Question

Write the reaction and the corresponding Kb equilibrium expression for each of the following substances (acting as a base in water). (Type your answer using the format H3PO4 for H3PO4, (NH4)2CO3 for (NH4)2CO3, [NH4]+ for NH4+, and [Ni(CN)4]2- for Ni(CN)42-. Use the lowest possible coefficients.)
(a) NH3
(b) CN -
(c) pyridine, C5H5N
(d) aniline, C6H5NH2

Answer 1

Answer: (a) NH3 + H20 ⇔ NH4⁺ + OH⁻ Kb =  $\frac{ [NH4][OH]}{[NH3]}$

(b) CN⁻ + H20 ⇔ HCN⁺ + OH⁻ Kb =  $\frac{ [HCN][OH]}{[CN]}$

(c) C5H5N + H20 ⇔ C5H5NH⁺ + OH⁻ Kb = $\frac{[C5H5NH][OH]}{ [C5H5N]}$

(d) C6H5NH2 + H20 ⇔ C6H5NH3⁺ + OH⁻ Kb = $\frac{[C6H5NH3][OH]}{[C6H5NH2] }$

Explanation: There are ways to calculate the strength of acids and bases. The pH is more commom but there is pKa, pKb, Ka and Kb. Ka and Kb are the dissociation constant for acids and bases, respectively.

Using the balanced equation of dissociation, Kb is calculated by dividing the concentration of the products with the concentration of the reagent.