Question

A student is given a solution of phenol red of unknown concentration. Solutions of phenol red are bright pink under basic conditions. (a) The student uses a pH probe and determines that the pH of the solution is 11.20. Calculate the hydrogen ion concentration, [H ], in the solution of phenol red.

Answer 1

The  hydrogen ion concentration, [H ], in the solution of phenol red solution of pH 11.20 is 6.3 X $10^{-12}$ moles/litre.

Explanation:

Data given:

basic solution of phenol red is given as it has pH of 11.2

hydrogen ion concentration = ?

the hydrogen ion concentration is calculated by using the following formula:

pH = -$log_{10}$ [$H^{+}$]

Rearranging the equation:

[$H^{+}$]  = $\frac{1}{10^{pH} }$

Putting the values in the above equation:

[$H^{+}$] = $\frac{1}{10^{11.2} }$

[$H^{+}$] = 6.3 X $10^{-12}$ moles/litre

The hydrogen ion concentration is very small and the solution of phenol red is basic in nature. The pH of 11.2 also indicates that solution is basic and teh color of the solution is bright pink.