Question

The pH of glycine at the first half equivalence point is 2.34 and that at the second half equivalence point is 9.60. At the equivalence point (the first inflection point) pH is:
A) 3.63
B) 2.34
C) 5.97
D) 11.94

Answer 1

Equivalence point is a point in titration at which the amount of titrant added can completely neutralize the analyte solution. At this equivalence point in an acid-base titration, the number of moles of base becomes equal to the number of moles of acid and then the solution is only left with salt and water.
In this numerical we have to find the pH so the formula used will be: $pH = \dfrac{{pK{a_1} + pK{a_2}}}{2}$, here $pk{\alpha _1}$ represents dissociation constant at first value and the $pk{\alpha _2}$ represents the dissociation constant of second value.

Complete step by step answer:
In the given question
The pH of glycine at first equivalence point is = $pK{a_1}$​​= 2.34 (Where $pK{a_1}$is the negative log of acid dissociation constant at first equivalence point)
The pH of glycine at first equivalence point is = $pK{a_2}$​​= 9.60 (Where $pK{a_2}$is the negative log of acid dissociation constant at second equivalence point)
Hence, we know that the pH at equivalence point is given by:
$pH = \dfrac{{pK{a_1} + pK{a_2}}}{2}$
$\Rightarrow pH = \dfrac{{2.34 + 9.60}}{2} = 5.97$
Therefore, the pH at equivalence point is 5.97.

So, the correct answer is Option C.

Note: pH value in chemistry is a method of measurement of the acidic or the basic nature of a solution or substance. A substance or solution is acidic if it has high concentration of hydrogen ions and is basic if it has high concentration of hydroxide ions or the low concentration of hydrogen ions.
pH has an important role in reflecting the chemical properties of the solutions. pH have various activities such as control of the microbial or the biological functions, properties of certain chemicals and their behaviour.