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14 Cards in this Set

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Meaning of Mixture

Mixture is made up of two or more substance that are not chemically combined

Meaning of pure substance

Made up of single element or compound. It is not mixed with any other substance

Effects of impurities on melting point?

Lower the melting point of a solid. The greater the amount of impurities, the lower the melting point.


Causes melting point to take over a range of temperatures. e.g. benzoic acid may melt over a temperature range of 118-121*C

Method of separation

Filtration


Evaporation to dryness


crystallisation


using a suitable solvent


simple distillation


Fractional distillation

When to use Filtration

Separating an insoluble solid from a liquid




separate insoluble solid particles from a liquid




the solid left on the filtrate paper is called residue




The liquid that passed through the filtrate paper is called the filtrate

when to use Evaporation to dryness

separating a soluble solid from a liquid




obtain a soluble solid from a solution by heating it until the water has boiled off

when to use Crystallisation

separating a soluble solid from a liquid


solid decompose upon strong heating




Obtain a pure solid sample from its solution




When heating, it does not heat till it boils




E.g. Sugar decompose to water and carbon when heated strongly.

When to use a suitable solvent method

solvent meaning: the remains of a solution after separation is a solvent




Separating a soluble solid from an insoluble solid

when to use Simple distillation

Used to separate a pure solvent from a solution




2 things to remember in the diagram:


Thermometer and condenser

Procedure to note:

Thermometer:


The bulb of the thermometer should be placed beside the side arm of the distillation flask. it should not be dipped into the solution.




Reason


ensures that the thermometer measures the boiling of the substance that is being distilled




Condenser:


1)The condenser should be sloped downwards. The condenser consist of 2 tubes: an inner tube and outer water jacket




2)Cold running water is allowed to enter the water jacket from the bottom of the condenser and leaves at the top.




Reason


1)Ensure that the pure solvent formed runs downwards into the receiver (conical flask)




2) if water enters from the top of the condenser, it will exit the condenser before the water jack can be completely filled. Thus it must enter from the bottom to keep the jacket always completely filled. Also a more efficient way of cooling.

when to use fractional distillation

Used to separate a mixture of miscible liquid.




2 things to remember in the diagram:


glass beads and fractionating column

Fractionating column and glass beads

When the 2 liquid vapour rise up, the one with higher boiling point condense along the fractionating column and fall back into the round-bottomed flask.

When to use Choromatography

Separating two or more components that dissolve in the same solvent




used to test from banned substance present in food colouring

How to identify a banned substance present in food colouring?

1.Paper chromatography is used to separate the dyes in the sample.


2. Each dye is identified by comparing its position in the chromatogram with that of a known dye on the same chromatogram


3. Chemist can then check against a database of banned dye to see if the dyes are permitted for use in food