To determine the reacting volumes of a strong acid and a strong alkali by titration.
The titration method can be used to calculate the concentration of an acid.
- 25 cm3 volumetric pipette
- pipette filler
- 50 cm3 burette
- 250 cm3 conical flask
- small funnel
- 0.1 mol/dm3 sodium hydroxide solution
- sulfuric acid – concentration unknown
- phenolphthalein indicator.
- clamp stand, clamp & white tile
Diagram showing the apparatus needed to prepare a salt by titration
Make sure you remove the funnel after filling the burette as if left it can drop solution into the burette, leading to error.
- Use the pipette and pipette filler and place exactly 25 cm3 sodium hydroxide solution into the conical flask.
- Place the conical flask on a white tile so the tip of the burette is inside the flask.
- Add a few drops of a suitable indicator to the solution in the conical flask.
- Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm3 portions, while swirling the flask vigorously.
- Quickly close the tap when the end-point is reached (sharp colour change) and record the volume, placing your eye level with the meniscus.
- Now repeat the titration with a fresh batch of alkaline.
- As the rough end-point volume is approached, add solution from the burette one drop at a time until the indicator changes colour.
- Record the volume to the correct number of decimal places (to 0.1cm3).
- Repeat until you achieve two concordant results (two results that are within 0.1cm3 of each other) to increase accuracy.
Results: Record your results in a suitable table, e.g:
Concordant results should be achieved to calculate a mean titre.
The mean titre is calculated and used to calculate the concentration of the acid in mol/dm3, ignoring any anomalous results.
- The concentration of a solution can be expressed either in moles per dm3 or in grams per dm3.
- To go from g dm-3 to mol dm-3:
- Divide by the molar mass in grams.
- To go from mol dm-3 to g dm-3:
- Multiply by the molar mass in grams.
- Once a titration is completed and the average titre has been calculated, you can now proceed to calculate the unknown variable using the formula triangle as shown below.
- It can be used to derive equations for concentration and volume.
- From the triangle:
Concentration = moles ÷ volume
Volume = moles ÷ concentration
Formula triangle showing the relationship between concentration, number of moles and volume of liquid