Anticipating practical difficulties

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Tackling a practical titration for the first time can be extremely challenging for the students, and for the teacher.  Consider the following problems, and how you might pre-empt them.

Reading the graduated scale of a burette. The scale appears opposite to the familiar reading of measuring cylinder scales.

An initial practical session with burettes could include nothing more chemical than water itself. Water is sufficient for practising handling, filling and reading a burette. Students taking their first readings might initially give some surprising numbers, so make sure they get lots of practice.

Putting together the many steps involved in setting up and performing a successful titration.

Try a 'buddy system' where one student runs the titration and the 'buddy' gives a running commentary of all the steps. This can include good points ('You've remembered to take the funnel from the burette') and pointing out errors ('Oh dear, you've waggled the pipette and blown the very last drop out').

Understanding the many steps carried out practically in a titration.

Using the 'buddy system', students could explain to their partner the reasons why they are doing each step. They may know how to carry out 'good practice' in their technique, but can they explain why? For example, why is the burette lowered to fill it? Why is it necessary to check for air bubbles and get rid of them before titrating? Why should the inside of the flask be rinsed down with a little distilled water as the end point is approached?

Choosing a suitable indicator can be a problem.

This is considered in detail later, in the topic Indicators.

 
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