Question

Classify the following substance as element, compound or mixture:

Chalk

Answer 1

Chalk i.e.; Calcium carbonate $\left({\mathrm{CaCO}}_3\right)$ can be classified as a compound.

• In this, the elements Calcium$\left(\mathrm{Ca}\right)$, Carbon$\left(\mathrm{C}\right)$ , and Oxygen $\left(\mathrm{O}\right)$ are chemically combined in a fixed ratio by mass.
• The properties of the compound (chalk) are different from the elements it is made up of.
• Chalk can be broken down into its elements by chemical methods only that can break the bonds between its elements.

Compound: A compound is a pure substance in which elements combine chemically in a fixed composition to give a compound.

• They can be broken down into elements that make up the compound by using chemical or electrochemical methods.
• Example: Water$\left({\mathrm{H}}_2\mathrm{O}\right)$, Common salt i.e. Sodium chloride $\left(\mathrm{NaCl}\right)$

Element: An element is a pure substance that cannot be split into simpler substances.

• Example: Hydrogen $\left({\mathrm{H}}_2\right)$, Copper $\left(\mathrm{Cu}\right)$ etc.

As chalk can be broken down into its constituent elements, it is not an element.

Mixture: When two or more substances (elements or compounds or an element and compound) are mixed in any proportion.

• The components of a mixture can be separated by physical methods of separation.
• Example: A mixture of Sand and Iron $\left(\mathrm{Fe}\right)$ can be separated by the use of a magnet (physical process) where Iron gets attracted to the magnet leaving behind sand.

As elements of chalk can not be separated by physical methods of separation and it does not have a variable composition, chalk is not a mixture.