O-Level Experimental Chemistry: worked solution

Question

For each task below, name the most appropriate piece of apparatus. (a) collecting 15.6 cm3 of carbon dioxide from a reaction (b) finding the boiling point of a solution (c) delivering 22.3 cm3 of sodium hydroxide (d) timing how fast salt dissolves in water (e) measuring out roughly 20 cm3 of a liquid

For each task ask two questions: what quantity is being measured, and how accurately does it have to be measured? (a) collecting 15.6 cm3 of carbon dioxide from a reaction - gas syringe. A volume of gas is wanted, quoted to 0.1 cm3, so it must be measured as it is collected. The gas pushes the plunger out and the volume is read straight off the barrel scale. Collecting over water would lose some of it, because carbon dioxide dissolves in water. (b) finding the boiling point of a solution - thermometer. A boiling point is a temperature. The bulb is held in the vapour just above the boiling liquid and the reading is taken when it stops rising. (c) delivering 22.3 cm3 of sodium hydroxide - burette. A burette runs out a variable volume that is known accurately: read the level before and after and subtract. A pipette can only deliver one fixed volume (25.0 cm3), so it cannot give 22.3 cm3. (d) timing how fast salt dissolves in water - stopwatch. The quantity measured is time, from the moment the salt is added to the moment the last crystal disappears. (e) measuring out roughly 20 cm3 of a liquid - measuring cylinder. 'Roughly' means high accuracy is not needed, so the quick scale of a measuring cylinder is enough (read to the bottom of the meniscus at eye level).