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Chemistry IA2 Rationale and Research Question Examples

QCAA Chemistry IA2 examples showing how to explain the rationale, modification and research question for gases and galvanic cell student experiments.

Updated 2026-05-22 · 5 min read

Quick answer

A strong Chemistry IA2 rationale does three jobs: it explains the chemistry theory, identifies a specific weakness in the original experiment, and justifies why the modified experiment will produce better evidence for a focused research question.

The examples below are adapted from two Sylligence-reviewed Chemistry IA2 drafts: a gases experiment about calcium carbonate and carbon dioxide, and a Daniell cell experiment about copper ion concentration and EMF.

What the rationale section is really doing

Your rationale should not read like a textbook chapter. It should build a chain of reasoning:

1. What chemical principle is being tested?
2. What did the original experiment investigate?
3. What was weak about the original method or evidence?
4. What modification fixes or extends that weakness?
5. What relationship should the modified experiment reveal?

For QCAA Chemistry IA2, the rationale is usually stronger when the modification is not random. The reader should be able to see why your new independent variable, dependent variable and controlled variables follow logically from the original practical.

Example 1: gases IA2 rationale

One gases exemplar started from an original magnesium and hydrochloric acid experiment that measured hydrogen gas volume. The student did not simply say they were changing reactants. They explained that the original experiment had a very small magnesium mass, one data point, high relative uncertainty and possible oxidation of magnesium before reaction.

The modified experiment then used calcium carbonate powder with excess hydrochloric acid to produce carbon dioxide. This made the modification stronger because:

• calcium carbonate could be measured in larger masses, reducing relative mass uncertainty
• powder increased surface area and helped the reaction complete more consistently
• varying mass produced a numerical trend instead of one isolated result
• the 1:1 mole ratio between calcium carbonate and carbon dioxide allowed molar volume to be tested

The rationale then linked the expected result to Avogadro's law: if temperature and pressure are controlled, increasing moles of gas should increase gas volume proportionally. That gave the student a clear reason to graph carbon dioxide volume against moles of calcium carbonate.

Example gases research question

A strong version of the research question would look like this:

How does increasing the mass of calcium carbonate reacted with excess hydrochloric acid affect the volume of carbon dioxide produced, and therefore the experimental molar volume of carbon dioxide at standard temperature and pressure?

This is effective because it names:

• independent variable: mass of calcium carbonate
• dependent variable: volume of carbon dioxide produced
• chemical system: calcium carbonate and hydrochloric acid
• purpose: estimating molar volume at STP
• implied controls: excess acid, pressure and temperature treatment

Example 2: galvanic cell IA2 rationale

Another exemplar modified a galvanic cell experiment. The original practical compared different half-cell combinations, which made the independent variable categorical. That meant the results could compare cells, but could not easily form a numerical trendline.

The modified experiment focused on one Daniell cell: zinc and copper half-cells. Instead of changing the metals, it varied copper ion concentration and measured EMF. This was a stronger IA2 design because:

• copper ion concentration is numerical and can be graphed
• the Daniell cell has a clear theoretical basis through standard electrode potentials
• the Nernst equation predicts a logarithmic relationship
• linearisation can be used to test the experimental trend against theory

The rationale also explained the chemistry: zinc is oxidised at the anode, copper ions are reduced at the cathode, and increasing copper ion concentration should increase the cathode's reduction tendency and therefore increase cell potential.

Example galvanic cell research question

A strong version of the research question would look like this:

How does increasing copper ion concentration in the copper half-cell affect the EMF generated by a Daniell cell with a fixed zinc ion concentration at room temperature?

This is effective because it avoids a vague question like "How do galvanic cells work?" It names the variable being changed, the response being measured and the cell conditions being controlled.

How to explain what you changed

| Section | What to write | Gases example | Galvanic cell example | |---|---|---|---| | Original weakness | Name the evidence problem | One magnesium mass produced no trend and high relative uncertainty | Different metal pairs produced categorical data | | Modification | Say what changed | Vary calcium carbonate mass and measure carbon dioxide | Vary copper ion concentration in one Daniell cell | | Chemistry reason | Link to theory | Avogadro's law predicts volume is proportional to moles | Nernst equation predicts EMF changes with concentration | | Evidence benefit | Explain why it improves IA2 | More data points allow a trendline and molar volume estimate | Numerical data allows graphing, linearisation and comparison to theory |

Common mistakes in the rationale

Avoid these patterns:

• explaining the chemistry theory without connecting it to the method
• saying "I changed the experiment to make it better" without naming the original limitation
• choosing an independent variable that cannot produce a clear trend
• writing a research question that does not include the chemical system
• claiming the modification improves validity or reliability without saying how

Use Sylligence for assignment feedback

If you have a Chemistry IA2 draft, Sylligence assignment feedback can help check whether your rationale, research question, modification, variables and evidence-quality explanation actually line up. Use it as feedback support before revising your own draft.

Sources

• QCAA Chemistry syllabus page
• QCAA Chemistry IA2 sample assessment instrument
• QCAA Chemistry 2025 subject report
• Chemistry LibreTexts: Galvanic cells/17%3A_Electrochemistry/17.02%3A_Galvanic_Cells)