Standard solutions

'Preparing a Primary Standard Solution'

A primary standard is one that:

• Is available in a highly pure state.
• Is stable in air.
• Is readiily soluble in water.
• Has a high relative formula mass.
• Will react rapidly when in solution during volumetric analysis.

The recipe:

1. Work out how much you want (volume) and select the appropriate glassware!
2. Wash out the glassware carefully.
3. Work out how much solid you require.
4. Weigh a clean and empty weighing bottle.
5. Weigh out your solid using a clean spatula on a balance which will weight to 0.01g.
6. Transfer the solid from your weighing bottle into a clean beaker.
7. Either wash out any remaining solids into the beaker, using distilled water, or re-weigh the weighing bottle and adjust the mass used in your laboratory book for the solid that was not transferred.
8. Use a glass stirring rod to gently break up any crystals to a smaller size.
9. Dissolve the solid in a mixture of about 80% of your final required volume.
10. Decant the liquid into a volumetric flask.
11. Rinse out the beaker with a little more solvent and add the washings to the flask (REPEAT).
12. Top up the volume with distilled water from a dropping pipette until the bottom of the meniscus is level with the graduation.
13. Place the stopper in the volumetric and invert several times to ensure complete mixing and a homogeneous solution.
14. Calculate the molarity (concentration) of the solution.
15. Transfer your solution to a clean bottle.
16. Label the solution with your name, date, name of solution and molarity.