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Choosing and using measuring apparatus

Edexcel IAL Chemistry · WCH13 Practical Skills in Chemistry I

Many marks in Unit 3 come from choosing the right piece of apparatus and using it properly. The choice depends on how precisely the quantity has to be known.

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Which apparatus for which job

Apparatus	Use	Typical resolution or uncertainty
volumetric (bulb) pipette, 25.0 cm³	an accurately known fixed volume of solution	about ±0.06 cm³
burette, 50 cm³	variable volumes added accurately (titres, or a volume such as 7.50 cm³)	read to 0.05 cm³; ±0.05 cm³ per reading
volumetric flask, 250.0 cm³	making a standard solution of accurately known concentration	the mark gives one exact volume
measuring cylinder	approximate volumes, such as an acid that is in excess	about ±0.5 cm³ for a 100 cm³ cylinder
gas syringe, 100 cm³	volume of gas produced	usually read to 1 cm³
balance	mass	2 or 3 decimal places (0.01 g or 0.001 g)
thermometer	temperature	0.1 °C (digital) to 1 °C (some glass ones)

Values follow Pearson's practical guide; a question will give the uncertainty if it matters.

Range and resolution

Resolution is the smallest change the instrument can show. A balance reading to 0.01 g has a resolution of 0.01 g.
Range is the span it can measure. Choose an instrument whose range covers the expected value: a 50 cm³ syringe cannot hold 80 cm³ of gas.
Use precise apparatus only where precision matters. If a reagent is in excess, a measuring cylinder is fine, because its exact amount does not affect the result.
A pipette delivers only its fixed volume, so a volume such as 7.50 cm³ needs a burette (a common error in the October 2024 paper).

Using them properly

Pipette: use a pipette filler; rinse with the solution it will deliver; fill so the bottom of the meniscus sits on the mark at eye level; let it drain and touch the tip on the surface.
Burette: rinse with the solution it will hold; fill with a funnel, then remove the funnel; fill the tip below the tap; read the bottom of the meniscus at eye level.
Volumetric flask: add the last drops of water with a dropping pipette so the meniscus sits on the mark; stopper and invert to mix.
Weighing by difference: weigh the container with the solid, tip the solid out, reweigh the container. The difference is the mass actually transferred, even if some solid sticks.

Worked example

Choose apparatus for each: (a) 25.0 cm³ of sodium hydroxide for a titration; (b) 20 cm³ of dilute sulfuric acid in excess; (c) about 80 cm³ of hydrogen gas; (d) 12.40 cm³ of potassium iodide solution.

(a) A fixed, accurately known volume: 25.0 cm³ volumetric pipette.
(b) In excess, so precision is not needed: measuring cylinder.
(c) Gas of about 80 cm³: 100 cm³ gas syringe.
(d) A variable volume known to 0.05 cm³: burette.

Answer: pipette; measuring cylinder; 100 cm³ gas syringe; burette

Key idea: Pipette for fixed accurate volumes, burette for variable accurate volumes, volumetric flask for standard solutions, measuring cylinder only where precision does not matter. Check range and resolution, and weigh by difference.

Check yourself

Which apparatus should be used to add exactly 7.50 cm³ of a solution to a reaction mixture?
- A 10 cm³ measuring cylinder
- A 25.0 cm³ pipette
- A beaker with volume markings
- A burette
Show answer
A burette. A burette delivers variable volumes to 0.05 cm³. Pipettes give only their fixed volume.
Dilute sulfuric acid is added in excess before a titration. Why is a measuring cylinder acceptable for it?
- Sulfuric acid damages pipettes
- Its exact amount does not affect the result, because it is in excess
- Measuring cylinders are more accurate than pipettes
- The acid is the solution being titrated
Show answer
Its exact amount does not affect the result, because it is in excess. Only the limiting quantities must be known precisely.
About 85 cm³ of gas is expected. Which piece of apparatus is best?
- A 50 cm³ gas syringe
- A 10 cm³ measuring cylinder
- A 25.0 cm³ pipette
- A 100 cm³ gas syringe
Show answer
A 100 cm³ gas syringe. The range must cover the expected volume.
What should a pipette be rinsed with just before it is used?
- The solution it is going to deliver
- Distilled water
- Ethanol
- The solution in the burette
Show answer
The solution it is going to deliver. Water left inside would dilute the solution and lower the moles delivered.
A balance shows 12.37 g. What is its resolution, in g?
Show answer
0.01 g. It reads to two decimal places, so the smallest change it shows is 0.01 g.
Why is a solid 'weighed by difference' when making a standard solution?
- The mass found is what actually left the container, even if some solid stays behind
- It makes the balance more precise
- It removes the need to use a volumetric flask
- It stops the solid absorbing water
Show answer
The mass found is what actually left the container, even if some solid stays behind. Reweighing the container accounts for any solid that sticks to it.
Explain why the funnel should be removed from the top of a burette before the initial reading is taken.
Show answer
Drops of solution left in the funnel could fall into the burette and change the reading.. Liquid draining from the funnel would make the initial reading wrong.

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Last updated 8 November 2026. Spotted a mistake? Tell us.