Answer:
the concentration of bicarbonate is [HCO₃⁻] = 0,03996 M and carbonate is [CO₃²⁻] = 3,56x10⁻⁵ M.
Explanation:
Carbonate-bicarbonate is:
HCO₃⁻ ⇄ CO₃²⁻ + H⁺ With pka = 10,25
Using Henderson-Hasselbalach formula:
pH = pka + log₁₀[tex]\frac{[CO_{3}^{2-}]}{[HCO_{3}^-]}[/tex]
7,2 = 10,25 + log₁₀[tex]\frac{[CO_{3}^{2-}]}{[HCO_{3}^-]}[/tex]
8,91x10⁻⁴ = [tex]\frac{[CO_{3}^{2-}]}{[HCO_{3}^-]}[/tex] (1)
Also:
0,040 M = [CO₃²⁻] + [HCO₃⁻] (2)
Replacing (2) in 1:
[HCO₃⁻] = 0,03996 M
Thus:
[CO₃²⁻] = 3,56x10⁻⁵ M
I hope it helps.