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Drawing and labelling apparatus

Edexcel IAL Chemistry · WCH13 Practical Skills in Chemistry I

Unit 3 often asks you to draw a set-up. Examiners look for a working arrangement: correct pieces, correct connections, no gaps, nothing dangerously sealed and clear labels.

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Rules for any diagram

Draw a simple 2D cross-section and label every piece.
Pieces that are separate (flask, still head, condenser) should look separate where they join; do not draw the set-up as one continuous outline.
No gaps where vapour or gas could escape.
Never seal apparatus that is being heated: pressure would build up. A bung with no outlet is a common error.
Show water in at the bottom of a condenser and out at the top.
Show the heat source (electric heater or water bath for flammable organics).

Reflux and distillation

Reflux: round-bottomed flask with anti-bumping granules, condenser vertical and open at the top. Vapour condenses and runs back, so you can heat for a long time without losing volatile substances.
Distillation: flask, still head with the thermometer bulb level with the side arm (it reads the temperature of vapour leaving), condenser sloping downwards, and a receiver (in ice for a volatile product). The receiver is open to the air, not sealed.
Fractional distillation: a fractionating column between flask and still head; its top is closed by the still head, not left open.

Separation and gas collection

Separating funnel: a pear-shaped funnel with a stopper and a tap, narrow at the bottom. Run off the lower layer through the tap.
Filtration under reduced pressure: a Buchner (or Hirsch) funnel with a perforated plate, filter paper flat on the plate, a bung into a side-arm (Buchner) flask joined to a vacuum pump. The funnel and flask are separate pieces.
Gas collection: delivery tube to a gas syringe, or to an inverted measuring cylinder full of water in a trough (not for very soluble gases).

Worked example

A student's distillation diagram has these faults. Say how to correct each: (1) water enters the condenser at the top; (2) the thermometer bulb is in the liquid; (3) the receiver is a stoppered flask; (4) a gap between the still head and condenser.

(1) Water in at the bottom, out at the top, so the condenser jacket stays full.
(2) Bulb level with the side arm, to read the temperature of the vapour being collected.
(3) Open receiver (or one with a vent), so pressure cannot build up.
(4) Draw the joint closed, so vapour cannot escape.

Answer: Reverse the water, raise the bulb to the side arm, leave the receiver open and close the gap.

Key idea: Labelled, connected, no gaps, never sealed when heated, water in at the bottom. Reflux: vertical open condenser. Distillation: bulb at the side arm. Buchner: perforated plate and side-arm flask.

Check yourself

Where should the thermometer bulb be placed in a distillation apparatus?
- Level with the side arm of the still head
- In the boiling liquid
- At the bottom of the condenser
- In the receiving flask
Show answer
Level with the side arm of the still head. It must measure the temperature of the vapour that is passing into the condenser.
Why does cooling water enter a condenser at the bottom?
- So the water flows faster
- To stop the glass cracking
- So the outer jacket fills completely and cools efficiently
- So that the vapour is heated
Show answer
So the outer jacket fills completely and cools efficiently. Entering at the top would leave air pockets and poor cooling.
Why must a heated reflux apparatus not be sealed at the top?
- Pressure would build up and the apparatus could burst
- The condenser would stop working
- Air is needed for the reaction
- The thermometer would break
Show answer
Pressure would build up and the apparatus could burst. Heating a closed system raises the pressure.
Which feature is often missed in drawings of filtration under reduced pressure?
- The thermometer
- The condenser
- The anti-bumping granules
- The perforated plate in the funnel, with the filter paper on it
Show answer
The perforated plate in the funnel, with the filter paper on it. The examiners' report noted the perforated base was often missing or drawn above the paper.
What is the purpose of heating under reflux?
- To separate liquids by boiling point
- To heat a mixture for a long time without losing volatile reactants or products
- To remove water from a product
- To collect a gas
Show answer
To heat a mixture for a long time without losing volatile reactants or products. The vertical condenser returns vapour to the flask.
Why are anti-bumping granules added before heating?
- To speed up the reaction as a catalyst
- To dry the liquid
- To raise the boiling point
- To give smooth boiling and stop violent bumping
Show answer
To give smooth boiling and stop violent bumping. They provide sites for small bubbles to form.
Explain why a water bath or electric heater, rather than a Bunsen burner, is used to heat ethanol under reflux.
Show answer
Ethanol is flammable, so a naked flame must be avoided.. Organic vapours can ignite in a Bunsen flame.

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