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Hazards, risks and safety precautions

Edexcel IAL Chemistry · WCH13 Practical Skills in Chemistry I

You are expected to recognise hazard symbols and to give precautions that match a specific hazard. Generic answers such as 'wear safety glasses' rarely score on their own.

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Hazard and risk

A hazard is something that could cause harm (a corrosive acid, a flammable liquid, a toxic gas).
A risk is the chance of harm actually happening, which depends on how the substance is used.
A precaution reduces the risk. Always link it to the hazard: 'heat ethanol with an electric heater, not a Bunsen burner, because it is flammable'.

Symbol (red diamond)	Meaning	Examples
flame	flammable	ethanol, propanone, cyclohexane
flame over a circle	oxidising	potassium manganate(VII), potassium dichromate(VI), concentrated nitric acid
corrosion (liquid eating a hand and a surface)	corrosive	concentrated acids and alkalis, ethanoic anhydride, PCl5
skull and crossbones	acutely toxic	chlorine (high concentration), phenylamine
exclamation mark	harmful or irritant	moderately dilute acids and alkalis, many organic liquids
person with a starburst on the chest	serious health hazard (carcinogen, mutagen, sensitiser)	potassium dichromate(VI), some halogenoalkanes
dead tree and fish	hazardous to the environment	silver nitrate, copper(II) salts

GHS hazard symbols you should recognise.

Common hazards in AS practicals

Concentrated acids (HCl in Core Practical 6, sulfuric acid in halide tests): corrosive; wear gloves and eye protection; tests with concentrated H2SO4 in a fume cupboard on a small scale.
Diluting concentrated sulfuric acid: very exothermic; add the acid slowly to water, never water to acid, which can make it spit.
Toxic gases (Cl2, Br2 vapour, SO2, H2S, HCl, NO2): use a fume cupboard; never smell gases directly.
Flammable organics (ethanol, halogenoalkanes, ethers): no naked flames; use a water bath or electric heater.
PCl5: reacts violently with water, giving HCl fumes; use dry apparatus in a fume cupboard.
Oxidising agents (acidified dichromate(VI)): keep away from flammable materials; dichromate is also toxic and a carcinogen.

Writing a good precaution

1. Name the hazard and the substance.

2. State a precaution that controls that hazard.

3. If asked, say why it works.

Examples: 'Chlorine is toxic, so carry out the reaction in a fume cupboard.' 'The oxidation of propan-1-ol is very exothermic, so add the oxidising agent dropwise with cooling.'

Worked example

Give two hazards and matching precautions for the reaction of 2-methylpropan-2-ol with concentrated hydrochloric acid (Core Practical 6).

Concentrated HCl is corrosive and gives off HCl fumes: wear gloves and eye protection and use a fume cupboard.
2-methylpropan-2-ol and the product are flammable: keep away from naked flames.
Shaking in a separating funnel builds pressure: release it regularly by opening the tap with the funnel inverted.

Answer: Corrosive acid: gloves, goggles, fume cupboard. Flammable liquids: no flames. Pressure: vent the funnel.

Key idea: Hazard = could harm; risk = chance it will. Match each precaution to a named hazard. Fume cupboard for toxic gases, no flames for flammables, acid into water when diluting.

Check yourself

What does the exclamation mark hazard symbol mean?
- Toxic
- Oxidising
- Corrosive
- Harmful or irritant
Show answer
Harmful or irritant. The October 2021 report noted it was often mislabelled as 'toxic'.
What does a flame over a circle symbol mean?
- Flammable
- Oxidising
- Explosive
- Corrosive
Show answer
Oxidising. Oxidisers supply oxygen and make other materials burn more fiercely.
How should concentrated sulfuric acid be diluted?
- Add water quickly to the acid
- Add the acid to ice in a sealed flask
- Heat the acid before adding water
- Add the acid slowly to water, with stirring
Show answer
Add the acid slowly to water, with stirring. Dilution is very exothermic; adding acid to water keeps the mixture mostly water so it does not spit.
A reaction produces chlorine. What is the most important precaution?
- Carry it out in a fume cupboard because chlorine is toxic
- Wear a lab coat because chlorine is flammable
- Use a water bath because chlorine is explosive
- Use a larger flask
Show answer
Carry it out in a fume cupboard because chlorine is toxic. Chlorine is a toxic gas, so it must be removed from the room air.
Which hazard does the symbol of a person with a starburst on the chest show?
- Flammable
- Hazardous to the environment
- Serious long-term health hazard, such as a carcinogen
- Gas under pressure
Show answer
Serious long-term health hazard, such as a carcinogen. It covers carcinogens, mutagens and respiratory sensitisers. Candidates often missed it in 2025.
Which statement describes a risk rather than a hazard?
- The chance of being burned when heating ethanol near a naked flame
- Ethanol is flammable
- Concentrated acid is corrosive
- Chlorine is toxic
Show answer
The chance of being burned when heating ethanol near a naked flame. A hazard is the property; a risk is the likelihood of harm in a situation.
State a precaution, with its reason, for heating a mixture containing ethanol.
Show answer
Use a water bath or electric heater, not a naked flame, because ethanol is flammable.. Match the precaution to the hazard.

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Last updated 8 November 2026. Spotted a mistake? Tell us.