Personal protective equipment and general rules
- Wear safety goggles whenever chemicals, glass or heat are in use. Eyes cannot be replaced.
- Wear a lab coat and closed shoes; tie back long hair and loose clothing.
- Use gloves for corrosive or toxic substances; wash hands after every practical.
- No food, drink or chewing gum in the lab.
- Keep bags off the floor and walkways clear.
- Never work alone and never do unplanned experiments.
- Know where the eyewash, safety shower, fire blanket, extinguisher and exits are.
Hazard symbols and risk assessment
Chemical labels use pictograms: a black symbol in a white square turned on its point with a red border. Common ones: flame (flammable), corrosion (burns skin, eats metal), skull and crossbones (toxic), exclamation mark (harmful or irritant), flame over circle (oxidiser, makes fires fiercer), health hazard, environment (harmful to water life) and gas cylinder.
A hazard is something that can cause harm (concentrated acid). A risk is how likely and how bad harm is in a given task. A risk assessment lists each hazard, what could go wrong, and how to lower the risk (use a dilute solution, smaller amounts, goggles, a fume cupboard).
Using apparatus: heating, measuring, weighing
Heating
Light the Bunsen burner with the air hole closed (yellow safety flame), then open it for a hot blue flame. Hold test tubes with a holder, fill them no more than one third, tilt them, heat gently near the top of the liquid and keep the mouth pointing away from people. Never heat a closed container. Hot glass looks the same as cold glass: let it cool.
Measuring liquids
Use a measuring cylinder, pipette (with a filler, never the mouth) or burette. Read at eye level from the bottom of the curved surface (the meniscus).
Weighing
Put a weighing boat on the electronic balance, press tare (zero), then add solid with a spatula. Record the mass with units (g).
Handling chemicals, accidents and waste
- Acid to water: diluting a strong acid gives out heat. Adding water to acid can boil the first drops and splash acid. Adding acid slowly to lots of water spreads the heat safely.
- Smell by wafting with your hand; never sniff directly. Never taste.
- Use a fume cupboard for toxic or smelly gases.
- Return stoppers to the right bottles; never put leftover chemicals back in the stock bottle.
- Accidents: report at once. Eye splash: eyewash for 10–15 minutes. Skin: rinse with lots of water. Burns: cool running water for 10+ minutes. Small fire: fire blanket or the right extinguisher; for burning clothes, stop, drop and roll.
- Waste: broken glass in the glass bin; heavy metals and organic solvents in marked containers, not down the sink. Using smaller amounts and safer chemicals is part of green chemistry.
How scientists plan a safe, fair experiment
- Ask a question and make a hypothesis (a testable guess).
- Choose the independent variable (what you change), the dependent variable (what you measure) and the control variables (what you keep the same, for a fair test).
- Write a method and a risk assessment.
- Collect data, repeat, and record in a table with units.
- Analyse (graphs, averages), conclude, and evaluate errors and improvements.
Key formulas and definitions
- Hazard = what can harm; Risk = chance × severity of harm in this task
- Add acid to water, never water to acid
- Test tube: ≤ 1/3 full, tilted, mouth away, heat gently
- Eye splash → eyewash 10–15 min; burn → cool running water 10+ min
- Fair test: change one variable, measure one, keep the rest the same
Worked examples
1. A bottle shows a flame pictogram. Where should you use it?
Far from any flame or spark. Turn off Bunsen burners nearby and keep the lid on. Flammable means it catches fire easily.
2. Write a mini risk assessment for diluting concentrated sulfuric acid.
Hazard: corrosive acid; heat is released. Risk: burns to skin or eyes from splashes. Control: goggles and gloves, add acid slowly to a large amount of water while stirring, work over a tray, have eyewash ready.
3. A student fills a test tube to the top and heats it at the bottom, pointing it at a friend. List three mistakes.
Too full (max one third); heated at the bottom (heat gently near the top of the liquid and move it, or it may shoot out); pointed at a person (point away).
4. In an experiment on how temperature affects how fast sugar dissolves, name the variables.
Independent: water temperature. Dependent: time to dissolve. Controls: mass of sugar, volume of water, stirring, type of sugar.
Common mistakes
- Adding water to concentrated acid. It can boil and splash; always add acid to water.
- Taking goggles off 'just for a moment' while others are still working.
- Pouring leftover chemicals back into the stock bottle, which contaminates it.
- Not reporting a small cut or spill because it seems minor.