Equilibrium Question 757

Question: The degree of dissociation of water at $ 25{}^\circ C $ is $ 1.9\times {10^{-7}} $ % and density is 1.0 g $ c{m^{-3}} $ . The ionic constant for water is

Options:

A) $ 1.0\times {10^{-10}} $

B) $ 1.0\times {10^{-14}} $

C) $ 1.0\times {10^{-16}} $

D) $ 1.0\times {10^{-8}} $

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Answer:

Correct Answer: B

Solution:

$ \underset{(1-\alpha )c}{\mathop{H_2O}},\rightarrow \underset{\alpha c}{\mathop{{H^{+}}}},+\underset{\alpha c}{\mathop{O{H^{-}}}}, $

$ \alpha =\frac{1.9\times {10^{-7}}}{100}; $ Density of water = $ \frac{1.0g}{cm^{2}} $

$ \therefore c=\frac{1}{18}\times 1000=55.56moles/l $

$ \therefore [{H^{+}}]=55.56\times 1.9\times {10^{-9}}=1.055\times {10^{-7}} $

$ \therefore K_{w}=[{H^{+}}][O{H^{-}}]={{(1.055\times {10^{-7}})}^{2}}=1.0\times {10^{-14}} $



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