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Separations for SQA Higher Chemistry

Separations

This page covers the following topics:

1. Filtration
2. Distillation

Filtration is a technique used to separate a mixture of insoluble solids and a liquid. Filtration is possible due to the size differences of solid and liquid particles. Smaller liquid molecules can pass through a filter paper in a funnel to form filtrate, while larger solid particles cannot, forming residue. Dissolved ions are small enough to pass through the holes in the filter paper.

Filtrate is a filtered liquid which has passed through a filter paper. Residue is a solid which has been filtered out of a mixture and remains on the filter paper.

Filtration

Distillation is a technique which separates a mixture of liquids by their boiling point. This is a physical process as no chemical reaction is happening.

The mixture of liquids is placed in a round bottom flask and placed above a hot plate. A hot plate can be warmed up to a specific temperature, allowing more control than a Bunsen burner which is important when separating liquids with similar boiling points. As the mixture is heated, the liquid with the lowest boiling point will evaporate and travel up the glassware. A stopper placed at the top of the flask adapter prevents the gaseous samples from escaping and forces them through the condenser to be collected. When it reaches the cold environment of the condenser, the gas will condense and be collected as pure liquid. This is repeated until all the liquids are separated.

There are different forms of distillation such as simple distillation and fractional distillation. Fractional distillation is used for liquids with similar boiling points while simple distillation is used for liquids with relatively different boiling points. Fractional distillation is often used to separate a larger number of liquids than simple distillation, for example, crude oil.

Distillation

1

What is the purpose of a stopper in a distillation setup?

A stopper placed at the top of an adapter prevents gaseous samples from escaping and forces them through the condenser to be collected.

preventing gas from escaping

What is the purpose of a stopper in a distillation setup?

2

Suggest why a hot plate might be a better choice while heating a mixture during distillation than a Bunsen burner.

A hot plate can be warmed up to a specific temperature, allowing more control than a Bunsen burner which is important when separating liquids with similar boiling points.

Specific temperature setup on the Bunsen burner allows separating liquids with similar boiling points.

Suggest why a hot plate might be a better choice while heating a mixture during distillation than a Bunsen burner.

3

What is residue?

Residue is a solid which has been filtered out of a mixture and remains on the filter paper.

a solid left on a filter paper after filtration

What is residue?

4

When is fractional distillation used instead of simple distillation?

Fractional distillation is used for liquids with similar boiling points while simple distillation is used for liquids with relatively different boiling points. Fractional distillation is often used to separate a larger number of liquids than simple distillation.

for separating larger numbers of liquids with similar boiling points

When is fractional distillation used instead of simple distillation?

5

Name A, B and C in the diagram provided.

Filtration is a technique used to separate a mixture of insoluble solids and a liquid. Smaller liquid molecules can pass through a filter paper in a funnel to form filtrate, while larger solid particles cannot, forming residue.

A is funnel, B is mixture/residue, C is filtrate.

Name A, B and C in the diagram provided.

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