Compound A is recrystallized from n-propanol. Given are the following solubilities (in 100 mL of solvent): 160 g/100 °C, 100 g/80 °C, 60 g/60 °C, 20 g/20 °C, 15 g/10 °C and 10 g/0 °C. How many milliliters of solvent are needed to dissolve 80.0 g of compound A during the recrystallization?
800 mL
134 mL
400 mL
50 mL
80 mL
At what temperature do you wish to start? That will be dictated partially by the melting point of compound A as well as the boiling point of n-propanol. For example, (but you don't want to use this one), if we use the 100 C data,
100 mL x (80/160) = 50 mL. However, you don't want to use this one because n-propanol boils < 100 C. In fact, if you will look at the data, every possible answer is there using the formula,
100 mL x (80/table value) = ??
Therefore,
100 mL x 80/160 = 50 mL
100 mL x 80/100 = 80
100 mL x 80/60 = 133
100 mL x 80/20 = 400
etc.
Look at your notes and in the lab preparation material, as well as the melting point of compound A to make your choice.