What is the $pH$ of a $0.10molL^-1$ solution of ammonium ion....for which $pK_a=9.26$ ?

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Answer 1 · 2017-03-31T02:35:46

And the $pK_a$ of ammonium ion is..............?

We interrogate the equilibrium,

$NH_4^+ + H_2O(l) rightleftharpoons NH_3 + H_3O^(+)$

For which, $K_a=([NH_3][H_3O^+])/([NH_4^+])=10^(-9.25)$

So $10^(-9.25)=x^2/(0.10-x)$ , a quadratic in $x$ , that we can solve by successive approximation, i.e. assuming that $0.1>x$ :

Thus $x~=sqrt(10^(-9.25)xx0.10)$

$x_1=7.5xx10^-6$

$x_2=7.5xx10^-6$

Since $x=[H_3O^+]$ , $pH=-log_10(7.5xx10^-6)=5.12$

What is the pHpH of a 0.10*mol*L^-10.10*mol*L^-1 solution of ammonium ion....for which pK_a=9.26pK_a=9.26?