Elements compounds and mixtures

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Slide 21

Mixtures

A mixture of lead atoms and chlorine atoms. They exist in no particular ratio and are not chemically combined with each other. They can be separated by physical means.

A mixture of PbCl2 and PbCl4 formula units. Again, they are in no particular ratio to each other and can be separated without chemical change.

منگل، 18 ذو القعد، 1436

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Slide 22

Characteristics of mixture

It is an impure substance

No formula

They can be mixed in any ratio.

The properties of the mixture are the properties of its constituents.

Constituents can be easily seperated by physical methods e.g. heating, drying, crystallization, distillation etc.

It is either homogenous or heterogenous.

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منگل، 18 ذو القعد، 1436

Slide 23

Difference between compounds & mixtures

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منگل، 18 ذو القعد، 1436

Slide 24

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منگل، 18 ذو القعد، 1436

Slide 25

Physical vs. Chemical Properties

Physical properties can be measure without changing the basic identity of the substance (e.g., color, density, odor, melting point)

Chemical properties describe how substances react or change to form different substances (e.g., hydrogen burns in oxygen)

Intensive physical properties do not depend on how much of the substance is present.

Examples: density, temperature, and melting point.

Extensive physical properties depend on the amount of substance present.

Examples: mass, volume, pressure.

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منگل، 18 ذو القعد، 1436

Slide 26

Physical and Chemical Changes

When a substance undergoes a physical change, its physical appearance changes.

Ice melts: a solid is converted into a liquid.

Physical changes do not result in a change of composition.

When a substance changes its composition, it undergoes a chemical change:

When pure hydrogen and pure oxygen react completely, they form pure water. In the flask containing water, there is no oxygen or hydrogen left over.

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منگل، 18 ذو القعد، 1436