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

The base must be ethylamine.

Step-by-step 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=([OH^(-)]^(2))/([base])`

`Kb=(0.0062X0.0062)/(0.0884)=4.34X10^(-4)`

Thus the weak base must be ethylamine.