compare and contrast how NH3 and Ca(OH)2 form OH- ions in water.

Question

NH3 and Ca(OH)2 form OH- ions in water

 

Answer 1

I would disagree slightly with the previous answer only because Ca(OH)2 would be initially classed as an Arrhenius base since it "donates" on OH- group.  Of course, it is also a Bronsted base and a Lewis base.  Also, NH3 is classed as a Bronsted base as it is a proton acceptor (and yes, it is also a Lewis base).  The equations presented in the previous answer are absolutely correct; my only disagreement is with the classification description. A minor point indeed.

Answer 2

You have to know that both of them are bases, however, NH3 is a Lewis base, while Ca(OH)2 is more of a Bronsted base. 

 

As a Lewis base, NH3 has an electron lone pair that can attract hydrogen ion in the water, so NH3 + H2O—->(NH4)⁺ + (OH)^- .

 

On the other hand, Ca(OH)2 is a Bronsted base, so it can dissociate (OH)^- itself. For Ca(OH)2, we have Ca(OH)₂–>Ca²⁺ + 2(OH)^-