just one unit also means change in [H + ] by a factor of . Similarly, when the hydrogen ion concentration, [H + ] changes by a factor of , the value of pH changes by units. Now you can realise why the change in pH with temperature is often ignored. Measurement of pH of a solution is very essential as its value should be known when dealing with biological and cosmetic applications.
The pH of a solution can be found roughly with the help of pH paper that has different colour in solutions of different pH. Now-a-days pH paper is available with four strips on it. The different strips have different colours (Fig. .
) at the same pH. The pH in the range of - can be determined with an accuracy of ~ . using pH paper. Fig.
. pH -paper with four strips that may have different colours at the same pH For greater accuracy pH meters are used. pH meter is a device that measures the pH-dependent electrical potential of the test solution within . precision.
pH meters of the size of a writing pen are now available in the market. The pH of some very common substances are given in Table . (page ). Problem .
The concentration of hydrogen ion in a sample of soft drink is . × – M. what is its pH ? pH = – log[ .
} = . Therefore, the pH of the soft drink is . and it can be inferred that it is acidic. Problem .
Calculate pH of a . × – M solution of HCl. Table . The Ionization Constants of Some Selected Weak Acids (at 298K) Acid Ionization Constant, K a Hydrofluoric Acid (HF) .
× – Nitrous Acid (HNO ) . × – Formic Acid (HCOOH) . × – Niacin (C H NCOOH) . × – Acetic Acid (CH COOH) .