|
Mixtures
and separations
Francine
Taylor-Campbell, Contributor
 |
|
The prefect body, which ensures that discipline is maintained among their peers
at the Cedric Titus High School, located at Clark's Town in Trelawny. - Photo
by Noel Thompson | Syllabus
requirements Students
should be able to: - Identify
different types of solutions.
- Distinguish
among solutions, suspensions and colloids.
- Investigate
the effect of structure and temperature on the solubility of solids in water.
- Identify
suitable separation techniques based on differences in properties of the components
of a mixture.
Now,
let us look at a few questions 1.
Which of the following is the best method of obtaining pure water from ink? A.
chromatography
B.
distillation
C.
filtration
D.
freezing Answer
- B. Simple distillation is used to separate and purify a liquid from a non-volatile
solute. 2.
From which mixture can the underlined substances be obtained by adding water,
stirring and filtering? A.
calcium carbonate and sodium chloride
B.
copper (II) sulphate and sodium chloride
C.
ethanoic acid and ethanol
D.
iron and magnesium Answer
- A. Calcium carbonate is insoluble while sodium chloride is soluble in water.
Thus by adding water the insoluble portion is undissolved and can be removed by
filtering. Ethanoic acid is soluble in water, while magnesium and iron are both
insoluble, hence a different separating technique would be needed to separate
them. 3.
Ethanol and water can be separated by distillation because they have different
A. boiling
points
B.
densities
C.
nucleon (mass) numbers
D.
reactivities Answer
- A. Distillation is a technique used to separate liquids based on the differences
in their boiling points. An example of this is the separation of the components
of crude oil by fractional distillation. 4.
The table shows some information about the solubilities of three solids.
| Solid | 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 In
what order should the operations be carried out? A.
1 2 3 4
B.
3 1 2 (omit stage 4)
C.
3 4 1 2
D.
4 1 2 (omit stage 3)
E.
4 3 1 2 Answer
- D. Since L is the only substance soluble in water, it will dissolve leaving
J and M, which can be removed by filtering. To obtain pure L, the filtrate can
then be evaporated to dryness hence removing all the water. There is then no need
for step 3, which is the adding of ethanol. Please
continue to revise this topic by practising questions. Contributed
by Francine Taylor-Campbell. | 
