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Preparation of standard solution: HELP!

Q: Why is a standard solution not made by dissolving a known mass of primary standard substance in a known volume of solvent?

Problem: I swear that IS how you make a standard solution? E.g. Dissolving a known mass of sodium carbonate into a known volume of distilled water gives you a standard solution, no? Please can someone explain to me where I'm wrong :frown:

Reply 1

Asklepios

Original post by thnkhppythghts

I would agree with you, but MAYBE this is what they want?

A standard solution is of a specific concentration right? So either you dissolve a known mass of solute into a calculated volume of solvent or a calculated mass of solute into a known volume of solvent.

Hope that makes sense

Reply 2

Inserve Writers

I think you should use a known weight rather than mass. In the end, the concentration should be in grams per volume

which relates to weight.

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Reply 3

thnkhppythghts

Thanks for everyone that replied. Turns out that the correct answer was:

A standard solution is made by dissolving a known mass of sodium carbonate in distilled water building up to a known volume. For example, you cannot add 50grams of sodium carbonate to 250ml of distilled water because 1) needs to dissolve completely and 2) trace sodium carbonate would be left behind and this needs to be transferred to the beaker by washing it with distilled water and transferring the washings to the beaker to ensure all of the sodium carbonate has been used until you reach the 250ml mark. By transferring the washings, you are altering the overall volume if you started out with 250ml already.