Fig. 4.1 shows apparatus a student used to find the volume of dilute hydrochloric acid needed to neutralise aqueous sodium carbonate. Fig. 4.1 (a) Name the ...

This question checks that you can name standard titration apparatus and understand how a titration is run accurately. The tall graduated tube with a tap delivers a measured, variable volume of one solution into a flask containing the other solution and an indicator.

(a) Apparatus X (the long vertical graduated tube) is a burette [1]; it measures the variable volume of acid added.

(b) Part Y at the bottom of the burette is the tap / stopcock [1]; it controls the flow of acid, allowing drop-by-drop addition near the end-point.

(c) Apparatus Z (the container the acid runs into) is the conical flask [1]; its shape lets the contents be swirled without splashing out.

(d) A suitable indicator for a strong-acid / strong-base titration is methyl orange [1] (screened methyl orange or thymolphthalein is also accepted); it gives a sharp, single colour change at the end-point.

(e) A sensible safety precaution is to wear eye protection / safety goggles [1] (accept: wipe up spills, keep the acid off the skin), because the acid and alkali are irritant or corrosive.

(f) The flask is swirled to mix the acid and alkali thoroughly and evenly, so the reaction is complete throughout and the indicator colour change is seen accurately at the true end-point [1]. Without swirling, unreacted alkali near the walls delays the colour change and gives a titre that is too large.