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Roshan kumar


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A compound is substance made up of constant continuous composition...

Wat does this mean??


Good question because although the above quote is a true statement it is a pretty poor definition at best and misleading at worst.


So I suggest we should start by considering what a substance is.


Objects can be material objects, like spoons, plates, cups, flames, tree trunks, amd so on.


Objects can also be non material objects like light, shadow, magnetic fields and so on.


Material objects are made of substances, non material objects are not. But both are real.


Matter is the general term for all substances.


Substances are not the things themselves, they are types of matter, like iron, water, air, earth, plastic, wood and so on.


But a material object like a plastic spoon is not a substance, it is made of a type of matter which is a substance called plastic.


OK so substances can also have many appearances, solid, liquid or gas as in the examples shown.

Substances can be combined to form more complicated substances.


One way to combine substances is just to mix them together.

So concrete is a mixture of sand, stones, cement and water.

But the proportions of the mixture are not fixed or exact.

One lump of concrete can contain more stone or more cement than another.

But the substance is still concrete.

Concrete is a mixture.


Mixtures can be made with constant or variable proportions, but the individual components that make it up can always be divided out by physical/mechancial means.

You can chip the stones out of set concrete, you can filter the earth out of a mixture of earth and water (mud) and so on, you can remove the iron cans from rubbish with a magnet etc.


Another way to combine substances is to form compounds.

The substances that form compounds cannot be separated by mechanical means.

Further compounds always and only come in fixed proportions.


Water is a compound that always contains exactly twice as much hydrogen as oxygen and nothing else.


Iron, hydrogen and oxygen are examples of elements.


The most basic or simplest substances are called elements.

Elements cannot be broken down into simpler substances.

Iron is an element, water and air are not.


I have described compounds and mixtures and given water as an example.


Here is a question for you


Air is made of a combination of oxygen, nitrogen and carbon dioxide.


Is air a mixture or a compound?

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