Understanding the weak base NH3 in water - .

[christian0710]

Hi i have a general question concerning the behavior of a weak base NH3 in water.
If we have a reaction between a weak base and water

NH3 + H2O = NH4(+) + OH(-)

NH3 is a weak base with respect to the base ,OH(-), produced from water. This means that the lone pair of OH(-) will Attack a high procentage of the NH4+ that NH3 want’s to produce from water.

Is it correctly assumed that the weak base NH3 is actually competing against 2 bases in a water solution: It’s competing against OH because OH reacts with NH4+ but it also competes aginst water, because the following equilibrium must be true
NH4+ + H2O = H3O(+) + NH3
So actually NH4+ reacts with OH and H2O to form NH3…Correct?

A last question:
Is OH(-) a more reactive base than water? For instance if we have put a weak acid into water, would the OH(-) produced from waters autoinoization reaction prefer to attack the weak acid more than water itself?

 

[jbsteele]

Yes, it is correctly assumed that the weak base NH3 is competing against two bases in a water solution. NH4+ will react with both OH− and H2O to form NH3. Yes, OH− is a more reactive base than water. If a weak acid is added to water, OH− would be more likely to attack the weak acid than water itself.