Question

What are the primary chemical components present in a phosphate buffer at ph 7.4? H3po4 and po43–?

Answer 1

Answer :

The correct answer for primary component of phosphate buffer at pH = 7.4 is H₂PO₄⁻ and HPO₄²⁻ .

Buffer solution :

It is a solution of mixture of weak acid and its conjugate base OR weak base and its conjugate acid . It resist any change in solution when small amount of strong acid or base is added .

Capacity of a good buffer :

A good buffer is identified when pH = pKa .

From Hasselbalch - Henderson equation which is as follows :

$pH = pka + log \frac{[A^-]}{[HA]}$

If [A⁻] = [HA] ,

pH = pka + log 1

pH = pKa

This determines that if  concentration of  weak acid  and its conjugate base are changed in small quantity , the capacity of  buffer to maintain a constant pH is greatest at pka .  If the amount of [A⁻] or [HA] is changed in large amount , the log value deviates more than +/-  1M and hence pH .

Hence Buffer has best capacity at pH = pka .

Phosphate Buffer :

Phosphate may have three types of acid-base pairs at different pka ( shown in image ).

Since the question is asking the pH = 7.4

At pH = 7.4 , the best phosphate buffer will have pka near to 7.4 .

If image is checked the acid - base pair  " H₂PO₄⁻ and HPO₄²⁻  has pka 7.2 which is near to pH = 7.4 .

Hence we can say  , the primary chemical component of phosphate buffer at pH = 7.4  is H₂PO₄⁻ and HPO₄²⁻  .