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2.5mLof 2//5M weak mono-acidic base (K(b...

`2.5mL`of `2//5M` weak mono-acidic base `(K_(b) = 1 xx 10^(-12)` at `25^(@)C)` is titrated with `2//15M HCI` in water at `25^(@)C`. Find the concentration of `H^(o+)` ions at equivalence point. `(K_(w) = 1 xx 10^(-14)at 25^(@)C)`
a. `3.7 xx 10^(-13)M` b. `3.2 xx 10^(-7)M`
c. `3.2 xx 10^(-2)M` d. `2.7 xx 10^(-2)M`

A

`3.7 xx10^(-13)M`

B

`3.2 xx10^(-7)M`

C

`3.2 xx10^(-2)M`

D

`2.7 xx10^(-2)M`

Text Solution

Verified by Experts

The correct Answer is:
D
`BOH +HCl to BCl +H_(2)O`
`{:(B^(+),+,H_(2)O, hArr,BOH,+,H^(+)),(c(1-h),,,,ch,,ch):}`
Volume of HCl used ` = (2.5 xx2/5)/(2//15) = 7.5 ` ml
Concentration of Salt , ` c = (2.5 xx2/5)/(10) = 0.1 M `
` (CH^(2))/(1-h) = (K_(w))/(K_(b))`
On Solving , h = 0.27 (hence h cannot be ignored with respect to 1 )
`[H^(+)] = Ch = 0.1 xx 0.27 = 2.7 xx10^(-2) M `
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