uncertainties and multiple trials, supporting reliable averaging and error tracking.
Graphs of concentration versus time are clear, well-labeled, and effectively display expected kinetic decay profiles.
Uncertainty propagation is limited to a single example; no propagation into rate calculations or error bars on graphs.
The formula for reaction order is applied incorrectly (ln(rate₂ + rate₁) instead of ln(rate₂/rate₁)), leading to flawed analysis.
Table headers are incomplete in places, and some processed tables are mis-titled, reducing clarity.
Outliers in HCl trials are not discussed or justified, undermining data reliability.
2.1·Weakness
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Table header for Experiment I is empty and lacks column definitions; include all headers to communicate data structure clearly.
2.2·Suggestion
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Include a quantitative description of image observations (e.g., pixel intensity change) to support qualitative data analysis.
2.3·Strength
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Raw data includes explicit uncertainties and multiple trials, supporting reliable averaging and error propagation.
2.4·Weakness
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Data for HCl trials show significant outliers (e.g., 314 s, 462 s); discuss exclusion criteria or repeat anomalous trials to justify data reliability.
2.5·Weakness
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Reaction rates are rounded to two significant figures; ensure consistency with raw-data uncertainties and consider three-figure precision where justified.
2.6·Weakness
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Formula incorrectly uses ln(Rate₂ + Rate₁) instead of ln(Rate₂ ÷ Rate₁); correct expression is n=ln([A]2/[A]1)ln(Rate2/Rate1).
2.7·Strength
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Graphs of concentration vs time are clear, well-labeled, and effectively display expected kinetic decay profiles.
2.8·Suggestion
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Consider adding error bars or confidence intervals to the graphs to reflect experimental uncertainties and improve precision of linear fits.
Criteria C: Conclusion
3/6
0
3
6
Criteria Strands
Good
Conclusion relevance and support
Moderate
Scientific context comparison
Criteria Feedback
The conclusion that the reaction is first order in each reactant is linked to the observed doubling-time behavior and supported by tables and graphs.
Calculation and reporting of percentage error against theoretical values are correctly carried out, aiding interpretation.
Fractional order (e.g., 0.557) is rounded to one order without justification; the report should acknowledge or justify any rounding of non-integer orders.
Comparison to the wider scientific context is superficial; no literature values or mechanistic implications are explored.
Discussion of anomalous HCl data fit (R² and scatter) could inform a deeper interpretation but is not fully developed.
3.1·Weakness
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Interpretation rounds 0.557 up to first order; acknowledge this is a fractional order and justify any rounding or report as fractional to reflect data.
3.2·Strength
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Calculation of percentage error is correctly applied using absolute difference, enhancing interpretation against theoretical first-order values.
3.3·Weakness
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Conclusion restates methods but lacks discussion of mechanistic implications; expand on how observed orders inform the reaction mechanism.
Criteria D: Evaluation
2/6
0
3
6
Criteria Strands
Poor
Methodological weaknesses
Moderate
Suggested improvements
Criteria Feedback
Suggestions for frame-by-frame video analysis demonstrate an insightful approach to reducing timing uncertainty.
Identifies relevant pragmatic improvements such as enhanced temperature control and video analysis to improve data reliability.
Evaluation lists methodological weaknesses in generic terms without analysing their relative impact on results.
Descriptions of improvements are brief and lack quantitative development or specific implementation details.
The practical effect of proposed changes (e.g., temperature control) on uncertainty reduction is not evaluated.
4.1·Weakness
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Graph for HCl reaction rate exhibits less linearity (R²=0.865); discuss potential causes of scatter and its impact on order determination.
4.2·Strength
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Discussion effectively compares R² values to assess linearity and precision differences between experimental runs.
4.3·Suggestion
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Evaluate temperature control explicitly; measure or maintain reaction temperature to reduce variability in rate measurements.
4.4·Strength
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Proposal to implement frame-by-frame video analysis demonstrates an insightful approach to reducing timing uncertainty and improving accuracy.
