SCH 4U1
THEORIES OF ACIDS AND BASES
ACIDS AND BASES ARE BOTH ELECTROLYTES (CONDUCT ELECTRICITY IN SOLUTION) BECAUSE THEY BOTH
IONIZE IN SOLUTION.
1) ACCORDING TO THE ARRHENIUS DEFINITION:
ACIDS ARE SUBSTANCES THAT PRODUCE HYDROGEN IONS, H+ IN SOLUTION.
HCl(g) ---> H+(aq) + Cl-(aq)
(acid)
BASES ARE SUBSTANCES THAT PRODUCE HYDROXIDE IONS, OH1- IN SOLUTION.
NaOH(s) ---> Na+(aq) + OH-(aq)
(base)
2) ACCORDING TO THE BRONSTED-LOWRY DEFINITION:
ACIDS ARE PROTON DONORS AND BASES ARE PROTON ACCEPTORS.
CONSIDER THE REACTION:
H1+
NH3(g) + H2O(l) ---> NH4+(aq) + OH-(aq)
IN THIS CASE, A PROTON WENT FROM THE WATER TO THE AMMONIA GAS. WATER IS THE PROTON
DONOR (ACID) AND AMMONIA IS THE PROTON ACCEPTOR (BASE).
SINCE THE AMMONIUM ION (NH4+) CAN NOW POTENTIALLY DONATE A PROTON IT IS CALLED THE
CONJUGATE ACID OF THE BASE AMMONIA (NH3).
SINCE THE HYDROXIDE ION (OH-) CAN NOW POTENTIALLY ACCEPT A PROTON IT IS CALLED THE
CONJUGATE BASE OF WATER.
LEWIS ACIDS
CONSIDER THE FOLLOWING REACTION:
HCl(aq) + NH3(g) ---> NH4Cl(s)
THE LEWIS DEFINITION STATES:
A LEWIS ACID IS AN ELECTRON-PAIR ACCEPTOR, AND A LEWIS BASE IS AN ELECTRON-PAIR DONOR.
H1+ :NH3 --->
H
|
H - N+ - H
|
H
* remember co-ordinate
covalent bonding
H1+ RECEIVED AN ELECTRON PAIR (LEWIS ACID) AND AMMONIA DONATED AN ELECTRON PAIR (LEWIS BASE).