Apparatus for Measurements
Section: 12. Experimental Techniques & Chemical Analysis | Syllabus: Cambridge IGCSE Chemistry (0620)
Apparatus for Measurement
Different pieces of apparatus are used to measure time, temperature, mass and volume, depending on how precise the measurement needs to be.
| Measurement | Apparatus | Notes |
|---|---|---|
| Time | Stop-watch | Reads to about ±0.01 s; human reaction time is the main source of error |
| Temperature | Thermometer | Bulb must be fully immersed and not touching the container |
| Mass | Balance | Zero (tare) the balance before use; never place chemicals directly on the pan |
| Volume | Measuring cylinder | Quick, approximate volume measurements |
| Volumetric (bulb) pipette | Fixed volume, measured accurately | |
| Burette | Variable, accurately-delivered volume - used in titrations | |
| Gas syringe | Measures the volume of a gas produced in a reaction |
Different apparatus have different advantages and disadvantages: a measuring cylinder is quick to use but only approximate, while a pipette or burette is slower to use but far more precise - the right apparatus depends on how accurate the experiment needs to be.
Reading the Meniscus
The meniscus is the curved upper surface of a liquid in a tube. Water and aqueous solutions form a concave meniscus (it curves downward in the middle).
- Always read at eye level - looking from above or below causes a parallax error
- For water and aqueous solutions, read the bottom of the meniscus
- A burette is numbered from 0 cm³ at the top downward, so readings increase down the burette
- Readings from a burette are recorded to 2 decimal places (e.g. 27.80 cm³); readings from a measuring cylinder are usually recorded to the nearest whole or half cm³
Worked Example
- Question (based on a real exam question): a burette's meniscus bottom sits between the 27 and 28 cm³ marks, closer to 28; a measuring cylinder's meniscus bottom sits above the 40 cm³ mark, about four-tenths of the way to 50 cm³. What are the two readings?
- Answer: burette = 27.80 cm³ (read to 2 decimal places, bottom of meniscus); measuring cylinder = 44 cm³ (bottom of meniscus, read to the nearest whole number).
Common Mistakes
- ❌ Reading a burette from above or below eye level
- ✓ this causes a parallax error - always position your eye level with the meniscus itself before reading
- ❌ Reading the top of the meniscus for an aqueous solution
- ✓ for water and aqueous solutions the meniscus curves downward, so the bottom of the curve is the correct reading point
Using a Pipette and a Burette
Pipette (delivers one fixed, accurate volume):
- Rinse the pipette with the solution to be measured (not water)
- Use a pipette filler - never pipette by mouth
- Fill above the calibration mark, then let liquid drain until the bottom of the meniscus sits exactly on the mark
- Let the liquid drain into the receiving vessel; touch the tip against the side and wait - do not blow out the drop left in the tip, as this is already accounted for in the calibration
Burette (delivers a variable, accurately-measured volume):
- Rinse the burette with the solution to be used, then fill it above the 0.00 cm³ mark using a funnel
- Remove the funnel, then open the tap briefly to fill the jet below the tap and remove any air bubble
- Record the initial reading, then add solution and record the final reading, both to 2 decimal places
- Volume delivered = final reading − initial reading
Interactive revision notes, videos and practice questions load below.