what is the role of water in acid and base
Answers
Answer:
Water dissociates to form ions by transferring an H+ ion from one molecule acting as an acid to another molecule acting as a base.
H2O(l) + H2O(l) <-----> H3O+(aq) + OH-(aq)
acid base
Acids react with water by donating an H+ ion to a neutral water molecule to form the H3O+ ion.
HCl(g) + H2O(l) <-----> H3O+(aq) + Cl-(aq)
acid base
Bases react with water by accepting an H+ ion from a water molecule to form the OH- ion.
NH3(aq) + H2O(l) <-----> NH4+(aq) + OH-(aq)
base acid
Water molecules can act as intermediates in acid-base reactions by gaining H+ ions from the acid
HCl(g) + H2O(l) <-----> H3O+(aq) + Cl-(aq)
and then losing these H+ ions to the base.
NH3(aq) + H3O+(aq) <-----> NH4+(aq) + H2O(l)
Explanation:
The Brnsted model can be extended to acid-base reactions in other solvents. For example, there is a small tendency in liquid ammonia for an H+ ion to be transferred from one NH3 molecule to another to form the NH4+ and NH2- ions.
2 NH3 <-----> NH4+ + NH2-
By analogy to the chemistry of aqueous solutions, we conclude that acids in liquid ammonia include any source of the NH4+ ion and that bases include any source of the NH2- ion.
The Brnsted model can even be extended to reactions that don't occur in solution. A classic example of a gas-phase acid-base reaction is encountered when open containers of concentrated hydrochloric acid and aqueous ammonia are held next to each other. A white cloud of ammonium chloride soon forms as the HCl gas that escapes from one solution reacts with the NH3 gas from the other.
HCl(g) + NH3(g) <-----> NH4Cl(s)
This reaction involves the transfer of an H+ ion from HCl to NH3 and is therefore a Brnsted acid-base reaction, even though it occurs in the gas phase.