I am doing a lab on crystalization and on the prelab it asks theaffect of using more than the MINIMUM amount of solvent to dissolvethe solid (how the % recovery would be effected) and why thisoccurs.

I know the answer to the first part that if the % recovery will bereduced if more than the minimum amount of solvent is used todissolve the solid but I cannot find the reason for this. cananyone explain?

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Nestor RutherfordLv2

29 Sep 2019

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Hello, I am having trouble with these two Chemistry questions. We just completed a Separation of Mixtures lab with a mixture of sand and salt. We used the Filtration and Evaporation processes to remove the two components, I'm thinking that you could get a larger amount of sand if the sand residue was not dried enough, then this would cause the mass of the measured sand residue to be more, but I'm not sure if that is what they are asking for here.

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Fenbendazole is a weakly basic, hydrophobic drug used to treat cattle. The detection and determination of residual fenbendazole in milk and milk products is therefore important. Since milk and milk products cannot be injected directly into a chromatograph, various liquid-liquid extraction (LLE) procedures were investigated using spiked buffer solutions and milk samples. The table below shows the %recovery obtained when performing LLE on various samples at different pH values with either dichloromethane or ethyl acetate as the extracting organic solvent:

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pH	Buffer Milk	Buffer Milk
4.5	98 55	99 65
6.5	100 57	101 60
8.0	99 60	97 57
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(i) buffer at pH 8.0 and dichloromethane

(ii) milk and dichloromethane

(iii) buffer at pH 8.0 and ethyl acetate, and

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(d) In the final method, the fenbendazole extract was chromatographed on a reverse-phase C18 column using a mobile phase consisting of 50% acetonitrile and 50% 0.01 M phosphoric acid, with the addition of octanesulphonic acid (10 mM) to act as an ion-pairing reagent. What is an ion-pairing reagent, and why might it have been necessary for this sample?

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