Q85P - Chemistry: Molecular Nature Of Matter And Change

Question

Write an empirical formula for each of the following:

(a) Ethylene glycol, car antifreeze, molecular formula ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}{\mathbf{O}}_{\mathbf{2}}$ .

(b) Per-oxo-di-sulfuric acid, a compound used to make bleaching agents, molecular formula ${\mathbf{H}}_{\mathbf{2}}{\mathbf{S}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{8}}$.

Step-by-Step Solution

Answer

(a) The empirical formula for ethylene glycol is ${\mathbf{CH}}_{\mathbf{3}}\mathbf{O}$.

(b) The empirical formula for per-oxo-di-sulphuric acid is ${\mathbf{HSO}}_{\mathbf{4}}$ .

Step 1:Definition of empirical formula

A chemical formula that gives the simplest ratio of elements present in a compound but not the actual numbers of atoms, is known as the empirical formula.

Step 2: Empirical formula for Ethylene glycol

As seen from the formula, Ethylene glycol, ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}{\mathbf{O}}_{\mathbf{2}}$ , contains carbon, hydrogen 

and oxygen.

 $$\begin{gathered} {\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}{\mathbf{O}}_{\mathbf{2}}\mathbf{=}\mathbf{C}\mathbf{:}\mathbf{H}\mathbf{:}\mathbf{O}\mathbf{:}\mathbf{:}\mathbf{2}\mathbf{:}\mathbf{6}\mathbf{:}\mathbf{2} \\ \mathbf{simplestratio}\mathbf{,}\mathbf{C}\mathbf{:}\mathbf{H}\mathbf{:}\mathbf{O}\mathbf{:}\mathbf{:}\mathbf{1}\mathbf{:}\mathbf{3}\mathbf{:}\mathbf{1} \end{gathered}$$

 So,${\mathbf{CH}}_{\mathbf{3}}\mathbf{O}$ is the empirical formula for ethylene glycol

Step 3: Empirical formula for Per-oxo-di-sulphuric acid

It's clear from the formula that per-oxo-di-sulphuric acid,${\mathbf{H}}_{\mathbf{2}}{\mathbf{S}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{8}}$ , contains hydrogen, 

Sulphur and oxygen.

 $$\begin{gathered} {\mathbf{H}}_{\mathbf{2}}{\mathbf{S}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{8}}\mathbf{=}\mathbf{H}\mathbf{:}\mathbf{S}\mathbf{:}\mathbf{:}\mathbf{O}\mathbf{:}\mathbf{:}\mathbf{2}\mathbf{:}\mathbf{2}\mathbf{:}\mathbf{8} \\ \mathbf{simplestratio}\mathbf{,}\mathbf{H}\mathbf{:}\mathbf{S}\mathbf{:}\mathbf{O}\mathbf{:}\mathbf{:}\mathbf{1}\mathbf{:}\mathbf{1}\mathbf{:}\mathbf{4} \end{gathered}$$

 So,${\mathbf{HSO}}_{\mathbf{4}}$ is the empirical formula for per-oxo-di-sulphuric acid.