Chemistry Competition

Professional analysts often use `proficiency tests' to assess their work. This competition is a version of a proficiency test. The stages of a proficiency test are:

• Identical samples are sent to a group of laboratories
• The laboratories send their results back. The organisers use statistical methods to evaluate them.
• A confidential report is sent to the participants. The laboratories are not identified by name. The results are coded so that the participants can recognise their own results and see how well they have done.
• The results can reveal a surprising lack of agreement between the experts but the schemes are friendly affairs. If a laboratory has difficulties it can often seek advice from the scheme organiser who will be widely experienced in the tests concerned.
• After a few rounds of tests the quality of the data tends to improve.

In the competition each team of students is treated as a separate laboratory. Every group participating in the competition receives a vial containing a solution of ethanoic acid. In each school or college the vials are coded and have a slightly different concentration.

The task is to find the concentration of the acid. To do this the students have to:

• prepare clean glassware,
• standardise a solution of sodium hydroxide,
• dilute the ethanoic acid sample quantitatively,
• titrate the diluted acid with the sodium hydroxide,
• calculate the concentration of the undiluted acid from their results,
• identify and comment on sources of error.

The students results are sent to LGC where statisticians analyse and compare the performance of the teams by computing a `Z score'. A `Z score' represents the closeness of an individual result to an agreed value.

Schools taking part in the competition are supplied with all the information they need.

The LGC has now published a training pack consisting of a Guide to Improving Analytical Quality in Chemistry and a Basic Laboratory Skills CD-ROM.

The pack has been developed for year 12 and 13 pupils (A-level and GNVQ) but may also be useful for first year students at University.

The purpose of the guide is to pass on some of the knowledge that an experienced analyst will usually learn over a period of years. It is not intended to cover every aspect of chemical analysis but to show how common pitfalls can be avoided and this should produce improved results.

The CD-ROM requires 486 processor or faster running Windows 95.