Making a Volumetric Solution (AQA A Level Chemistry): Revision Note

Making a Volumetric Solution

Required Practical 1

Volumetric analysis

• Volumetric analysis is a process that uses the volume and concentration of one chemical reactant to determine the concentration of another unknown solution

• The technique most commonly used is a titration

• The volumes are measured using two precise pieces of equipment, a volumetric or graduated pipette and a burette

• Before the titration can be done, the standard solution must be prepared

• Specific apparatus must be used both when preparing the standard solution and when completing the titration, to ensure that volumes are measured precisely

Key:

1. Beaker

2. Burette

3. Volumetric pipette

4. Conical flask

5. Volumetric flask

Making a volumetric solution

• Chemists routinely prepare solutions needed for analysis, whose concentrations are known precisely

• These solutions are termed volumetric solutions or standard solutions

• They are made as accurately and precisely as possible using three-decimal-place balances and volumetric flasks to reduce the impact of measurement uncertainties

• The steps are:

• Step 1: Weigh the solid — either by difference (weigh bottle, tip into beaker, reweigh bottle) or by taring the beaker — on a balance reading to at least 2 decimal places

• Step 2: Dissolve in distilled or deionised water, stirring with a glass rod until all the solid has dissolved

• Step 3: Transfer to a volumetric (graduated) flask

• Step 4: Add the washings from the beaker and glass rod

• Step 5: Make up to the 250 cm³ mark with water, then stopper and invert to mix

Volumes and concentrations of solutions

• The concentration of a solution is the amount of solute dissolved in a solvent to make 1 dm³ of  solution

  • The solute is the substance that dissolves in a solvent to form a solution

  • The solvent is often water

• A concentrated solution is a solution that has a high concentration of solute

• A dilute solution is a solution with a low concentration of solute

• Concentration is usually expressed in one of three ways:

  • moles per unit volume

  • mass per unit volume

Related topics

• Performing a Titration & Volumetric Analysis

• Reacting volumes