General Laboratory Techniques

Standard Solution Preparation

A standard solution is a solution with a precisely known concentration. It is often used in titrations to determine the concentration of other solutions.

Steps to Prepare a Standard Solution

1. Weigh the Solute: Accurately weigh the required amount of solute using a balance.
2. Dissolve the Solute: Transfer the solute into a volumetric flask and add distilled water to dissolve it completely.
3. Fill to the Mark: Add distilled water up to the calibration mark on the flask to achieve the desired volume.
4. Mix Thoroughly: Invert the flask several times to ensure the solution is homogeneous.

Recrystallisation

Recrystallisation is a technique used to purify solid compounds. It involves dissolving the impure solid in a solvent and then allowing it to slowly crystallize out.

Steps for Recrystallisation

1. Dissolve the Impure Solid: Heat the solvent and dissolve the impure solid in it.
2. Filter the Solution: Use a filter to remove insoluble impurities.
3. Cool the Solution: Allow the solution to cool slowly so that pure crystals form.
4. Collect the Crystals: Use filtration to collect the crystals and wash them with cold solvent.
5. Dry the Crystals: Allow the crystals to dry completely.

pH Measurement

The pH of a solution indicates its acidity or alkalinity. It is measured on a scale from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is alkaline.

Methods of Measuring pH

• pH Meter: An electronic device that gives a digital reading of pH.
• pH Paper: Paper strips that change color according to the pH of the solution.
• Indicators: Chemicals that change color at specific pH levels.