Standardizing a Solution for Titration
Standardization is a crucial process in analytical chemistry, particularly in titrimetry. It involves determining the precise concentration of a solution, known as the standard solution, by reacting it with a known amount of a primary standard.
Why Standardize?
Titration relies on accurate concentration measurements. While solutions are prepared with a target concentration, slight variations during preparation can lead to inaccuracies. Standardization ensures the actual concentration is precisely known, leading to reliable titration results.
Choosing a Primary Standard
A primary standard must meet several criteria:
- High purity (99.9% or greater)
- Stable in air and under normal storage conditions
- Relatively high molar mass (to minimize weighing errors)
- Reacts completely and stoichiometrically with the analyte.
- Readily soluble in the solvent used for titration.
Procedure
The specific procedure varies depending on the standard solution and primary standard being used. However, general steps include:
- Accurately weigh a known mass of the primary standard.
- Dissolve the primary standard in a suitable solvent.
- Titrate the primary standard solution with the solution to be standardized using a suitable indicator.
- Record the volume of titrant used to reach the equivalence point.
- Calculate the concentration of the standardized solution using stoichiometry.
- Repeat the titration multiple times to ensure accuracy and precision. Calculate the average concentration and assess its standard deviation.
Example Calculation
Suppose you are standardizing a NaOH solution using potassium hydrogen phthalate (KHP) as a primary standard. You weigh 0.500 g of KHP (molar mass = 204.22 g/mol) and titrate it with NaOH. If 25.00 mL of NaOH solution are required to reach the equivalence point, the calculation of the NaOH concentration is as follows:
Moles of KHP = (0.500 g) / (204.22 g/mol) = 0.00245 mol
Since the stoichiometry of the reaction is 1:1 (one mole of KHP reacts with one mole of NaOH), moles of NaOH = 0.00245 mol
Concentration of NaOH = (0.00245 mol) / (0.02500 L) = 0.0980 M
Safety Precautions
Always wear appropriate safety goggles and gloves when handling chemicals. Dispose of chemicals properly according to your institution's guidelines.