Question

Define a mixture. Is mixture composition is fixed or variable.

Answer 1

Mixture :

1. A mixture is a substance which consists of two or more pure substances (elements or compounds) mixed together in any proportion so that components do not lose their identity.
2. For example - air is a mixture of several gases, seawater, petrol, soil and soft drinks.

Depending upon the nature of components which form the mixtures, we have different types of mixtures:

(i) Homogeneous mixtures:

1. A mixture is said to be a homogeneous mixture if it has the same composition throughout the sample.
2. A homogeneous mixture has no visible boundaries of separation between various constituents.
3. For example, salt solution (sodium chloride is dissolved in water), sugar solution (sugar dissolved in water)

(ii) Heterogeneous mixtures:

1. A mixture is said to be a heterogeneous mixture if it consists of two or more parts (called phases ) which have different compositions.
2. It has visible boundaries of separation of various constituents.
3. For example, salt and sulphur, a mixture of iron and sulphur, and smoke (a mixture of air and carbon particles).

A mixture is a substance with a variable composition:

1. It is composed of molecules or atoms of differing types.
2. These may have bonds between molecules (intermolecular bonds), but such bonds are weak as those formed when elements bond to form a compound.
3. Elements can be mixed in any proportion.
4. No chemical reaction occurs and individual elements will contain their identities.