IB Chemistry HL Internal Assessment Example

The introduction clearly explains why molar mass and solubility are studied and situates the investigation in a scientific context. This establishes a solid foundation for the research question.

The student provides a coherent context linking molar mass and solubility to pharmaceutical and industrial applications but treats “common salts” too broadly. Narrowing the context to a specific salt family or application would strengthen the investigation’s relevance and specificity.

The secondary aim to identify salts opposing the hypothesis is stated, but the progression from aim to method could be clearer. Consider outlining how these salts will be analysed beyond identification.

The research question is precisely stated, articulating both the primary influence of molar mass on solubility and secondary factors like atomic radius and lattice enthalpy, which adds clarity and focus.

The control of “common salts” as a variable is vague. Define selection criteria (e.g., solubility range, ionic family) to justify the sample and ensure representativeness.

The description of methodology omits key details (e.g., specific CRC handbook pages, software or tools for plotting, and calculation steps for Pearson’s r). Adding these will ensure full reproducibility.

Citing the CRC Handbook as a data source demonstrates methodological consideration for data validity. Referencing the edition and year strengthens the credibility of the data.

Dependent and independent variables are defined with correct units (mol / kg and g / mol), which facilitates reproducibility and clarity in data collection.

The raw data table is well-structured with consistent units and significant figures, facilitating clear data communication. Consider adding row/column lines to improve readability.

The extensive raw data table on page 3 is valuable but could be split into two to reduce crowding. Consider grouping by cation family for clarity.

The rounding and significant-figure discussion shows awareness of precision but lacks numerical uncertainty estimates or propagation. Include error margins or uncertainties to strengthen quantitative rigor.

Relying solely on CRC Handbook reliability without quantified uncertainty is insufficient. Consider adding manufacturer or experimental error bars to indicate data variability.

The analysis notes that correlation does not imply causation, but the discussion could quantify the goodness-of-fit (e.g., R²) or perform a significance test to contextualize the correlation strength.

Figure 1 is clearly labelled with axes and units, ensuring that the negative correlation is immediately interpretable and visually accessible.

Calculating Pearson’s r (r≈−0.6727) correctly confirms the negative correlation. Explicitly stating the calculation tool or formula would complete the record of data processing.

The plot lacks error bars or confidence intervals around each point and the trendline. Including these would demonstrate appropriate consideration of uncertainties in the correlation.

Including specific numeric lattice enthalpy or hydration enthalpy values for the outliers would strengthen the causal argument linking ionic structure to solubility.

Part (ii) effectively identifies clear outliers to probe additional factors; this strategy strengthens the discussion by linking statistical deviations to chemical reasoning.

Outliers are chosen based on personal judgment without a clear threshold. Define quantitative criteria (e.g., distance from trendline) to ensure replicable outlier selection.

The conclusion that molar mass affects solubility is supported by data, but overgeneralizes by implying causation. Framing it as a trend rather than a direct cause would be more precise.

The discussion of ammonium nitrate’s low lattice enthalpy and ionic charge is chemically sound and well-explained, showing depth in evaluating factors beyond molar mass.

The analysis of sodium chloride and ammonium chloride is truncated and lacks detail on lattice enthalpy values. Completing this argument with quantitative enthalpy data would improve rigor.

Highlighting how lattice enthalpy links atomic radius and charge shows a strong understanding of interrelated factors, encouraging deeper theoretical integration.

The conclusion effectively synthesizes findings, noting that molar mass, lattice enthalpy, ionic charge, and atomic radius interplay to determine solubility trends.

The conclusion repeats that molar mass affects solubility but implies direct causation. Reframe as an observed trend and emphasize multifactorial influences to align with analysis.

The reflection sensibly proposes gathering more data and narrowing salt groups, which are realistic improvements. Specifying target sample sizes or experimental parameters would make these suggestions stronger.

Proposing multiple databases and experimental measurements is valuable, but the plan remains at a high level. Outline how experimental designs would be conducted to enhance feasibility.

The suggestion to perform experimental solubility measurements rather than relying solely on literature values is well-founded and would enhance data robustness.