Every practical has a bit of risk in it, and the IB expects you to think about that before you pick anything up — not after something goes wrong. This page shows you how to spot a hazard, work out how risky it really is, and say something useful about it in an exam or your IA.
📘 What you need to know
A hazard is what a chemical or a piece of equipment can do to you. A risk is how likely that is to actually happen in your experiment.
Hazard symbols on a bottle warn you before you open it. You should recognise the common ones on sight.
A risk assessment is just three columns: the hazard, the risk, and the control measure you will use.
A control measure only earns marks if it matches the actual hazard. “Be careful” is worth nothing.
Ethical considerations cover animals, other people, and reporting your data honestly.
Environmental considerations cover safe disposal and using smaller amounts in the first place.
These ideas are examined on Paper 1 and Paper 2, and they are marked directly in your internal assessment.
Hazard is not the same as risk
Students mix these two words up constantly, and it costs marks. They are not the same thing at all.
A hazard belongs to the chemical. Concentrated hydrochloric acid is corrosive whether it is sitting on a shelf or in your hand. Nothing you do changes that.
A risk belongs to you and what you are doing. Pouring 100 cm3 of that acid on an open bench with no goggles is a huge risk. Using 2 cm3 of it, diluted, in a fume cupboard, with goggles on, is a small one. Same chemical, completely different risk.
That is why the third column matters. A control measure is the thing you change to pull the risk down — and it has to fit the hazard you named.
Work left to right every time. If you name a hazard but never say how you will control it, you have only done a third of the job.
The quickest way to test a control measure: read it back and ask “would this actually stop the thing I just described?” Goggles stop acid in the eye. Goggles do nothing about a flammable solvent near a Bunsen burner.
Reading the hazard symbols
Hazard symbols (the red-bordered diamonds, properly called GHS pictograms) are the fastest safety information you will ever get. They are on the bottle so you know what you are dealing with before you pour anything.
Symbol
What it means
Typical chemical
What you do about it
Flame
Flammable — catches fire easily
Ethanol, hexane, propanone
No naked flames. Heat with a water bath, not a Bunsen.
Skull and crossbones
Toxic — poisonous in small amounts
Methanol, cyanide salts
Fume cupboard, gloves, never mouth-pipette.
Liquid on a hand
Corrosive — destroys skin and eyes
Conc. HCl, conc. NaOH
Goggles and gloves. Dilute where the method allows.
Exclamation mark
Irritant or harmful
Dilute acids and alkalis
Goggles. Wash any splashes off straight away.
Circle over a flame
Oxidising — feeds a fire
Potassium manganate(VII)
Keep away from paper, solvents and fuels.
Dead fish and tree
Dangerous to the environment
Copper and lead salts
Never down the sink. Use the labelled waste bottle.
Worth knowing: the symbol tells you the hazard, but not how strong it is. Both 0.1 mol dm–3 and 12 mol dm–3 hydrochloric acid carry a warning symbol, and the difference between them is enormous. Always check the concentration too.
Writing a risk assessment that actually scores
A risk assessment is not an essay. It is a short, specific list. Vague safety writing is the single most common way students throw away easy marks in the IA.
🧩 Four steps to a risk assessment
List everything you will use. Chemicals, glassware, heat sources, electricity, and the substances you make during the reaction — a gas produced halfway through still counts.
Name the hazard for each one. Use the real word: corrosive, flammable, toxic, irritant, hot, sharp, under pressure.
Say how likely the harm is, given your amounts. Small volumes and dilute solutions genuinely lower the risk — say so.
Give a control measure that matches. One per hazard. Then add what you would do if it went wrong anyway.
WORKED EXAMPLE
Turning a weak safety line into one that scores
A student is heating ethanol with concentrated sulfuric acid to make ethoxyethane. Their risk assessment says: “Be careful with the chemicals and wear safety goggles.” Rewrite it properly.
Step 1: Split it into separate hazards
Ethanol — flammable. Conc. sulfuric acid — corrosive. Heating — burns and hot glass.
Step 2: Match a control to each oneEthanol: heat in a water bath, no naked flame anywhere near the bench.Acid: goggles and gloves; add the acid slowly to the ethanol, never the other way round.Heat: use a clamp, let glassware cool before you move it.Step 3: Add what you do if it goes wrong
Acid on skin → flood with cold water for 10 minutes, tell the teacher.
