Chemistry Core Practicals — What You Need to Know
At least 15% of the marks on your Edexcel GCSE Chemistry exam papers are based on practical skills. This does not mean you carry out an experiment in the exam — it means you answer written questions about practical work. These questions draw on the core practicals specified in the Edexcel syllabus, plus general practical skills.
You must know each core practical thoroughly: the equipment, the method, the variables, likely results, and how to evaluate the procedure. This lesson gives you that overview.
The Edexcel Chemistry Core Practicals
The Edexcel GCSE Chemistry specification (1CH0) includes the following core practicals. These are the practicals that are explicitly named in the specification and are most likely to appear in exam questions.
Core Practical 1: Investigate the Effect of Concentration on Rate of Reaction
Context: This investigates how changing the concentration of hydrochloric acid affects the rate of its reaction with marble chips (calcium carbonate).
Equipment
- Conical flask, delivery tube, measuring cylinder, gas syringe or inverted measuring cylinder in water trough
- Marble chips (calcium carbonate, CaCO₃)
- Hydrochloric acid (HCl) at different concentrations
- Balance, stopwatch, safety goggles
Method Summary
- Measure a fixed mass of marble chips using a balance
- Measure a fixed volume of hydrochloric acid at a known concentration
- Add the acid to the marble chips in a conical flask
- Immediately connect the gas syringe or delivery tube
- Record the volume of gas (CO₂) produced at regular time intervals (e.g., every 30 seconds)
- Repeat with different concentrations of acid, keeping all other variables the same
Variables
| Variable | Detail |
|---|
| Independent | Concentration of hydrochloric acid |
| Dependent | Volume of gas produced (or time taken to produce a set volume) |
| Control | Mass and size of marble chips, volume of acid, temperature |
Key Exam Points
- The equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
- Higher concentration means more acid particles per unit volume, leading to more frequent collisions, so the rate is faster
- The total volume of gas produced is the same for each concentration (assuming the marble chips are the limiting reagent) — only the rate changes
- Using chips of the same size ensures a fair test (surface area is controlled)
Exam tip: A very common question asks you to explain why the same total volume of gas is collected regardless of concentration. The answer is that the marble chips are the limiting reagent — the same mass of chips produces the same amount of CO₂. Only the speed of the reaction changes.
Core Practical 2: Investigate the Separation of Substances Using Paper Chromatography
Context: This separates and identifies substances in a mixture (such as food colourings or inks) using paper chromatography.
Equipment
- Chromatography paper, beaker, pencil (not pen), ruler
- Solvent (water or ethanol depending on the substances)
- Samples of known and unknown substances
Method Summary
- Draw a pencil line near the bottom of the chromatography paper (the origin line)
- Place small spots of each substance on the pencil line, spaced apart
- Place the paper in a beaker containing a shallow layer of solvent (the solvent must be below the pencil line)
- Cover the beaker with a lid to prevent evaporation
- Wait for the solvent to travel up the paper (do not disturb)
- Remove the paper when the solvent front is near the top
- Mark the solvent front with a pencil immediately
- Measure distances and calculate Rf values
Variables
| Variable | Detail |
|---|
| Independent | The substance being tested |
| Dependent | Distance moved by each substance (Rf value) |
| Control | Type of chromatography paper, solvent, temperature, amount of substance applied |
Calculating Rf Values
Rf = distance moved by substance ÷ distance moved by solvent front
An unknown substance can be identified by comparing its Rf value with those of known substances run on the same chromatogram.
Exam tip: Always use a pencil for the origin line, never a pen. Pen ink would dissolve in the solvent and contaminate the results. This is a frequently asked question.
Core Practical 3: Preparation of Pure, Dry Hydrated Copper Sulfate Crystals
Context: Making a pure sample of copper sulfate crystals by reacting copper oxide (an insoluble base) with dilute sulfuric acid.
Equipment
- Beaker, Bunsen burner or water bath, glass stirring rod
- Copper oxide powder, dilute sulfuric acid
- Filter funnel, filter paper, conical flask
- Evaporating basin
Method Summary
- Warm the dilute sulfuric acid gently in a beaker
- Add copper oxide powder to the warm acid, stirring continuously
- Continue adding copper oxide until it is in excess (unreacted black powder remains at the bottom)
- Filter the mixture to remove excess copper oxide — the filtrate is copper sulfate solution
- Pour the filtrate into an evaporating basin
- Heat gently until crystals start to appear at the edges
- Leave to cool and crystallise at room temperature
- Pat dry with filter paper
Variables
| Variable | Detail |
|---|
| Independent | Not applicable (this is a preparation, not an investigation) |
| Dependent | Quality and purity of crystals |
| Control | N/A |
Key Exam Points
- Adding excess copper oxide ensures all the acid has reacted — this is crucial for purity
- Do NOT boil to dryness — slow evaporation produces better crystals
- The equation: CuO + H₂SO₄ → CuSO₄ + H₂O
Exam tip: This practical appears very frequently as a 6-mark question. Practise writing a full step-by-step method from memory — see Lesson 3 for a model answer.
Core Practical 4: Investigate Temperature Changes in Neutralisation Reactions
Context: Measuring the temperature change when an acid reacts with an alkali.
Equipment
- Polystyrene cup (as a calorimeter), thermometer, measuring cylinder
- Dilute hydrochloric acid, dilute sodium hydroxide solution
- Lid for the cup
Method Summary
- Measure a fixed volume of dilute hydrochloric acid into a polystyrene cup
- Record the initial temperature
- Add a measured volume of sodium hydroxide solution
- Stir and record the maximum temperature reached
- Calculate the temperature change (ΔT)
- Repeat with different volumes of alkali (keeping acid volume constant) to find the point of neutralisation
Variables
| Variable | Detail |
|---|
| Independent | Volume of sodium hydroxide added |
| Dependent | Temperature change |
| Control | Volume and concentration of acid, starting temperature, insulation |
Key Exam Points
- Neutralisation is exothermic — the temperature rises
- The maximum temperature change occurs at the exact point of neutralisation
- A polystyrene cup is used for insulation (reduces heat loss)
- The equation: HCl + NaOH → NaCl + H₂O