Practice Assignment 07
Method for preparing a titration reagent
It is probably easier for students to weigh into a weighing bottle rather than directly into a beaker, especially as it is such a small amount of sodium chloride.
The balance may be tared, but the procedure provides an opportunity for students to practise weighing by difference.
The amount has been chosen to give an approximately 0.025 mol dm-3 solution - similar to the concentration of silver nitrate used in PA 08 and SP 0008:2005: Determination of salt in butter. If time is available, students could therefore:
- use pre-standardised 0.025 mol dm-3 silver nitrate to check the accuracy of their sodium chloride solution
or: - use their standard sodium chloride solution to standardise an approximately 0.025 mol dm-3 solution of silver nitrate to use in PA 08.
Students should be made aware that a standard solution does not need to have a particular concentration, provided its actual concentration is accurately known. Thus, the mass of reagent weighed out can be anywhere within the given limits, provided its precise mass is measured, so its exact concentration can be calculated.
Health and safety note
Silver nitrate solution, if used for the extension task, stains skin and clothing.
Apparatus and Reagents
- Standard Procedure:
- SP 0007:2005 Method for preparing a titration reagent
- small bottle of sodium chloride
- distilled water
- 250 cm3 beaker
- 50 cm3 volumetric flask
- 50 cm3 measuring cylinder
- small funnel
- glass rod
- spatula
- small weighing bottle
- small dropper
- balance capable of weighing to 0.01g