1.

A buffer solution with pH 9 is to be prepared by mixing NH_(4)Cl and NH_(4)OH. Calculate the number of moles of NH_(4)Cl that should be added to one litre of 1.0 M NH_(4)OH. [ K_(b) = 1.8 xx 10^(-5)]

Answer»

3.4
2.6
1.5
1.8

Solution : `pH = -LOG K_(B) + log. (["Salt"])/(["ACID"])`
`pH = -log[1.8 xx 10^(-5)] + log.(["Salt"])/(1.0)`
`9 = 4.7 + log.(["Salt"])/(1.0)`
`log.(["Salt"])/(1.0) = 9 - 4.7 = 4.3`
`(["Salt"])/(1.0)= "Antilog" (1)/(4.3), ["Salt"] = 1.8`.


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