Borek said:Actually question is about formic acid and Ka value of 1.8x10-4 is correct.
Check calculation of pH of a weak acid lecture.
pH is a measure of the acidity or basicity of a solution. It is important in chemistry because it helps us understand the properties and behavior of different substances, as well as their reactions with other substances. pH also plays a role in many biological processes and is essential for maintaining the balance of our body fluids.
The pH of an aqueous solution of weak acid HCOOH can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([HCOOH]/[HCOO-]), where pKa is the acid dissociation constant of HCOOH, [HCOOH] is the concentration of the weak acid, and [HCOO-] is the concentration of its conjugate base. Alternatively, you can also use a pH meter or pH indicator to measure the pH directly.
A strong acid is an acid that dissociates completely in water, producing a high concentration of hydrogen ions (H+), while a weak acid only partially dissociates, resulting in a lower concentration of H+. This is reflected in their respective pH values, with strong acids having a pH of less than 7 and weak acids having a pH closer to 7.
The concentration of a weak acid directly affects its pH because it determines the ratio of undissociated acid to its dissociated products. As the concentration of the weak acid increases, the concentration of hydrogen ions also increases, resulting in a lower pH. Conversely, decreasing the concentration of the weak acid will result in a higher pH.
The pH of a weak acid solution can be affected by temperature through its effect on the equilibrium constant (Ka) of the acid. As temperature increases, the equilibrium shifts towards the products, resulting in a greater dissociation of the weak acid and a decrease in pH. Conversely, a decrease in temperature will shift the equilibrium towards the reactants, resulting in a lower dissociation and a higher pH.