GCSE CHEMISTRY - Using Conductivity to find the End Point of a Titration - Titration of an Acid with an Alkali

Using Conductivity to find the End Point of a Titration.

At the start of this titration the conical flask contains a strong alkali that
is fully ionised in water. If electrodes are placed inside the conical flask
the ions in the water will conduct electricity and a current will flow.
Conductivity is a measure of how well the solution in the conical flask
conducts electricity. The more ions there are the better the conductivity and
the higher the current will be. The current can be measured using an ammeter.

As acid is added to the alkali
hydrogen ions and hydroxide ions react together to form water molecules.
The number of ions in the conical flask starts to decrease
and the current flowing through the solution will be seen to decrease.

At neutralisation all of the hydrogen ions and hydroxide ions have
reacted together to form water molecules. The neutral solution contains
only salt ions dissolved in water molecules. The solution will still conduct
electricity because of the salt ions but the current will be at a minimum.

As more acid is added the current will start to increase because there
will now be unreacted hydrogen ions in the solution as well as the
salt ions. The solution is now no longer neutral but has become acidic.
If you draw a graph of current against the amount of acid added
you can see where the minimum is. This is the end point of the titration
at neutralisation.

The End Point for Titration using Conductivity

The titration can be repeated
with the same amounts of acid and alkali used at the end point.
Pure salt crystals can then be crystallised from the neutral solution.

Headings Acids and Alkalis Search Questions

gcsescience.com Contents The Periodic Table Index Quizzes gcsescience.com