First slide

Factors influencing acidic strength, across the period and down the group

Question

Statement I: Higher order ionisation constant ( $(K_{a_{2}}, K_{a_{3}})$ are smaller than the lower order ionisation constant ( $K_{a_{1}}$ ) of a polyprotic acid.
Statement II: It is more difficult to remove a positively charged proton from a negative ion due to electrostatic forces.

Moderate

A

Both statements I and II are correct.
B

Statement I is incorrect and statement II is correct.
C

Statement I is correct and statement II is incorrect.
D

Both statements I and II are incorrect.

Solution

Higher order ionisation constants $(K_{a_{2}}, K_{a_{3}})$ are smaller than the lower order ionisation constani ( $K_{a_{1}}$ ) of a polyprotic acid. The reason for this is that it is more difficult to remove a positively charged proton from a negative ion due to electrostatic forces.
This can be seen in the case of removing a proton from the uncharged $H_{2} {CO}_{3}$ as compared from a negatively charged ${HCO}_{3}^{-}$ .
Similarly, it is more difficult to remove a proton from a doubly charged ${HPO}_{4}^{2 -}$ anion as compared to $H_{2} {PO}_{4}^{-}$ .

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