Seperating Mixtures

Question 1

Filtration

Answer 1

The technique of filtration is used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent. For example you have tried to separate a mixture of sand and salt.

The sand that you collect on the filter paper can then be washed with distilled water to remove any salt solution left on it. The wet sand is finally dried in a warm oven to evaporate any water off and leave the pure dry sand.

Question 2

Crystiallisation

Answer 2

Crystallisation is a separation technique that is used to separate
a solid that has dissolved in a liquid and made a solution.

The solution is warmed in an open container,
allowing the solvent to evaporate, leaving a saturated solution.
A solution that has as much solid dissolved in it
as it can possibly contain is called a saturated solution.

As the saturated solution is allowed to cool,
the solid will come out of the solution and crystals will start to grow.
The crystals can then be collected and allowed to dry.

A solid that does not dissolve in
a liquid can be separated by filtration.

The size of crystals depends on the rate of cooling.
Fast cooling will result in a large number of small crystals.
Slow cooling will result in a smaller number of large crystals.
See for example basalt and granite rock formations.

Question 3

Distillation

Answer 3

A solution is heated and boiled to evaporate the solvent. The vapour given off then enters a condenser. This acts as a cooling jacket around the inner tube from the flask. Here the hot vapour is cooled and condensed back into a liquid for collection in a flask. Any dissolve d solids will remain in the heated flask.

Question 4

Solute

.

Answer 4

The Substances which dissolve in solvent

Question 5

Solvent

Answer 5

The liquid in which a solute is dissolved to form a solution.

Question 6

Solution

Answer 6

It is a homogenous mixture (a mixure in which no more solute can be dissolve) of two or more components.

Question 7

Fractional distilstion

Answer 7

Fractional distillation differs from distillation only in that it separates a mixture into a number of different parts, called fractions. A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Like distillation, fractional distillation works because the different substances in the mixture have different boiling points.

Question 8

Chromatography with paper

Answer 8

Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, eg water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.

Question 9

What are Rf values

Answer 9

Different chromatograms and the separated components of the mixtures can be identified by calculating the Rf value using the equation:
Rf = distance moved by the compound ÷ distance moved by the solvent
The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way. This allows industry to use chromatography to identify compounds in mixtures.

Question 10

Name 4 types of separation

These techniques all rely on differences in the physical properties of the substance or mixture for example different solubilities in a solvent or different boiling points

Answer 10

• filtration
• crystallisation
• distillation
• chromatography