Standard Solutions (Edexcel AS Chemistry): Revision Note

Core Practical 2: Preparing a Standard Solution

Volumetric Analysis

• Volumetric analysis is a process that uses the volume and concentration of one chemical reactant (a volumetric solution) 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

Some key pieces of apparatus used to prepare a volumetric solution and perform a simple titration 

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:

Steps 1 to 3:

1. Weigh out a precise amount of the solid.

2. Add it to a small volume of water in a beaker and stir with a glass rod to pre-dissolve the solid.

3. Transfer the solution to a volumetric flask through a funnel.

Steps 4 and 5:

4. Rinse the beaker (and rod and funnel) with distilled water and add the rinsings to the flask.

5. Make up to the scratch (graduation) mark with more water so the bottom of the meniscus sits on the mark, add the stopper and mix the contents.

Volumes & 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

  • parts per million