Question

The pH of the solution is $6.45$ . Calculate the concentration of ${H^ + }$ ion.

Answer 1

To calculate the $pH$ of an aqueous solution we need to know the concentration of the hydronium ion in moles per liter. The pH is then calculated using the expression: pH = - log [H3O+]. $pH$ ranges from $0$ to $14$ , with $7$ being neutral. $pH$ less than $7$ are acidic while $pH$ greater than $7$ are alkaline

Complete answer:
$pH$ , quantitative measure of the acidity or basicity of aqueous or other liquid solutions. The term, widely used in chemistry, biology, and agronomy, translates the values of the concentration of the hydrogen ion which ordinarily ranges between about $1$ and ${10^{ - 14}}$ gram-equivalents per litre into numbers between $0$ and $14$ .
$pH$ is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, ${a_{{H^ + }}}$ , in a solution
$pH = - {\log _{10}}({a_{{H^ + }}}) = {\log _{10}}(\dfrac{1}{{{a_{{H^ + }}}}})$
We have $pH = 6.45$
We know that, $pH = - \log [{H^ + }]$
$\Rightarrow 6.45 = - \log [{H^ + }]$
$\Rightarrow [{H^ + }] = {10^{ - 6.45}}$
$\Rightarrow [{H^ + }] = 3.54 \times {10^{ - 7}}$ .

Additional Information:
Indicators may be used to measure $pH$ , by making use of the fact that their color changes with $pH$ . Visual comparison of the color of a test solution with a standard color chart provides a means to measure $pH$ accurately to the nearest whole number. More precise measurements are possible if the color is measured spectrophotometrically, using a colorimeter or spectrophotometer. Universal indicator consists of a mixture of indicators such that there is a continuous color change from about $pH$ $2$ to $pH$ $10$ . Universal indicator paper is made from absorbent paper that has been impregnated with universal indicator. Another method of measuring pH is using an electronic $pH$ meter.

Note:
Measurement of $pH$ below about $2.5$ and above about $10.5$ requires special procedures because, when using the glass electrode, the Nernst law breaks down under those conditions. Various factors contribute to this. It cannot be assumed that liquid junction potentials are independent of $pH$