SQA Higher Chemistry Researching Chemistry: practical skills, apparatus, gravimetric analysis and the assignment

What Researching Chemistry actually demands

Researching Chemistry is the practical and investigative spine of SQA Higher Chemistry. Unlike the three content areas, it is not a body of facts to recall but a set of skills you apply: planning a fair, safe experiment, choosing the right apparatus, measuring substances by mass and by volume, and judging how trustworthy your results are. The SQA assesses these skills twice, in the question paper (applied to unfamiliar data and procedures) and in the assignment (your own experiment, written up under controlled conditions). This guide sets out each skill and the patterns the examiners reward.

Planning and hazard assessment

A valid plan starts with the variables: the independent variable you change, the dependent variable you measure, and the controlled variables kept constant so the test is fair. Reliability comes from repeating the experiment and averaging concordant results.

Hazard assessment is more than labelling something "dangerous". A hazard is the potential of a substance or procedure to cause harm; the risk is the chance of that harm under the conditions used. Marks come from naming a specific hazard (corrosive, toxic, flammable) and the control measure that reduces the risk (eye protection, fume cupboard, small quantities).

Common chemical apparatus

The examiners expect you to match apparatus to the precision a task needs.

• Approximate volumes: measuring cylinder, beaker.
• Accurate fixed volume: pipette (for example $25.0 \text{ cm}^3$).
• Accurate variable volume: burette, read to the bottom of the meniscus, to $0.05 \text{ cm}^3$.
• Making up a standard solution: volumetric (standard) flask.
• Accurate mass: electronic balance, often to three or four decimal places.

A titration is the classic test: use a pipette and a burette, never a measuring cylinder.

Gravimetric analysis

Gravimetric analysis finds a quantity by mass. The two methods you must know:

• Precipitation. A soluble ion is converted to an insoluble compound, which is filtered, dried and weighed. The mass of precipitate gives moles, and the mole ratio gives the original amount. For example, sulfate ions are precipitated as barium sulfate, $Ba^{2+}(aq) + SO_4^{2-}(aq) \rightarrow BaSO_4(s)$.
• Heating to constant mass. A hydrated solid is heated, cooled and reweighed repeatedly until two successive masses agree. The loss in mass is the mass of water of crystallisation driven off.

The phrase heating to constant mass is the marker of a careful method: you repeat the heat-cool-reweigh cycle until the mass no longer changes, proving the reaction is complete.

Volumetric analysis

Volumetric analysis (titration) finds an unknown concentration by reacting it with a standard solution of accurately known concentration until the reaction is just complete (the end point). The relationship $n = CV$ and the balanced equation turn the titre into a concentration. Only concordant titres (agreeing within about $0.2 \text{ cm}^3$) are averaged; a rough first run is ignored. This is covered in full on the chemical analysis page.

Accuracy, precision and reliability

These three words are not interchangeable:

• Accuracy - closeness to the true value (right apparatus and technique).
• Precision - closeness of repeats to each other (fine instruments, correct decimal places).
• Reliability - consistent, concordant repeats, so an average can be trusted.

A set of titres can be precise but inaccurate if a systematic error (such as an uncalibrated balance) shifts every reading the same way. Quoting answers to the correct number of significant figures, set by the least precise measurement, is part of good presentation.

The assignment

The assignment is worth 20 marks (scaled) and is a write-up of a candidate-chosen experiment under controlled conditions. It rewards a clear aim, valid raw data in headed tables with units, correct processing (calculations and graphs), analysis, an evaluation of the procedure with sources of error and improvements, and a conclusion linked to the underpinning chemistry. The same inquiry skills are examined in the question paper, so practising them here pays off twice.

How Researching Chemistry is examined

A typical SQA profile for these skills:

• Procedure design. Identifying variables, choosing apparatus, and improving reliability.
• Hazard reasoning. Naming a hazard and a matching control measure.
• Gravimetric calculation. Mass to moles to a formula or composition (water of crystallisation, percentage purity).
• Evaluation. Distinguishing accuracy, precision and reliability and suggesting improvements.

Check your knowledge

A mix of recall, calculation and evaluation questions. Attempt them, then check against the solutions.

1. Name the apparatus used to deliver a single accurate fixed volume. (1 mark)
2. Explain what is meant by heating a hydrated salt to constant mass. (1 mark)
3. State the difference between accuracy and precision. (2 marks)
4. A $3.59 \text{ g}$ hydrated salt leaves $1.76 \text{ g}$ of anhydrous salt ($GFM = 120.4$) after heating to constant mass. The water is $H_2O$ ($GFM = 18.0$). Find the moles of water per mole of salt. (3 marks)
5. Give one hazard and a matching control measure for handling a concentrated acid. (2 marks)