Volumetric analysis is a well established and versatile form of quantitative chemical analysis. The purpose of this type of analysis is to use an accurately known volume and concentration of one solution to find the accurate concentration of a second. The experimental procedure which allows us to do this is called a titration. This procedure is described in detail below.
Filling the burette
- Clean the burette, rinse it and dry the outside.
- Rinse it with the solution it is going to contain (acid).
- Fill the burette to above the 0ml mark.
- Check for air bubbles and invert to remove any, if required.
- Open the tap and run out some of the liquid until the tap connection is full of acid and no air remains (air bubbles would lead to an inaccurate result as they will probably dislodge during the titration).
- Remove the funnel (stops dripping while you read the meniscus).
- Release the liquid until the bottom of the meniscus is on the 0 ml.
Preparing the pipette
- Wash and rinse well.
- Rinse with the solution it is to contain.
- Suck up solution with a pipette filler, above the grad mark. Dry outside.
- Release the solution until the bottom of the meniscus is on the grad line.
- Tip off any hanging drop (this should not be counted).
- Allow to drain under gravity (do not blow).
- When drained touch the tip off the side, any drops which should be included will drain in. Leave the rest.
- If you are concerned about the accuracy of any pipettes you own, Pipette Calibration services are available online to make sure they are continuously accurate.
Preparing the conical flask
- Rinse several times with deionised water.
- Dry outside.
- Add base solution as described above, from the pipette.
- Rinse down walls of the flask with deionised water (you know exact volume added of base.)
Titration procedure
- Add indicator to the flask, 2 or 3 drops are enough because all indicators are weak acids or bases.
- Rinse down the sides with water.
- Run the solution into the flask from the burette, slowly.
- Rinse the sides of the flask regularly.
- Swirl the flask constantly, to ensure thorough mixing of reagents.
- As the end point nears, add the solution drop by drop.
- When the end-point is reached the indicator will change colour suddenly.
- At this point the acid will have exactly neutralised the base.
- Now read the meniscus of the burette, from the bottom, at eye level.
- Use a filter paper, if necessary, to make the meniscus more readable.
- Record your result.
- Repeat the titration several times.
- Get the average value.
- Only include the values that agree within 0.2ml of each other.