A 0.0678 M solution of a weak base has a pH of 9.44. What is the identity of the weak base? Weak Base Kb Ethylamine (CH3CH2NH2) 4.7 × 10–4 Hydrazine (N2H4) 1.7 × 10–6 Hydroxylamine (NH2OH) 1.1 × 10–8 Pyridine (C5H5N) 1.4 × 10–9 Aniline (C6H5NH2) 4.2 × 10–10

The weak base is hydroxylamine

Explanation:

The general equilibrium of a weak base (A), is:

A(aq) + H₂O(l) ⇄ HA⁺ + OH⁻

Where Kb is:

Kb = [HA⁺] [OH⁻] / [A]

As both HA⁺ and OH⁻ comes from the equilibrium of A; HA⁺ = OH⁻. So, you can take:

Kb = [OH⁻]² / [A]

OH⁻ is determined from pH, thus:

pOH = -log [OH⁻]

pOH = 14 - pH

pOH = 14 - 9.44

pOH = 4.56

[OH⁻] = 10^{-4.56}

[OH⁻] = 2.75x10⁻⁵

As the concentration of the weak base is 0.0678M:

Kb = [OH⁻]² / [A]

Kb = [2.75x10⁻⁵]² / [0.0678M]

Kb = 1.1x10⁻⁸ = Kb of Hydroxylamine.

the dissociation of nickel hydroxide is follows:

the concentration of hydroxide ion is

the equilibrium constant value of nickel hydroxide is = 6.1 * 10^-^1^6 and thus equilibrium equation can be written as:

thus, concentration of ni is 0.23 * 10^-^4 mol /l