A burette is filled with dilute hydrochloric acid and some of the acid is run into a conical flask containing 25.0 cm3 of aqueous sodium hydroxide. Fig. 3.1...

This tests reading a burette correctly and finding a titre. A burette is numbered from 0 at the top downwards and is graduated in 0.10 cm³ divisions, so it can be read to the nearest 0.05 cm³. On the scale shown the liquid surface sits below the 23 mark, a little under halfway to 24.

(a) [1] The reading in Fig. 3.1 is 23.45 cm³ [1] (accept 23.40 to 23.50; it must be given to two decimal places ending in 0 or 5, because the burette is read to the nearest 0.05 cm³).

(b) [1] The scale is read from the bottom of the meniscus, the lowest point of the curved liquid surface [1]. For a colourless solution this convention is always used so that everyone reads the same point.

(c) [2] Place your eye level with the bottom of the meniscus, looking horizontally at the scale [1]; this avoids a parallax error [1]. Looking from above or below the meniscus lines the mark up against the wrong part of the scale and gives a false reading.

(d) [1] The titre is the volume delivered, final minus initial reading:

\[ 23.45 - 1.20 = 22.25\,\mathrm{cm^3} \] [1]

(use your own answer to (a); correct subtraction earns the mark.)

(e) [1] A burette rather than a measuring cylinder is used because it is graduated in 0.10 cm³ divisions, so it reads to 0.05 cm³ and is far more precise, and it delivers the acid drop by drop so any volume can be measured and the end-point is not overshot [1].