IB Chemistry HL Internal Assessment Example

Background explains the structure of phenolphthalein and its pH-dependent colour change with correct chemical notation, strengthening the theoretical rationale.

The research question is clearly defined with specific variables, quantitative parameters, and an appropriate chemical context, enabling focused investigation.

The Beer–Lambert description omits mention of cuvette path length and stray-light correction; specify path length and calibration scope.

The pseudo-first-order justification is well articulated with citation, showing understanding of kinetic simplification under excess [OH⁻].

Table of chemicals omits purity of ethanol and supplier details; include these to ensure reproducibility.

Independent/dependent variables table should specify whether absorbance refers to maximum, post-mixing or both.

Justification of wavelength at 565 nm is clear, with correct use of absorbance principles and colour wheel arguments.

Using a 4 cm³ pipette to deliver 3 cm³ introduces ambiguity at lower volumes; a 3 cm³ pipette would reduce systematic error.

Controlled variables table is comprehensive and links each CV to control measures, demonstrating strong planning.

Drop volume of phenolphthalein is approximated; recommend validating drop size distribution or use micropipette for precision.

Funnel and cuvette are not pre-warmed, leading to heat loss; include a pre-heating step to reduce transfer cooling effects.

Methodology steps are detailed but omit timing between mixing and measurement, which may affect reproducibility.

Temperature control (CV10) is invoked multiple times in step annotations; consolidate references to avoid redundancy.

Equations for rate and k are correctly derived but units “nm s⁻¹” and “s⁻¹” should be explicitly annotated in processed tables.

The Maxwell–Boltzmann curve is included but lacks discussion of how error bars relate to energy distribution; link uncertainty to theory.

Calibration steps omit blank temperature specification; describe blank preparation conditions to standardize absorbance baseline.

Dilution calculation correctly applies C₁V₁=C₂V₂ and demonstrates sound preliminary work.

Uncertainty percentages are directly summed rather than using root-sum-square; revise propagation to improve accuracy.

Caption for Table 1 reads “Affect” instead of “Effect”; correct typographical error to maintain professionalism.

Sample graph coordinates use rounded 1/T value to two significant figures; maintain at least three SF to preserve regression accuracy.

Raw-data Table 1 combines uncertainties with trial structure and units effectively, facilitating transparent data recording.

Anomalous outliers (e.g. 1.02 at 5 °C) appear in raw-data; discuss whether to exclude or rationalize these points.

Some uncertainty values for ln(k) are inconsistent with propagated values; revisit calculations to ensure correctness.

A₁₂₀ table is well organized with clear uncertainty notation, enabling precise comparison across temperatures.

Processed uncertainties table is detailed and clearly communicates both absolute and percentage uncertainties.

Processed data Table 4 shows correct ΔA and k values but ΔA at 313 K appears inconsistent; verify raw subtractive values.

Column heading “ln ln(k)” is misleading; replace with “uncertainty in ln(k)” to match content.

Graph 1 regression displays maximum/minimum lines but fails to label which line corresponds to which uncertainty bound; clarify in legend.

The conclusion should explicitly state how the slope magnitude relates to activation energy and reference the calculated Eₐ.

Conclusion states inverse relationship but confuses axes: increasing 1/T yields lower ln k reflects positive k-T correlation; rephrase for clarity.

Link the 14.2% slope uncertainty to potential impact on Eₐ accuracy by describing how it propagates into the activation energy result.

Discussion of small error bars and precision is insightful, showing good grasp of measurement consistency.

R and R² interpretation is accurate and contextualizes the fit quality, enhancing the scientific discussion.

Suggestion to use micropipette for standardized drop sizes is valuable; include calibration procedure to ensure accuracy.

Systematic evaluation of heat loss during transfer is thorough; suggested funnel and cuvette pre-warming is well justified.

Recommendation to use larger volumes to reduce percentage uncertainty is realistic, but note potential effects on reaction kinetics.

Evaluation of random errors is comprehensive, with clear links between errors, impacts, and realistic mitigation steps.

Suggestion to position the water bath adjacent to the colourimeter reduces transfer delays; include expected transfer timing to quantify improvement.

Use of blank sample before each measurement addresses cuvette cleanliness; this is a practical and effective improvement.