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Chemistry IA2 Limitations and Improvements Examples

Practical QCAA Chemistry IA2 examples for writing stronger limitations, effects and improvements in student experiment evaluations.

Updated 2026-05-22 · 5 min read

Quick answer

A strong Chemistry IA2 limitation names a specific method problem, explains whether it affects validity, reliability or accuracy, and proposes an improvement that directly fixes that problem. Generic lines like "human error" or "use better equipment" usually sound weak.

The examples below are adapted from two Sylligence-reviewed Chemistry IA2 drafts: a gases experiment and a galvanic cell experiment.

The limitation-effect-improvement chain

Use this structure:

| Part | What it must do | |---|---| | Limitation | Name the exact method or measurement issue | | Effect | Explain how it affected evidence quality | | Improvement | Propose a specific change that would reduce that exact issue |

Do not separate the improvement from the limitation. If the limitation is gas leakage, the improvement should address sealing or gas collection. If the limitation is serial dilution uncertainty, the improvement should address concentration preparation.

Gases IA2 examples

Gas syringe uncertainty

In the gases exemplar, the gas syringe had a large absolute uncertainty compared with smaller gas volumes. This mattered most at lower calcium carbonate masses, where a few millilitres of uncertainty became a large percentage of the measured carbon dioxide volume.

What this section did well:

• identified the specific instrument causing the uncertainty
• explained why the effect was larger at lower gas volumes
• linked the issue to reliability and precision
• proposed a lower-uncertainty gas collection method

A stronger improvement was to use a water-displacement method with a measuring cylinder that had smaller graduations. That directly reduced volume uncertainty instead of vaguely saying "use better equipment".

Trials across different days

The gases draft also recognised that trials collected across different days could introduce temperature and atmospheric pressure differences. Because gas volume depends on temperature and pressure, this would add variability before converting volumes to STP.

What this section did well:

• connected the limitation to the gas laws
• explained why the issue affects reliability
• proposed doing trials on the same day under controlled room conditions

Carbon dioxide leakage

The negative y-intercept and lower experimental gradient suggested carbon dioxide was consistently lost before measurement. That is a validity issue because the measured gas volume was systematically lower than the true gas volume.

Good improvements included:

• shortening the tubing path
• improving seals between the flask, tubing and syringe
• clamping connections more securely
• using lower-permeability tubing where practical

The key is that the improvement targets gas loss, not random measurement error.

Heat released by reaction

The calcium carbonate and hydrochloric acid reaction can release heat. If the gas is warmer than the measured room temperature, the STP conversion may use the wrong temperature assumption.

A useful improvement is to wait for the gas to reach thermal equilibrium before recording volume, or to measure the gas temperature more directly where possible. This links the improvement back to validity because the calculated STP volume depends on temperature.

Galvanic cell IA2 examples

Serial dilution uncertainty

In the galvanic cell exemplar, copper ion concentrations were prepared by dilution. Lower concentrations carried proportionally larger uncertainty, and repeated dilution steps could compound concentration error.

What this section did well:

• named the source of uncertainty
• explained why lower concentrations were more affected
• linked concentration uncertainty to EMF through the Nernst equation
• proposed volumetric pipettes and direct preparation from stock solution

Incomplete mixing

If the copper sulfate solution is not mixed properly, the copper ion concentration near the electrode may not represent the intended concentration. This creates random variation in EMF, especially at lower concentrations.

A matching improvement is to stir each solution with a magnetic stirrer for a fixed time before measurement. The fixed time matters because it makes the improvement repeatable.

Circuit resistance

The galvanic cell draft used the experimental y-intercept being lower than the theoretical standard cell potential as evidence of systematic EMF loss. This is a stronger evaluation move because it connects a graph feature to a method limitation.

Good improvements included:

• shorter, thicker conductive wires
• a lower-resistance salt bridge setup
• better electrical contact at terminals
• consistent electrode cleaning

Salt bridge contact with electrodes

If the salt bridge physically touches an electrode, ion migration can occur too close to the electrode surface and reduce the separation needed for the cell to maintain a strong potential difference.

A matching improvement is to clamp a rigid U-tube salt bridge so it remains in a fixed position and does not touch either electrode.

Weak versus strong wording

| Weak wording | Stronger wording | |---|---| | Human error affected results. | The gas syringe's +/-2 mL uncertainty produced high relative uncertainty at lower carbon dioxide volumes, reducing reliability. | | Use better equipment. | Replace the gas syringe with a water-displacement setup using a finer-graduation measuring cylinder to reduce absolute volume uncertainty. | | The circuit was not perfect. | Internal resistance in the wires and salt bridge lowered measured EMF below theoretical values, reducing validity. | | Mix it better. | Stir each copper sulfate solution for 30 seconds with a magnetic stirrer before measurement to reduce random variation in local copper ion concentration. |

Use Sylligence for assignment feedback

For Chemistry IA2, Sylligence assignment feedback can help check whether each limitation has a matching effect and improvement. That is often where drafts lose marks: the improvement sounds reasonable, but it does not actually fix the limitation being discussed.

Sources

• QCAA Chemistry syllabus page
• QCAA Chemistry IA2 sample assessment instrument
• QCAA Chemistry 2025 subject report
• Chemistry LibreTexts: The Nernst equation/16%3A_Electrochemistry/16.04%3A_The_Nernst_Equation)