Question

Classify the following as mixtures: heterogeneous or homogeneous, or pure substances, elements or compounds:

(i) sugar dissolved in water

(ii) sea water

(iii) rust

(iv) sugar

(v) mercury in a thermometer

(vi) steel

(vii) soda water

(viii) sand and water

Answer 1

Pure substance: A substance that is made of a single type of particle having the same chemical nature.

1. Pure substances are further classified into elements and compounds.
2. Elements: A pure substance that can neither be reduced further nor can be formed by physical or chemical methods and is made up of same type of atoms.
3. Compounds: It is a substance that is formed by mixing two or more elements in a defined ratio.

Mixtures: It is a substance made by mixing two or more pure substances in an undefined proportion.

1. Mixtures are further classified into homogeneous and heterogeneous.
2. Homogeneous mixtures: A mixture is said to be homogeneous if it has a uniform composition throughout.
3. Heterogeneous mixtures: A mixture having a variable composition of components is said to be heterogeneous in nature.

Classifying the substances:

(i) Sugar dissolved in water - It is a homogeneous mixture having a uniform composition.

(ii) Sea water - It is a heterogeneous mixture of water, salts and many dissolved gases.

(iii) Rust - It is a compound chemically known as iron oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$.

(iv) Sugar - It is a compound of carbon, hydrogen and oxygen having a molecular formula of ${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}$.

(v) Mercury in a thermometer - It is an element that contains one type of atom.

(vi) Steel - It is a homogeneous mixture of iron and carbon fused together with one or more other metals or nonmetals.

(vii) Soda water -It is a homogeneous mixture of carbon dioxide dissolved in water.

(viii) Sand and water- They are a heterogeneous mixture as they can be distinguished separately by naked eyes.