Question

Calculate [OH-], pH and pOH of a 0.175M KHCO3 solution at 25 degrees celsius

*WRITE IN PRINT (LEGIBLY)*

Answer 1

KHCO₃ can acts as a both acid & base. It is amphoteric in nature.

HCO₃^- is an intermediate form of an carbonic acid and carbonate ion.

We know that, for intermediate form, [H⁺ ] = K ₁ K ₂ F + K ₁ K _w / K ₁ + F

From literature ,dissociation constants of carbonic acids are K ₁ = 4.46 10 ^-07 & K ₂ = 4.69 10 ^-11

[H⁺ ] = (4.46 10 ^-07) ( 4.69 10 ^-11 ) 0.175 + ( 4.46 10 ^-07 ) ( 1.00 10 ^-14 ) /  4.46 10 ^-07 + 0.175

[H⁺ ] = 3.6605 10 ^-18 + 4.46 10 ^-21 / 0.1750

[H⁺ ] = 2.094 10 ^-17

[H⁺ ] = 4.58 10 ^-09 M

We have relation,  [H⁺ ] [ OH ^- ] = 1.00 10 ^-14

[ OH ^- ] = 1.00 10 ^-14 / [H⁺ ] = 1.00 10 ^-14 / 4.58 10 ^-09 = 2.18 10 ^-06 M

We have relation, p H = -log [H⁺ ] = - log 4.58 10 ^-09 = 8.34

We have relation, p OH = -log [ OH ^- ] = - log 2.18 10 ^-06 = 5.66

ANSWER : [H⁺ ] = 4.58 10 ^-09 M

[ OH ^- ] = 2.18 10 ^-06 M

pH = 8.34

pOH = 5.66