Assertion When weak diprotic acid dissociates with its dissociation constants and then \) is almost equal to Reason for so \) is negligible \)

Both Assertion and Reason are incorrect

Chemistry · Various concepts of acids and bases (Arrhenius, Bronsted Lowry and Lewis) and their ionization, acid-base equilibria (including multistage ionization) and ionization constants

Assertion When weak diprotic acid dissociates with its dissociation constants an

Assertion When \( 0.1 ~ M \) weak diprotic acid \( H_{2} A \) dissociates with its dissociation constants \( \boldsymbol{K}_{\boldsymbol{a}_{1}}=\mathbf{1 0}^{-\mathbf{3}} \) and \( \boldsymbol{K}_{\boldsymbol{a}_{2}}=\mathbf{1 0}^{-\mathbf{8}} \) then \( \left[A^{2-}\right] \) is almost equal to \( 10^{-3} M \) Reason \( \operatorname{since} K_{a_{2}} \ll K_{a_{1}} \) for \( 0.1 M H_{2} A, \) so \( \left[\boldsymbol{A}^{2-}\right] \) is negligible \( \mathbf{w} . \mathbf{r . t .}\left[\boldsymbol{H} \boldsymbol{A}^{-}\right] \)

A. Both Assertion and Reason are correct and Reason the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Step-by-step solution

For a 0.1 M diprotic acid H2A with Ka1=10^-3 and Ka2=10^-8, the concentration of A^2- is approximately 10^-8 M, not 10^-3 M, because [A^2-] ≈ Ka2 = 10^-8 M. Thus, the assertion is false. The reason states that [A^2-] is negligible compared to [HA-] due to Ka2 << Ka1, which is true; however, since the assertion is false, the pair is evaluated as both incorrect in the context of the given options. Note: The reason alone is correct, but the options do not include 'assertion false, reason true', so D is the closest match.

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Step-by-step solution

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