Final answer:
The major species in a 0.50 M HNO2 solution with Ka=4.0x10^-4 are the un-ionized acid HNO2, hydronium ions H3O+, and nitrite ions NO2-. HNO2 being a weak acid, the un-ionized form will be the predominant species.
Step-by-step explanation:
The question pertains to the determination of major species in a solution of nitrous acid (HNO2), a weak acid with a given Ka (acid dissociation constant). When HNO2 dissolves in water, it partially ionizes into H+ (or H3O+ in water) and NO2¯.
The major species in a solution of 0.50 M HNO2 with Ka = 4.0×10−4 will be the un-ionized acid HNO2, the hydronium ions H3O+, and the nitrite ions NO2¯. However, because HNO2 is a weak acid, HNO2 will predominantly exist as the un-ionized form, and the concentrations of H3O+ and NO2¯ will be much lower.
The major species in a 0.50 M HNO2 (nitrous acid) solution are HNO2 (aq) and H3O+ (aq), along with the corresponding conjugate base, NO2- (aq).
When nitrous acid is dissolved in water, it donates a proton to water, resulting in the formation of hydronium ions (H3O+) and nitrite ions (NO2-). The concentration of these species depends on the dissociation constant, Ka, which is given as 4.0×10-4.