Unit 2 Laboratory safety and apparatus
Key unit competence: Use effectively laboratory equipment and materials to carry out experiments.
Key ideas
- A chemistry laboratory is a room equipped for carrying out experiments safely; it has benches, sinks, gas taps, fume cupboard, fire extinguishers, first-aid kit and safety equipment.
- Key safety rules: never eat, drink or taste chemicals; wear a lab coat and goggles; tie back long hair; never point a heated test tube at anyone; report every accident or breakage to the teacher.
- Hazard symbols warn about danger: flammable (flame), corrosive (liquid eating a hand and metal), toxic (skull and crossbones), harmful/irritant (exclamation mark), oxidising (flame over a circle), explosive and environmental hazard.
- Heating apparatus: Bunsen burner, spirit lamp, tripod stand, wire gauze, crucible, evaporating dish. A Bunsen burner gives a hot blue (non-luminous) flame when the air hole is open and a yellow (luminous) sooty flame when it is closed.
- Measuring apparatus: measuring cylinder (volume), burette and pipette (accurate volumes), thermometer (temperature), balance (mass), stop-watch (time). Read the volume at the bottom of the meniscus, with the eye level with it.
- Holding and containing apparatus: test tube, boiling tube, beaker, conical flask, round-bottomed flask, test-tube holder, test-tube rack, clamp and stand, spatula, dropper, filter funnel.
Common misconceptions
- "A yellow flame is hotter than a blue flame." No: The blue (non-luminous) flame, with the air hole open, is hotter and cleaner.
- "You can smell a gas by putting your nose over the test tube." No: Waft the gas gently towards your nose with your hand.
- "Water should be added to concentrated acid." No: Always add acid slowly to water, never water to acid, to avoid violent spitting.
Worked examples
Example 1. A burette reads 0.50 cm3 before a titration and 24.70 cm3 after. What volume of solution was used?
Solution
Volume used = final reading − initial reading
= 24.70 − 0.50
= 24.20 cm3.
Example 2. Explain why goggles, a lab coat and tied-back hair are needed when heating chemicals.
Solution
Goggles protect the eyes from splashes and hot particles.
A lab coat protects skin and clothes from spills.
Tied-back hair cannot catch fire in the Bunsen flame or dip into chemicals.
Practice questions
Name the apparatus used to hold a test tube while heating it.
Show answer
Test-tube holder.
Common mistake: Writing 'tongs', which are used for crucibles and hot solids.
State two uses of a Bunsen burner.
Show answer
Heating substances; boiling liquids; sterilising (any two).
Common mistake: Saying it is used to light the room.
What does a flame symbol on a bottle mean?
Show answer
The substance is flammable (catches fire easily).
Common mistake: Confusing it with the oxidising symbol, a flame over a circle.
Why should you never return unused chemicals to the stock bottle?
Show answer
They may have been contaminated and would spoil the whole stock.
Common mistake: Saying it is simply wasteful.
A measuring cylinder reading is 35.5 cm3 before and 18.0 cm3 after pouring some liquid out. What volume was poured?
Show answer
35.5 − 18.0 = 17.5 cm3.
Common mistake: Adding the two readings instead of subtracting.
Give two differences between a luminous and a non-luminous flame.
Show answer
Luminous: yellow, cooler, sooty, air hole closed. Non-luminous: blue, hotter, clean, air hole open (any two pairs).
Common mistake: Saying the yellow flame is hotter.
Explain why acid is added to water and not water to acid.
Show answer
Mixing gives out much heat; adding acid to a large volume of water spreads the heat and prevents boiling and spitting.
Common mistake: Saying acid is lighter than water.
Which apparatus would you use to evaporate water from a salt solution?
Show answer
An evaporating dish on a tripod and gauze, heated with a Bunsen burner.
Common mistake: Using a measuring cylinder, which must never be heated.
Why must broken glass be put in a special bin and not in an ordinary basket?
Show answer
Sharp glass can cut cleaners; a labelled glass bin keeps people safe.
Common mistake: Saying the glass can be reused immediately.
A pipette is more accurate than a measuring cylinder. Explain what this means for an experiment.
Show answer
The pipette gives a volume closer to the true value, so results are more reliable.
Common mistake: Thinking accuracy means delivering a larger volume.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Which apparatus is used to pick up small amounts of solid chemicals? a. Burette 2. Which flame is produced when the air hole of a Bunsen burner is fully open? b. add the acid slowly to water while stirring 3. The correct way to dilute concentrated sulfuric acid is to: c. Spatula 4. Which apparatus is the most accurate for measuring a volume of 23.4 cm3 during a titration? d. Blue, non-luminous, very hot flame Show answer
1 → c (Spatula) · 2 → d (Blue, non-luminous, very hot flame) · 3 → b (add the acid slowly to water while stirring) · 4 → a (Burette)
- A spatula is a small flat spoon used to transfer solids.
- With enough air, the gas burns completely, giving a hot blue flame.
- Adding acid to water lets the heat spread safely; water added to acid can boil and spit.
- A burette is graduated to 0.1 cm3 and delivers variable, accurate volumes.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
oxidising substances · corrosive · toxic · harmless- A skull and crossbones hazard symbol means the substance is .
- A flame over a circle is the symbol for .
- The hazard symbol showing a liquid eating through a hand and a metal means .
Show answer
1: toxic · 2: oxidising substances · 3: corrosive
- The skull and crossbones warns that the substance is poisonous (toxic).
- Oxidising substances give oxygen and make other materials burn more fiercely.
- Corrosive substances, such as concentrated acids, destroy skin and metals.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Which apparatus measures the temperature of a liquid? a. Thermometer 2. Which piece of apparatus is used to measure the volume of a liquid roughly? b. Pipette 3. Which apparatus is used to deliver a fixed, accurate volume such as 25.0 cm3? c. Measuring cylinder 4. A burette reads 2.50 cm3 at the start and 26.30 cm3 at the end. What volume was delivered? d. 23.80 cm3 Show answer
1 → a (Thermometer) · 2 → c (Measuring cylinder) · 3 → b (Pipette) · 4 → d (23.80 cm3)
- A thermometer measures temperature in °C.
- A measuring cylinder is graduated in cm3 for measuring volumes.
- A pipette delivers one exact volume; beakers are not accurate.
- Step 1. Volume = final − initial reading.
Step 2. 26.30 − 2.50 = 23.80 cm3.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
slightly too low · Crucible · In a fume cupboard · slightly too high- A student reads the top of the meniscus of water instead of the bottom. The reading will be .
- Which apparatus is used to heat a solid strongly to a high temperature? →
- Where should experiments that give off poisonous gases be done? →
Show answer
1: slightly too high · 2: Crucible · 3: In a fume cupboard
- Water curves upwards at the edges; the top of the curve is above the true level, so the reading is too high.
- A crucible is made of porcelain and resists very high temperatures.
- A fume cupboard removes harmful gases from the room.