Three named hazards, three matching controls, one spill planthe original line named nothing, so it controlled nothing
Ethical considerations
Ethics in chemistry sounds like it belongs in another subject, but the IB means something quite concrete by it. It comes down to three things.
1. Living things
Any experiment involving animals, or human subjects, needs a serious justification and proper permission. If the same question can be answered without a living organism, you are expected to do it that way. In practice, for IB Chemistry, this usually means: don’t design an IA around feeding things to animals or taking samples from people.
2. People taking part
If your investigation involves other students — a taste test, a skin product, a survey — they need to know what they are agreeing to, they need to be able to stop at any point, and their personal data stays private.
3. Honesty with your data
This is the one that catches people out. Deleting a result because it “looks wrong”, nudging a titre so the numbers agree, or quietly not mentioning a repeat that disagreed — all of that is an ethical failure, not a small tidying-up job.
You are allowed to exclude an anomalous result. What you are not allowed to do is hide it. Show it, say why you think it happened, then say you excluded it. That is honest science and it reads far better than a suspiciously perfect table.
Looking after the environment
Two questions, in this order. First: can I use less? Halving the volumes usually halves the waste and the risk at the same time, and costs you nothing in the quality of your results. Second: where does this go at the end?
Copper and lead solutions are the ones students most often tip away without thinking. They are exactly the ones that must not go down the sink.
Using less in the first place
This is the idea behind green chemistry, and you can apply it to almost any school practical:
Scale down. A reaction that works in 50 cm3 usually works just as well in 10 cm3.
Swap the solvent. Water instead of an organic solvent wherever the chemistry allows it.
Use a catalyst. Lower temperature means less energy burnt to run the same reaction.
Recover what you can. Distil a solvent back and reuse it rather than pouring it away.
WORKED EXAMPLE
Choosing the disposal route
At the end of a practical a student has three beakers: (a) 40 cm3 of sodium chloride solution left over from a titration, (b) 30 cm3 of 1 mol dm–3 sulfuric acid, (c) 20 cm3 of blue copper(II) sulfate solution. How should each be dealt with?
(a) Sodium chloride solution
Salt water. Not toxic, not corrosive.
Sink, running the tap to dilute it → safe.(b) Sulfuric acid
Corrosive, and it would attack the drain pipework.
Add sodium carbonate until fizzing stops, check pH ≈ 7, then wash it away.(c) Copper(II) sulfate
Copper ions are toxic to aquatic life — the environment symbol.
Heavy metal waste bottle. Never the sink, however dilute the blue looks.Sink • neutralise then sink • waste bottle“it’s only a bit” is not a disposal method
💡 Exam tip
If a question says “state one safety precaution”, name the hazard as well as the action: “wear goggles, because dilute sodium hydroxide damages eyes”. The reason is usually where the mark sits.
Never write “be careful”, “handle with care” or “follow the instructions”. Those score nothing on any mark scheme.
Watch for the hazard that appears during the reaction, not at the start — a gas given off, a mixture that gets hot on its own.
Scaling down is a valid answer to both a safety question and an environmental one. Say it if it fits.
In the IA, safety, ethics and environment all live in the same criterion. A couple of specific sentences beats a page of general worry.
If you are asked to improve someone else’s method, look at their safety line first. It is very often the weakest thing in the whole plan.
⚠ Common mix-up
Saying “hazard” when you mean “risk”. The hazard belongs to the chemical, the risk belongs to what you do with it.
Giving a control that does not match. Goggles do nothing about a fire risk; a fume cupboard does nothing about a corrosive splash on your hand.
Forgetting the products. The mixture you make can be more hazardous than either thing you started with.
Assuming dilute means safe. Dilute acids and alkalis still damage eyes. Goggles stay on.
Pouring copper or lead solutions down the sink because they look harmless. They are the classic environmental error.
Treating ethics as only about animals. Honest handling of your own data is an ethical issue too, and it is the one you will actually meet.
Up next: Measuring Variables — picking what to change, what to measure, what to keep the same, and how to say honestly how good your numbers really are.
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