what are the concentrations of all species present in 1.00M acetic acid at 20degree celcius ? (for HC2H3O2 Ka= 1.8x10^5)?

Consider the dissociation of HC₂H₃O₂:
_____________ HC₂H₃O₂(aq) + H₂O ⇌ C₂H₃O₂⁻(aq) + H₃O⁺(aq) …… Ka = 1.8 × 10⁻⁵
Initial: __________ 1.00 M ___________ 0 M _______ 0 M
Change: __________ -y M ___________ +y M ______ +y M
Equilibrium: __ (1.00 - y) M __________ y M ________ y M

As Ka is very small, the dissociation of HC₂H₃O₂ is to a very small extent.
We can assume that 1.00 ≫ y
Hence, [HC₂H₃O₂] at equilibrium = (1.00 - y) M ≈ 1.00 M

At equilibrium: Ka = [C₂H₃O₂⁻] [H₃O⁺] / [HC₂H₃O₂]
1.8 × 10⁻⁵ = y² / 1.00
y = √(1.8 × 10⁻⁵) = 0.00424

Ay equilibrium:
[C₂H₃O₂⁻] = [H₃O⁺] = 0.00424 M
[HC₂H₃O₂] = 1.00 M
[OH⁻] = Kw/[H₃O⁺] = (1.00 × 10⁻¹⁴) / 0.00424 M = 2.36 × 10⁻¹² M