Laboratory Safety and Apparatus
Senior 1 · Chemistry
Laboratory Safety and Apparatus
Lesson 4 of 5
25 min
Pour 25 cm³ of water into a beaker using its printed markings, then pour it into a measuring cylinder. Does the cylinder read exactly 25 cm³? Usually it does not: the beaker's markings are only a rough guide. Chemists choose each piece of apparatus for its job: some only hold things, others measure them, and the measuring ones differ in how exactly they measure.
Figure 4.1: Apparatus for holding and containing, drawn as they appear in textbooks and exams.
Table 4.1: Apparatus for holding and containing
| Apparatus | Main use |
|---|---|
| Beaker | holding, mixing and warming liquids; its markings give rough volumes only |
| Conical flask | mixing and swirling liquids without spilling; the narrow neck slows evaporation |
| Round-bottom flask | heating liquids evenly, for example in distillation |
| Test tube | small-scale reactions and tests |
| Boiling tube | a wider, stronger tube for heating liquids and solids |
| Test-tube rack | holding test tubes upright |
| Test-tube holder | gripping a test tube while it is heated |
| Clamp stand (retort stand) | holding apparatus such as a burette or flask firmly in place |
| Spatula | scooping small amounts of a solid |
| Dropper (teat pipette) | adding a liquid a drop at a time |
| Wash bottle | squirting distilled water to rinse apparatus |
| Watch glass | holding a small amount of a solid, or covering a beaker |
Warning
Glassware safety. Check glassware for cracks and chips before you use it; a cracked beaker can break when heated. Never put hot glass on a cold, wet bench, because the sudden cooling can crack it. Tell your teacher about broken glass at once, and never pick it up with your fingers.
Volume in chemistry is measured in cubic centimetres () and cubic decimetres ():
Mass is measured in grams (g) on a balance, and temperature in degrees Celsius () with a thermometer.
Figure 4.2: Apparatus for measuring volume, temperature and mass.
Table 4.2: Measuring apparatus and how exactly each measures
| Apparatus | Measures | How exactly (typical school apparatus) |
|---|---|---|
| Beaker | rough volumes only | within about 5% |
| Measuring cylinder, 100 cm³ | any volume up to 100 cm³ | to the nearest 0.5 cm³ |
| Measuring cylinder, 10 cm³ | small volumes | to the nearest 0.1 cm³ |
| Pipette, 25 cm³ | one fixed volume, very exactly | 25.00 cm³, within about 0.06 cm³ |
| Burette, 50 cm³ | any volume that runs out of it, up to 50 cm³ | to the nearest 0.05 cm³ |
| Thermometer | temperature | to the nearest 0.5 °C or 1 °C |
| Electronic balance | mass | to the nearest 0.01 g |
Definition
Volume: the amount of space a substance takes up, measured in or .
Definition
Meniscus: the curved surface of a liquid in a narrow tube. For water and most solutions it curves downwards in the middle, and you read the bottom of the curve.
Definition
Parallax error: a reading error caused by looking at a scale from an angle instead of straight on. You avoid it by putting your eye level with the mark you are reading.
Figure 4.3: Reading volumes. Put your eye level with the bottom of the meniscus. On a burette the numbers increase downwards.
Worked example
Problem. In Figure 4.3 A, what is the volume of water in the measuring cylinder, and what would a student with the eye too high write?
Solution. Each small division is . The bottom of the meniscus is on the 36th line, so the volume is (half a division can be judged). Looking from above, the line of sight meets the scale above the meniscus, so the student would write a value that is too high, about .
Worked example
Problem. A burette reads before a titration and after it. What volume of solution was run out?
Solution. On a burette the numbers increase downwards, so the volume run out is the final reading minus the initial reading:
Answer: . Burette readings are always written to two decimal places, ending in 0 or 5.
Worked example
Problem. Choose the best apparatus for each job. (a) Put exactly 25 cm³ of acid into a flask. (b) Warm about 150 cm³ of water. (c) Measure out 45 cm³ of water to dissolve some salt. (d) Add an indicator one drop at a time.
Solution. (a) a 25 cm³ pipette: one fixed volume, very exactly; (b) a beaker: only a rough volume is needed; (c) a 50 cm³ measuring cylinder: good enough and quick; (d) a dropper.
Tip
Rinse a burette or pipette with a little of the solution it will hold, not with water. Water left inside would dilute the solution and spoil the measurement.
Warning
Never suck a liquid into a pipette with your mouth. Always use a pipette filler (a rubber bulb or pump). One mouthful of a corrosive or poisonous solution can cause serious harm.
Free Animated Education: Lab Tools and Equipment (5 min). As each item appears, find it in Figure 4.1 or 4.2.
Practice
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
