Topic 15 safety note

Please read this safety note if you have not already seen it.

To all those teaching Nuffield Advanced Chemistry

Safety note about Experiment 15.3 part 1: 'Hydrolysis of an ester'

We were contacted by CLEAPSS about an accident which took place while a student was carrying out the hydrolysis of an ester described in the first part of Experiment 15.3.

Twenty minutes into the refluxing, the hot alkali shot out of the top of the reflux condenser. Fortunately the student was wearing eye protection and there was no injury. Anti-bumping granules were being used. The cause of this could be one or all of the following:

• a lack of attention by the student during the reflux,
• the pear-shaped flask being too full of liquid,
• secondary refluxing in the neck of the flask,
• use of a too powerful flame instead of a flame adjusted so that boiling just occurs.

CLEAPSS advise us that this experiment should proceed with the 2 cm³ of methyl benzoate and only 15 cm³ of 2M sodium hydroxide solution. So we recommend that you amend Experiment 15.3 on page 367 of the Students’ book to specify 15 cm³ rather than 30 cm³ of the sodium hydroxide solution. It would also be a good idea to add a note, as a reminder, to your copies of the Teachers’ guide.

When students carry out this experiment, CLEAPSS recommends that you check the apparatus before refluxing begins and keep a close eye on the procedure being followed by the students while bearing in mind the factors which might lead to hazardous ‘bumping’.

Andrew Hunt

Whilst every care has been taken in the preparation of this note, and information in it is believed to be correct and based upon the best advice currently available, no guarantee can be given as to its accuracy, and no liability is accepted for any loss, damage, or injury arising from the use of the information.