We are asked to find pK_{a} for the following reaction

HNX_{3}^{+}(aq) + H_{2}O(l) ⇌ NX_{3}(aq) + H_{3}O^{+}(aq)

** NX _{3} + H_{2}O **

Hence, the K_{a} of HNX_{3}^{+}(aq) can be calculated from the K_{b} of NX_{3}. **K _{a} and K_{b} are** connected by the

$\overline{){{\mathbf{K}}}_{{\mathbf{w}}}{\mathbf{=}}{{\mathbf{K}}}_{{\mathbf{a}}}{\mathbf{\xb7}}{{\mathbf{K}}}_{{\mathbf{b}}}}$

K_{w} is a constant and is *temperature-dependent*. The value of K_{w} at the given temperature (25°C) is:

**K _{w} = 1.0x10^{-14} @ 25**

On the other hand, pKa can be calculated from Ka using the following equation:

If K_{b} for NX_{3} is 4.5×10^{−6} , what is the the pK_{a} for the following reaction?

HNX_{3}^{+}(aq) + H_{2}O(l) ⇌ NX_{3}(aq) + H_{3}O^{+}(aq)

Express your answer numerically to two decimal places.

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