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I am conducting a titration to find the mass of aspirin present in tablets. I will be dissolving the aspirin tablet into a solution of ethanol and distilled water to dissolve it. But, does the volume of ethanol or distilled water added actually matter? Or does it just need to be enough to completely dissolve the aspirin?

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    $\begingroup$ You want to dissolve the tablet completely. However you don't want a huge excess of water. So 1.5 to 2 times the amount of the solvent mixture to dissolve the whole tablet. $\endgroup$ – MaxW Nov 21 at 17:20
  • $\begingroup$ @MaxW, all right, got it. Does the volume of solvent need to be precise, i.e. do I need to measure it using a pipette or will a measuring cylinder do? $\endgroup$ – Ali Nov 21 at 18:47
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    $\begingroup$ A graduated cylinder will certainly do. The notion is that you want to use about the same volume of solvent for each trial. $\endgroup$ – MaxW Nov 21 at 19:39
  • $\begingroup$ Concentration != mass. For concentration volume is crucial, for mass - not really. $\endgroup$ – Mithoron Nov 23 at 15:32
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At very great dilutions, impurities could have some effect on the end point. For example, even previously-distilled water will absorb some small amount of $\ce{CO2}$ from air, making it slightly more acid. However, if the aspirin is present in reasonable amount, that would have negligible effect. So, as stated by @MaxW, consistency, with a moderate theoretical excess of solvent, is important, but don't use greatly excessive amounts of solvent.

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