AQA GCSE Chemistry (Triple) - Paper 2: Chemical Analysis

This set of flashcards covers key vocabulary and concepts related to chemical analysis as outlined in AQA GCSE Chemistry (Triple) Paper 2.

Pure Substance

A single element or compound not mixed with any other substance; it has a fixed melting point.

How to Identify a Pure Substance

It melts and boils at a specific, sharp temperature; impurities lower the melting point.

Formulation

A mixture designed to produce a useful product with specific properties, made in fixed proportions.

Examples of Formulations

Medicines, fuels, paints, cleaning agents, cosmetics, and alloys.

Mixture

Two or more substances not chemically bonded together; they can be separated by physical methods.

Chromatography

A technique used to separate and identify substances in a mixture based on how they move through a solvent.

Stationary Phase in Chromatography

The paper (or solid surface) that does not move.

Mobile Phase in Chromatography

The solvent that moves through the paper carrying the substances with it.

Why Different Substances Move Different Distances in Chromatography

Because they have different attractions to the paper (stationary phase) and solvent (mobile phase).

Chromatogram

Shows the separation of components in a mixture — each spot represents a different substance.

Identifying Substances with Chromatography

By comparing the position (Rf value) or colour of spots to known reference samples.

Difference on a Chromatogram Between Pure Substance and Mixture

A pure substance produces one spot; a mixture produces multiple spots.

Qualitative Analysis

Identifying what substances are present in a sample (not how much).

Quantitative Analysis

Measuring the amounts or concentrations of substances in a sample.

Common Tests for Gases

Hydrogen (squeaky pop with lit splint), oxygen (relights a glowing splint), carbon dioxide (limewater test).

Instrumental Analysis

Analytical methods that use instruments to detect and identify substances more accurately.

Examples of Instrumental Methods

Infrared spectroscopy, gas chromatography, and mass spectrometry.

Gas Chromatography (GC)

A technique to separate mixtures of gases or volatile liquids.

Gas Chromatography Linked To

Mass spectrometry — to identify substances after separation (GC-MS).

Mass Spectrometry

Shows the relative molecular mass (Mr) and structure of a compound by measuring the mass.

Advantages of Instrumental Methods

They are more accurate, faster, sensitive to very small amounts, and can be automated.

Disadvantages of Instrumental Methods

They require expensive equipment, trained operators, and interpretation of complex data.

Purpose of Baseline in Chromatography

It’s the starting line for the sample; drawn in pencil to prevent it dissolving in the solvent.

Importance of Solvent Front

It shows how far the solvent travelled, needed to interpret results.

Safety Precautions in Chemical Analysis

Avoid inhaling vapours, wear goggles and gloves, and handle reagents carefully.

Difference Between Physical and Chemical Tests

Physical tests do not change the sample (e.g., melting point), whereas chemical tests do.

Importance of Reproducibility in Analysis

It ensures results are reliable and can be compared across labs or tests.

Rf Value Conceptually

A ratio used to compare how far substances move in chromatography.

Chromatography and Purity

A single spot means pure; multiple spots mean a mixture.

Formulation Quality Testing

By checking that components stay in correct proportions and perform as intended.

Importance of Analytical Techniques in Modern Chemistry

They allow identification of unknown compounds in medicine, forensics, and environmental science.