Question

Why does solid 1-indanone and 3,4-dimethoxybenzaldehyde become liquids with mixed together? Explain this phenomena using chemical terms.

Answer 1

When a pure solid substance is made impure by mixing with another substance, the melting point decreases. This phenomenon is called melting point depression.

Most of the organic solids are crystalline solids. These molecules have repeating units of ions which are arranged in a regular crystal lattice. This lattice is held together by means of various intermolecular forces, depending on the particular solid. When the substance melts, this intermolecular forces disrupt. The impurities disrupt the repeating units that holds the solid together thereby decreasing the input of energy required to melt the solid surrounding the impurity ions or molecules.

Here, the molecules 3,4-dimethoxybenzaldehyde and 1-indanone have a low melting point just above the room temperature. The melting point of 3,4-dimethoxy benzaldehyde and 1-indanone are 43 °C and 42 °C, respectively. When they are mixed together, the crystal structure of the crystal lattice of both molecules are interrupted and both of them melt at room temperature