Question

The pH at the equivalence point of titration may differ from 7.0 because of
A.The self-ionization of water
B.Hydrolysis of the salt formed
C.The indicator used
D.The concentration of the standard solution

Answer 1

Hint: pH is the value that expresses the acidity or alkalinity of a solution on a logarithmic scale. If the pH is 7, this means that the solution is neutral. If pH \[ < 7\] the solution is acidic whereas if the pH \[ > 7\] the solution is alkaline or basic.

Complete step by step answer:
The equivalence point of a titration is a point at which the amount of titrant is added is enough to neutralize the analyte solution. For acid-base titration, at the equivalence point, the number of moles of acids is equal to the number of moles of base.
Therefore, in the case of strong acid and strong base, the number of moles of acid and base becomes equal at the equivalence point. So, the pH at the equivalence point of this titration is always 7.0(neutral). but this is only true for strong acid and strong base. For example,
When a strong acid and a strong alkali or base combine, it forms a neutral salt i.e., having \[pH = 7\] . The reaction of the formation of NaCI is –
 \[NaOH + HCl \to NaCl + {H_2}O\]
Since sodium chloride NaCI is neutral, it does not affect the \[[{H^ + }]\] and \[[O{H^ - }]\] in water and the concentration of NaCI solution does not alter the pH of the solution. Therefore, the pH is 7.
In the other case, the pH at the equivalence point of titration may differ from 7.0 because of the hydrolysis of salt formed. For example,
Aluminum chloride on reacting with water results in the formation of aluminum hydroxide and hydrochloric acid. The chemical equation of the reaction is:
 \[AlC{l_3} + 3{H_2}O \to Al{(OH)_3} \downarrow + 3HCl\]
Here, aluminum hydroxide is a weak base i.e. it partially dissociates in the solution and is sparingly soluble in water, and therefore it is in precipitate form. Hydrochloric acid is a strong acid and can completely dissociate into respective cation and anion, \[{H^ + }\] and \[C{l^ - }\] . In which the pH becomes slightly acidic (less than 7) is called cation hydrolysis.
So, the correct answer is, B.

Note:In chemistry, pH is a scale to measure the acidity or basicity of a solution. It is can be calculated by the formula \[pH = - \log {\left[ H \right]^ + }\] , where \[{\left[ H \right]^ + }\] is the molar concentration of hydrogen ion present in the solution. Molar concentration is also called molarity means the number of moles of a particular solute in a solvent per litre volume of solution.