Question

Assertion - Homogenous mixtures don't have fixed melting and boiling points Reason - Homogenous mixtures have uniform composition​

Answer 1

Hint: A mixture is a material made up of two or more different substances. A mixture is the physical combination of two or more substances in which the constituents don’t lose identities. Mixtures are the blending of chemical substances such as element and compounds

Complete answer:

-The temperature at which the vapour pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapour is known as the boiling point of a substance.

-The temperature at which a substance changes state from solid to liquid is known as the melting point of a substance.

-Mixture is a combination of more than one substance. When more solutes are present in a mixture, the melting and boiling point of the mixture is changed.

-Let us study this considering an example. The boiling point of water is 100∘C

. If we add 20 grams of salt in 5 litres of water, the boiling point of water is increased to 100.04∘C

. Impurities present in a solution can lower the melting and boiling point. For example, cryolite NaAlF3

is added to Aluminium oxide when heating, turning it to molten form.

-As mixtures are made up of two or more pure substances and formed as a result of their physical change. Mixtures thus have variable proportions of various components, due to which they do not have sharp melting and boiling points.

Additional information:

The mixtures are classified into two types;

- Homogeneous mixture

Homogeneous mixture is the mixture in which the components are mixed uniformly.

- Heterogeneous mixtures

Heterogeneous mixtures are the mixtures in which the components are mixed not uniformly.

Note:

Mixtures are different from chemical compounds, because-

(i) The substances or constituents of a mixture cannot be separated using physical methods such as filtration, freezing, and distillation.

(ii) There is little or no energy changes during the formation of a mixture.

(iii) Compounds have a fixed position, while mixtures have variable compositions.

(iv) Individuals of the mixtures don't lose their properties, that is they keep their properties while in compounds their properties can change.