AS Chemistry
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Can you tell me how to prepare a standard solution for titration, any example would do.
250509
Corrie writes ....
Let's say you wanted to make up a standard solution of sodium hydroxide, NaOH.
1. Work out the mass of 1 mole of NaOH. This is the mass you would have to dissolve to make 1 dm3 of a 1 mol dm-3 solution.
2. Depending on the concentration you want to make up, work out what mass of NaOH you will need to make 1 dm3 of solution. For example, to make 1 dm3 of a 0.2 mol dm-3 solution you would need only 0.2 mole of NaOH.
3. Now decide what volume of NaOH solution you need to make up. Let's say it is 500 cm3. This is 500/1000 dm3 = 0.5 dm3, so you will need only half of the mass of NaOH you worked out in 2.
4. I presume you know how to make up a standard solution, using a volumetric flask of suitable size. With a strong alkali such as NaOH some special precautions are are needed in handling the solid and the solution, and you need to work quickly when weighing as solid NaOH absorbs water from the air. You should not carry out such practical work without consulting your teacher/lab. supervisor and carrying out an appropriate risk assessment.
5. Note that some standard solutions are called primary standards. These are solutions that can be made up very accurately by weighing from substances that can be obtained in a very pure state, don't react with air or moisture when exposed to the atmosphere and whose solutions are stable. If other substances, such as NaOH solutions, are required for very accurate work, then they are usually made up in the normal way to an approximate concentration by weighing, but the solution is then titrated against a primary standard solution of accurately known concentration. The result is used to work out the accurate concnetration of the NaOH solution at the time of use - on standing it will absorb carbon dioxide from the air and change concentration.
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Risk assessment
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updated: 26 May 2009
