why is ammonia a weak acid ?

Answer 1

It isn´t. It´s a weak base.

The ammonia molecule has a trigonal pyramid shape.. The nitrogen atom in the molecule has a lone electron pair, and ammonia acts as a base, a proton acceptor.This shape gives the molecule an overall dipole moment and makes it polar so that ammonia readily dissolves in water. In water a very small percentage of NH3 is converted into the ammonium cation (NH4+).


H2O + NH3 ====> NH4+ + OH-

therefore, NH3 is the weak base, whereas the ion ammonium NH4+ is the weak acid.

They are weak, because they are not completely dissociated in water . In fact the pKb is 4.75 (for strong bases, it is 1)

pKb is defined by:

pKb = −log10 Kb

where Kb is
Kb = { [NH4+] * [OH-] } / [NH3]

Answer 2

Ammonia is usually thought of as a weak base rather than a weak acid. It behaves as a base when dissolved in water. I suppose it could act as an acid as it contains hydrogen but I dont know of a situation where this happens.

Answer 3

Actually, ammonia is not an acid but rather a base, which is the chemical opposite of acid.
The most general description of what happens with a base is that it has an a lone pair of electrons in it and therefore "accepts" protons out of neutral or acidic substances it comes into contact with, and "donates" its free electron. Acid does the opposite (donates proton and accepts electrons). Like everything in nature, it's just trying to form an equality.
The reason that bases act like acids is that they cause damage through a similar method. Such a mass movement of sub-atomic particles is bound to cause cell damage.

Answer 4

Ammonia is NOT a weak acid.
Ammonia solution is a weak base/alkali.
If ammonia solution is pH tested the value will be approximately 8 or 9.

Answer 5

well ammonia is not an acid...Ammonium on the other hand could be considered as an acid maybe you got them mixed up....

(NH4+) ---> NH3 + (H+)

This reaction happens continuously in ammonia solution (which is actually ammonium and a hydroxide -- hydroxide gives the basic nature to the solution). This is why when you smell ammonia solution its smells like ammonia gas cause it tends to be released from solution!!

Answer 6

I would say that it actually depends on the context in which you're examining NH3.

Under different conditions, a compound may act as either an acid or a base. In chemistry, acid/base definitions are relative, both within a particular system of defining acids and bases (e.g. Bronsted/Lowry), as well as between different systems (e.g. if you're comparing Lewis vs Bronsted/Lowry).

Also, it is possible that the original poster wasn't actually talking about NH3 as an individual molecule. They may have seen NH2- (or the amide anion/the deprotonated form of amine or NH3) as part of an organic reaction, a context in which it frequently functions as a strong base, in which case it would make sense to ask about the strength of the conjugate acid of NH2- because we often talk about acid and base strengths relative to their conjugate acids or bases in the Bronsted-Lowry definition of acids and base.

Answer 7

Ammonia is basic NOT an acid.

When dissolved in water it becomes ammonium hydroxide ...
a weak alkali
NH4OH all acids have the H+ .

Answer 8

Because ammonia is a good base. Greater will be basicity lesser will be acidity. It all depends upon their pKa & pKb values. You can look for the table in any standard book.

You can go for Bronsted - Lowry concept.
'An acid is a substance which easily gives H+ (proton) e.g. HCl.

HCl + H2O = H3O+ + Cl-

A base is a substance which easily takes up the H+ (Proton). e.g NH3

NH3 + H2O = NH+ + OH-

There you can see that NH3 even takes up the proton from H2O so it is good base but weaker acid than even H2O.

Answer 9

the strength of an acid is determined by how readily does it transfer hydrogen ions to water.. when acid is added to water, almost all of the hydrogen ions in the acid added( if its strong) would usually 'transfer' to the water to form the hydronium ion (H3O)... as for weak acids, it's the opposite that happens

so you can say that, ammonia only transfers a small amount H+ ions to water (when H2O and NH3 is added together) or doesn't readily transfer a lot of of the ions in H2O, making it a weak acid

This differentiation is based on the Bronsted-Lowry definition of an acid and base...

if there're some confusions or questions, fell free to email me or soemthing... i hope that helps...

Answer 10

Ammonia is the only common alkali gas.

if you go back to standard grade chemistry, and drawing the shared pairs of electrons between compounds you will see that ammonia NH3 has three shared pairs and one extra pair which are called a 'lone pair' of electrons.

................LONE PAIR (negative charge)
.......................ee
..............H-ee-N-ee-H
.......................ee
.........................|
........................H

and as water is polar covalent the Hydrogen in water being less electronegative than Oxygen is slightly positive.

........O (slightly negative)
......../ \
......H H (both slightly positive)

This means the lone pair is attracted to the hydrogen in water and is able to pull off the hydrogen to form the ammonium ion NH4 + and a hydroxide ion.

As bases and alkalis produce the OH- ion we then understand that as Ammonia produces the OH- ion then it must be alkali.