Question

# The dissociation constants of two acids, $$HA_{1}$$ and $$HA_{2}$$, are $$4.5 \times 10^{-4}$$ and $$1.8 \times 10^{-5}$$ respectively. If both are having equal concentrations, then the relative strength of the acids is:

A
5:2
B
2:5
C
5:1
D
1:5

Solution

## The correct option is B $$5:1$$The dissociation of acid is given by the following equation: $$HA \rightarrow H^+ + A^-$$The given acids have a very low dissociation constant, i.e., the $$HA$$ concentration can be assumed to be unchanged.Therefore, $$[ H^+ ] = \sqrt{ \dfrac{K_a}{c} }$$.Since, the concentration is assumed to be constant, the relative strength $$= \dfrac{H^+_{HA_1}}{H^+_{HA_2}} = \sqrt{\dfrac{45}{1.8}}=5:1$$.Option C is correct.Chemistry

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