wiz-icon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

A 1 L aqueous solution is made by mixing NH4OH and HCl solution at 25C.
This can act as a basic buffer when :

A
Molar concentration of weak base is more than the molar concentration of strong acid i.e [NH4OH]>[HCl]
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
Molar concentration of weak base is less than the molar concentration of strong acid i.e [NH4OH]<[HCl]
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
Molar concentration of weak base is equal to the molar concentration of strong acid i.e [NH4OH]=[HCl]
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
A basic buffer is always formed by NH4OH and HCl
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

The correct option is A Molar concentration of weak base is more than the molar concentration of strong acid i.e [NH4OH]>[HCl]
Weak Base (WB) and Strong Acid (SA)
Basic buffer (pH >7) : It is the mixture solution of a weak base and a salt of this weak base with a strong acid.
Consider the combination of NH4OH and HCl
Condition-1 where[WB]>[SA]
NH4OH(aq)+HCl(aq)NH4Cl(aq)+H2O(l)
4 3
1 0 3 3

As 1 mol of NH4OH is left,
The reaction here is NH4OH(aq)NH+4(aq)+OH(aq)
1(1α) α+3 1α
3
α is too small as compared to the concentrations of [NH+4] and [NH4OH]
We get Kb=[NH+4][OH][NH4OH]
[OH]=Kb[NH4OH][NH+4]
By addition of a small amount of H+ ions equilibrium will move in forward direction by the same amount and same number of OH ions are produced. Hence there is no significant change in the pH is observed.
This acts as a buffer solution.

Condition-2 where[WB]=[SA]
NH4OH(aq)+HCl(aq)NH4Cl(aq)+H2O(l)
3 3
0 0 3 3
(Hydrolysis occurs here as there is complete consumption of acid and base as a result salt is only left in solution. This is not a buffer)

Condition-3 where [WB]<[SA]
NH4OH(aq)+HCl(aq)NH4Cl(aq)+H2O(l)
3 4
0 1 3 3
Hydrolysis of NH4Cl can be neglected as degree of hydrolysis was already small and common ion effect due to H+ coming from HCl will further decrease it.
So, The [H+]total can be assumed to be from HCl only andpH can be directly found from this [H+].
This is not buffer solution

flag
Suggest Corrections
thumbs-up
0
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Buffer Solutions
CHEMISTRY
Watch in App
Join BYJU'S Learning Program
CrossIcon