- Standard solution: A solution with an accurately known concentration.
- Primary standard solution: A solution prepared from a solid that:
- Is water-soluble.
- Has a high purity.
- Has a known formula.
- Is stable in air.
- A primary standard solution can be prepared using the following procedure:
- Determine the mass of primary standard required to form the desired primary standard solution concentration.
- Weigh the required amount of primary standard into a beaker.
- Dissolve the primary standard in a small amount of water.
- Transfer all of the solution from the beaker to a volumetric flask, washing residue into the flask using distilled water.
- Add distilled water to the volumetric flask until the meniscus of the water is level with the calibration mark.
- Titration: A volumetric analytical technique used to determine the concentration of a solution by reacting it with a standard solution.
- Secondary standard solution: A solution that has had its concentration determined by a titration with a primary standard solution.
- The end-point of a titration is indicated by a change in colour of an indicator solution.
- An indicator is selected that changes colour at the pH of the salt solution formed at point of neutralisation (equivalence point):
|Type of titration||Equivalence point||Suitable indicator(s)|
|Strong acid and strong base||Neutral||Bromothymol blue or litmus|
|Strong acid and weak base||Acidic||Methyl orange|
|Weak acid and strong base||Basic||Phenolphthalein|
- Titration procedures involve several pieces of volumetric glassware:
- Pipette: A volumetric glassware item used to transfer a known volume of a solution into a conical flask.
- Burette: A volumetric glassware item used to transfer one solution into another at a controlled rate.
- All glassware used in titration procedures needs to be washed thoroughly before use, first with normal water, then with distilled water.
- A titration of a strong basic standard solution and a weak acidic solution of unknown concentration can be performed using the following procedure:
- Add a known volume of the acidic solution into a conical flask using a pipette.
- Add a few drops of phenolphthalein indicator to the conical flask.
- Fill a burette with the basic solution to the highest calibration mark.
- Use the burette to add the basic solution to the acidic solution until the equivalence point is reached, indicated by a change in indicator colour from colourless to red.
- Record the volume of acidic solution used to reach the equivalence point.
- Repeat the above procedure several times, slowing the transfer rate from the burette when the previously transferred volume is neared.
- Using the concentration of the basic solution, the volumes of both solutions, and the equation of the neutralisation reaction, determine the concentration of the acidic solution.