IB Chemistry HL Internal Assessment Example

The research question is set within a specific kinetic context, linking copper(II) catalysis to luminol chemiluminescence and rate order, demonstrating strong contextualization.

Methodology description lacks justification for using mass in grams rather than mol dm⁻³. Converting to concentration and defending the choice would improve rigor.

The student provides a clear aim linking varying copper sulphate quantity to luminol reaction rate and light output, facilitating reproducibility and focus.

Introduction references bioluminescence via luciferin-luciferase which is different system from luminol. Clarify why luminol reaction is an appropriate model.

The background incorrectly states that reaction orders x and y will be zero universally. Clarify that x and y are determined experimentally and may be nonzero.

Mechanism discussion omits citation for the catalytic surface complex theory. Refer explicitly to Gates (2024) when describing active site blockage.

The hypothesis equation displays an unexplained term “[C_sH_N,Q_2]”. Ensure correct notation for reactant concentrations, for example [H₂O₂] and [luminol].

Control variables omit pH and bicarbonate concentration, which influence luminol chemiluminescence. Include and justify pH control in the variables section.

Key steps such as light sensor calibration and exact volume additions are missing. Adding these details will ensure the procedure can be fully reproduced.

The step numbering repeats “repeat steps 11–16 for each run 5 times”, conflating step indices. Clarify numbering to avoid procedural confusion.

The uncertainty propagation uses a simple sum (Δa=Δb+Δc) rather than root-sum-square. Apply the appropriate propagation formula for independent measurements.

Raw data table lacks propagated uncertainties for derived rates. Including uncertainties for time and illuminance differences improves the data recording communication.

Trial 5 at 0.200 g shows a much longer glow time (120 s) than other trials. Discuss this outlier and consider repeating that run to check for consistency.

Sample uncertainty calculation table sums percentage uncertainties incorrectly. Recalculate percentages and illustrate each step clearly.

The graph analysis uses an exponential fit rather than a log–log plot to determine order. For a power law, plot ln(rate) vs ln[CuSO₄] to extract n accurately.

The conclusion writes the rate law as Rate = k/CuSO₄ⁿ, which implies an inverse proportionality. Instead express as Rate = k[CuSO₄]ⁿ and note n<0 for inhibition.

Comparison to scientific context remains qualitative. Cite specific literature rate laws or catalytic inhibition constants to justify your fractional order.

Extension idea to determine order in respect to H₂O₂ is realistic and expands mechanism understanding. Consider designing that experiment in more detail.

Errors and improvements list specific issues but lacks analysis of their relative impact. Prioritize which systematic error most influences the rate order determination.