Cheee

TOPIC: SEPARATION TECHNIQUES (ANSWERS)

1. The table below shows some information about the solubilities of three substances.
|Substances             |Solubility in water           |Solubility in ethanol           |
|J                     |Insoluble                     |Soluble                         |
|L                     |Soluble                       |Insoluble                       |
|M                     |Insoluble                     |Insoluble                       |

    The following operations could be carried out to obtain pure L from a mixture of J, L and M.
    1. filter
    2. evaporate filtrate to dryness
    3. add ethanol
    4. add water
    What order should the operation be carried out?
    A 1, 2, 3, 4 C 3, 4, 1, 2
    B 3, 1, 2 (Omit stage 4) D 4, 1, 2 (Omit stage 3) [ D ]

    (Comments:
    1st step is to add water so that only L dissolves while J and M remain insoluble. By filtering, J and M will be the residue while L is in the filtrate. There is no need to separate J and M as question says “to obtain pure L”, hence the objective of the experiment is to obtain pure L and not the other two. Last step is to evaporate filtrate to dryness to recover L in solid form)

2. A sample of iodine crystals is contaminated by some sodium chloride crystals. Which of the methods will best separate iodine crystals from the impurities?
A Dissolve in water and filter
B Dissolve in alcohol and filter
C By sublimation
D By chromatography [ C ]

(Comments:
    Recall that iodine can sublime i.e. change directly from solid into gaseous state without going through the liquid state while sodium chloride cannot. Hence the easiest way is to sublime the mixture.)

3. Chromatography Fractional distillation Filtration
Evaporation to dryness Using separating funnel Distillation
Crystallisation Dissolution then filtration

Select from the above list, the methods for separating
a. two miscible organic...