1. salicylic acid has the following solubility profile in water: 0.2 g/100 mL@ 2

Question

1. salicylic acid has the following solubility profile in water: 0.2 g/100 mL@ 20 0C and 7.5 g/100mL @ 100 0C; would water be a good solvent for a single-solvent recrystallization of salicylic acid (explain your reasoning)?

2. acetyl salicylic acid has the following solubility profile in ethanol: 18 g/100 mL@ 0 0C and 80 g/100mL @ 50 0C; would ethanol be a good solvent for a single-solvent recrystallization of acetylsalicylic acid (explain your reasoning)?

3. sucrose has the following solubility profile in water: 200 g/100 mL@ 25 0C and 260 g/100mL @ 80 0C; would water be a good solvent for a single-solvent recrystallization of sucrose (explain your reasoning)?  

Explanation / Answer

For a crystallization to work, a compound must not be too soluble at room temperature, but must become so with sufficient heating. Using the notion "like dissolves like" we'd expect compounds bearing a similar polarity to a solvent to readily dissolve in those solvents at room temperature - this therefore does not make a good solvent for crystallizations. On the flip side of this, if you have a very polar compound and say your solvent is absolutely nonpolar, we would expect that they might not mix even after considerable heating. Therefore, the idea is to find the solvent which shares some similarities w/ the solvent, but also some differences. That way the two can be coaxed to become soluble after heating. Take note of whether or not the molecule is polar. Is it a hydrocarbon - only hydrogen and carbon - and therefore nonpolar? Then take a look at the given solvents

so now,

1) Yes! you can use water for crystalization as its solubility is less at lower temperatures and one can easily decrease the temperature and crystalize the salycilic acid

2) yes u can use it for same reason but as acetyl salicylic acid is polar go for some more polar solvents if possible u will get less yield after crystallization here

3) No not useful because very less amount of sucrose will be crystallized and hecne not useful;

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