Question

A 0.0884 M solution of a weak base has a pH of 11.79. What is the identity of the weak base?Weak Base KbEthylamine (CH3CH2NH2) 4.7 x 10-4Hydrazine (N2H4) 1.7 x 10-6Hydroxylamine (NH2OH) 1.1 x 10-8Pyridine (C5H5N) 1.4 x 10-9Aniline (C6H5NH2) 4.2 x 10-10A) hydrazineB) pyridineC) anilineD) ethylamineE) hydroxylamine

Answer 1

Answer:

The base must be ethylamine.

Explanation:

The pH of solution of a weak base gives us an idea about the Kb of the base.

$pOH=14-pH$

$pOH=14-11.79=2.21$

$pOH=-log[OH^{-}]$

$[OH^{-}]=0.0062M$

The relation between Kb and hydroxide ion concentration is:

$Kb=\frac{[OH^{-}]^{2}}{[base]}$

$Kb=\frac{0.0062X0.0062}{0.0884}=4.34X10^{-4}$

Thus the weak base must be ethylamine.