Answer:
Option (e) is correct
Explanation:
According to Henderson - hasel balch equation
For H₂CO₃ / HCO₃⁻
[tex]pH = pka + log\frac{[HCO^-_3]}{[H_2CO_3]} \\\\= 6.4 + log\frac{[HCO^-_3]}{[H_2CO_3]} -------(1)[/tex]
For H₂PO₄⁻ / HPO₄²⁻
[tex]pH = pka + log\frac{[HPO_4^2^-]}{[H_2PO_4^-]} \\\\= 7.2 + log\frac{[HPO_4^2^-]}{[H_2PO_4^-]}-----(2)[/tex]
Now ph for buffer mixture is 6.4
pH = 6.4 in eqn(1) [HCO₃⁻]- [H₂CO₃]
pH = 6.4 in eqn(2) [H₂PO₄⁻] > [HPO₄²⁻]
Option (e) is correct
The [tex]\rm pK_a[/tex] is the acid dissociation constant for the compound. At pH 6.4, the number of species is [tex]\rm [H_2CO_3]=[HCO_3^-],\; and\;[H_2PO_4^-]>[HPO_4^{2-}][/tex].
The acid dissociation is constant in the pH at which, the acid is dissociated into its component ions. At the pH equivalent to acid dissociation constant, the concentration of reactant compound and ions is equal.
The acid dissociation constant [tex]\rm H_2CO_3[/tex] is 6.4. At pH 6.4, the concentration of hydrogen carbonate and bicarbonate ions is the same.
Thus, [tex]\rm [H_2CO_3]=[HCO_3^-][/tex].
The pH below the acid dissociation constant has the predominant amount of the reactant than the product, as dissociation is not favored.
Thus, [tex]\rm [H_2PO_4^-]>[HPO_4^{2-}][/tex]
Therefore, At pH 6.4, the number of species is [tex]\rm [H_2CO_3]=[HCO_3^-],\; and\;[H_2PO_4^-]>[HPO_4^{2-}][/tex]. Thus, option e is correct.
Learn more about the acid dissociation constant, here:
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