You can add Acids and Alkalis together to Neutralise them. They react together and neutralise each other, forming a salt in the process. But you need to get the exact correct amount of each otherwise one will be neutralised, and the solution will become either Acidic or Alkaline.
We can measure the precise volumes of Acid and Alkali solutions needed to react with each other by a technique called titration. The point at which the Acid and Alkali have reacted completely is called the end point of the reaction. We show this by using a chemical called an indicator.
The pH of the solution left when an Acid and Alkali have completely reacted is not always 7. A neutral solution only forms when exactly the right amounts of a strong Acid react with a strong Alkali. If a strong Acid reacts completely with a weak Alkali, the solution formed at the end point is Acidic. And the reverse goes for if a Strong Alkali reacts with a weak Acid.
Indicators change colour over different pH ranges. So you have to choose a suitable indicator when carrying out Titrations with different combinations of Acids and Alkalis.
- Strong Acid + Strong Alkali = Any Indicator
- Weak Acid + Strong Alkali = Use Phenolphthalein
- Strong Acid + Strong Alkali = Use Methyl Orange
To carry out a Titration, you use this method:
- Measure a known volume of Alkali into a conical flask using a pipette
- Now add an indicator solution into the solution in the flask
- Put a solution of Acid you are going to use into a burette, so you can accurately measure the amount of Acid you need to neutralise the Alkali solution.
- Record the reading on the burette, then open the tap and release a small amount of acid into the flask. Swirl the flask to make sure the 2 solutions are mixed.
- Keep repeating the previous step until the indicator shows the Alkali solution has become fully reacted with the Acidic one. Read the recording on the burette to show how much Acid is needed to Neutralise the Alkali
- Repeat this at least 3 times to check your results. And then you can use your results to calculate how much of each solution is needed to neutralise the other.