Nearly every student writes “wear goggles and a lab coat” and nearly every student loses the mark. What examiners actually want is the thing you were protecting yourself from, and why the precaution deals with it.
📚 What you need to know
A hazard is the potential of a substance to cause harm, and it depends on the substance itself — mostly on its concentration.
A risk is the likelihood that harm actually happens, and it depends on how you use the substance.
Precautions such as goggles or a fume cupboard reduce the risk. They do not change the hazard.
Hazard warning symbols are shown in a red diamond on a white background; there are nine in the full set.
A risk assessment has three stages: identify the hazards, assess the risks, put control measures in place.
Control measures work best in order: eliminate, then substitute, then good practice and equipment, then PPE last.
You must also consider the environmental impact (waste, solvents, scale) and any ethical issues (consent, animals).
Hazard is not risk
These two words get used interchangeably in ordinary speech and they are not interchangeable here. Take hydrochloric acid. Concentrated, it is corrosive; moderately concentrated, it is an irritant; dilute, it is not classified as hazardous at all. That is the hazard, and it is a property of the bottle.
Now think about what you do with it. Pouring it into a burette held above your head is far more likely to end badly than filling the burette below eye level. Nothing about the acid changed — the risk did.
The only way to reduce the hazard is to change the substance itself — use a lower concentration, or a different chemical altogether.
If a question says “state the hazard”, name a property: corrosive, flammable, toxic. If it says “state the risk”, describe a situation: acid splashing into the eyes while the burette is filled. Getting these the wrong way round costs marks that cost nothing to keep.
Hazard warning symbols
Standardised symbols appear on labels and on safety data sheets so that the hazard is obvious without reading anything. They sit in a red diamond with a white background, and there are nine altogether. These are the ones you are most likely to meet.
Symbol
What it warns about
Typical example
Corrosive
burns skin and causes permanent eye damage
concentrated acids and alkalis
Health hazard
skin rashes, eye irritation, harmful if swallowed
many dilute laboratory solutions
Flammable
catches fire when heated or near a flame
ethanol, hexane, propanone
Acute toxicity
life-threatening even in small amounts
cyanide salts, methanol
Oxidising
may cause fire or explosion in contact with fuel
potassium manganate(VII), nitrates
Hazardous to the environment
a threat to aquatic life and ecosystems
heavy metal ions, halogenated solvents
Carrying out a risk assessment
🧩 The three stages
Identify the hazards. List every chemical you will use and every one you will produce, then note which are classified as hazardous.
Assess the risks. Judge how likely and how severe harm would be. Consider the amount used, whether it will be heated, the experience of the person doing it, and whether a gas is given off that could be inhaled. Grade each as low, medium or high.
Implement control measures. Choose precautions that bring each risk down to an acceptable level, and plan what to do if something is spilt.
Do not skip the products. A reaction can start with two harmless-looking solutions and generate a toxic gas, and it is the gas that determines whether the step belongs in a fume cupboard.
PPE is not wrong, it is simply the weakest measure. If a question asks you to reduce a risk, look for a change higher up the ladder first.
Every laboratory chemical has a material safety data sheet (MSDS). It lists the hazards, the safe handling conditions and what to do after a spill or exposure, and it is the proper source for a risk assessment — not memory. Anything you decant into another container must be labelled with the chemical name, its concentration and any hazard symbols.
Environmental impact
The investigation does not end when the results are recorded. Unused reactants and products have to go somewhere, and “down the sink” is often the wrong answer — heavy metal ions and halogenated solvents in particular are a threat to aquatic life.
Green chemistry is the framework for designing processes that avoid the problem rather than clean it up afterwards. There are twelve principles in the full set; these are the ones you can actually apply to a school investigation.
What you change
Why it helps
Work on a smaller scale (micro-scale apparatus)
less waste produced and less material at risk in a spill
Reduce volumes and concentrations of reagents
lowers the hazard as well as the amount of waste
Choose water or a simple alcohol as the solvent
avoids halogenated and highly volatile solvents
Use a catalyst where one exists
a lower temperature means less energy consumed
Reuse excess reactants and products
less new material has to be made or disposed of
Look at the atom economy of the route
a higher atom economy means fewer atoms end up as waste
Ethical considerations
These are less obvious in chemistry than in biology, but they still exist and the syllabus expects you to have thought about them. If human participants are involved in any way — even a taste test or a survey — you need their informed consent. If animals are involved, the established guidelines and protocols for animal experimentation must be followed.
WORKED EXAMPLE
Explain, using hydrochloric acid as an example, the difference between a hazard and a risk. State whether wearing eye protection changes the hazard, the risk, or both.
The hazardThe potential of the acid to cause harm, which comes from the substance itself. Concentrated HCl is corrosive; dilute HCl is not classified as hazardous.set by the chemical and its concentrationThe riskThe likelihood that harm actually occurs, which comes from how the acid is used: the volume, whether it is heated, and whether the burette is filled above eye level.set by the procedureThe eye protectionit reduces the risk onlyThe acid is exactly as corrosive as it was. All the goggles do is make it less likely to reach an eye.
WORKED EXAMPLE
A student plans to heat concentrated hydrochloric acid with manganese(IV) oxide, which releases chlorine gas. Suggest a suitable safety precaution and justify it.
Name the hazard firstChlorine gas is toxic and it is produced in the reaction, so the hazard comes from the product rather than the starting materials.Then the precautioncarry the reaction out in a fume cupboardThen the justificationThe fume cupboard draws the toxic gas away so that it cannot be inhaled, which reduces the risk of harm.“Wear goggles and a lab coat” would score nothing here. It is standard practice in any laboratory, and it does not address the gas.
WORKED EXAMPLE
An investigation uses 250 cm3 of 1.0 mol dm–3 copper(II) sulfate solution per trial. Suggest two changes that would reduce the environmental impact, and explain each.
Change 1 — scale it downRun the trials with micro-scale apparatus so that a fraction of the volume is needed.less copper-containing waste to dispose ofChange 2 — collect the wasteCopper ions are hazardous to aquatic life, so the solution should go into a labelled waste container for proper disposal, not down the sink.keeps heavy metal ions out of the water supplyA third option worth having ready: use a lower concentration, since that reduces the hazard as well as the waste.
💡 Exam tip
Define hazard by the substance and risk by the situation. One sentence each is enough.
Never give a bare precaution. Use the pattern: name the hazard, state the precaution, explain how it lowers the risk.
Include the products in a risk assessment, not just the reactants.
Reach for elimination or substitution before PPE when asked to reduce a risk.
For environmental questions, mention scale, concentration, solvent choice and disposal rather than a general appeal to being green.
Say informed consent for human participants; it is the phrase that earns the mark.
⚠️ Common mix-up
Using “hazard” and “risk” as synonyms. They are assessed as separate ideas and questions test the distinction directly.
Claiming goggles reduce the hazard. They reduce the risk; the chemical is unchanged.
Writing “wear a lab coat and goggles” as the answer to a safety question. That is assumed in every laboratory.
Assessing only the chemicals on the bench and forgetting a gas that the reaction will make.
Treating a dilute solution as automatically safe. The risk still depends on the volume, the temperature and how it is handled.
Up next: Measuring Variables — once the plan is safe, the question becomes whether the numbers it produces are any good. That comes down to choosing the right instrument and reading it properly.
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