Mixing the acid solution with an
alkaline solution will produce salt and water. However, salt may be
acidic, alkaline or neutral. Properties depend on the type of salt and
acid components basanya. Salts can be formed from strong acids with strong
bases, weak acids with strong bases, strong acids with weak bases or weak acids
with weak bases. Thus, the acid-base properties of a salt can be determined
from the strength of the acid and alkaline constituent. Nature of the
acidity or alkalinity of the salt is caused by some soluble salts react with
water. The process of partial dissolution of the salt reacts with water is
called hydrolysis (hydro meaning water and lysis meaning
decomposition).
A.
Salt
of Strong Acid with Strong Bases
Strong
acids and strong bases react to form salt and water. Cation and anion
salts derived from strong electrolyte is not hydrolyzed, so that this solution
is neutral, pH of the solution is equal to 7.
Example
KCl
solution comes from the strong base KOH ionized cation and anion perfect
shape. KOH is ionized into H + and Cl - . Each
ion does not react with water, the reaction can be written as follows.
KCl (aq) → K + (aq) +
Cl - (aq)
K + (aq) +
H 2 O (l) →
Cl - (aq) +
H 2 O (l) →
B.
Salts
of Weak Bases with Strong Acids
Salts
formed from strong acids with weak bases having partial hydrolysis (partial) in
water. These salts contain cations are experiencing acid
hydrolysis. This salt solution is acidic, pH <7.
Example
Ammonium
chloride (NH 4 Cl) is a salt formed from a strong acid,
HCl in a weak base NH 3 . HCl will perfectly ionized
into H + and Cl - while the NH 3 in
the solution will partially ionized form NH 4 + and
OH - .Anion Cl - derived from strong
acids can not be hydrolyzed, while the cation NH 4 + derived
from a weak base can be hydrolyzed.
NH 4 Cl (aq) → NH 4 + (aq) +
Cl - (aq)
Cl - (aq) +
H 2 O (l) →
NH 4 + (aq) +
H 2 O (l) → NH 3
(aq) + H 3 O + (aq)
Hydrolysis
reaction of ammonium (NH 4 + ) is an
equilibrium reaction.This reaction produces oxonium ion (H 3 O + )
that is acidic (pH <7).In general the reaction is written:
BH + +
H 2 O → B + H 3 O+
C.
Salts
of Weak Acids with Strong Bases
Salts formed from a weak acid with
strong base having a partial hydrolysis in water. This salt contains the
anion alkaline hydrolysis experience. This salt solution is alkaline
(pH> 7).
Example
Sodium acetate (CH 3 COONa)
is formed from a weak acid CH 3 COOH and a strong base
NaOH. CH 3 COOH would form a partially ionized
CH 3 COO - and Na + . Anion
CH 3 COO - derived from a weak acid
which can be hydrolyzed, while the cations Na + comes from
a strong base that can not be hydrolysed.
CH 3 COONa (aq) → CH 3 COO - (aq) +
Na + (aq)
Na + (aq) +
H 2 O (l) →
CH 3 COO - (aq) +
H 2 O (l) → CH 3 COOH (aq) +
OH - (aq)
Hydrolysis reaction of acetic acid
(CH 3 COO - ) is an equilibrium
reaction. This reaction produces OH ions - that is
alkaline (pH> 7). In general the reaction is written:
A - + H 2 O → HA
+ OH-
D.
Salt
of Weak Acid with Weak Bases
Weak acids with weak
bases to form salts of hydrolyzed total (perfect) in water. Both cations
and anions can be hydrolyzed in water. This saline solution can be acidic,
alkaline, or neutral. It depends on the strength of cation to anion ratio
in the reaction with water.
Example
A weak acid HCN is
mixed with a weak base, NH 3 is formed salt NH 4CN. HCN
partially ionized in water to form H + and CN - ,
while NH 3 in a partially ionized water to form NH4 + and
OH-. Base anion CN - and acid cation NH 4 + can
be hydrolyzed in the water.
NH 4 CN (aq) → NH 4 + (aq) +
CN - (aq)
NH 4 + (aq) +
H 2 O → NH 3 (aq) +
H 3 O (aq)+
CN - (aq) +
H 2 O (e) → HCN (aq) +
OH - (aq)
The nature of the
solution depends on the relative strength of acids and bases its constituent
(Ka and Kb)
If Ka <Kb (weaker
acid than in bases), the anion will be hydrolyzed and the solution more
alkaline.
if Ka> Kb (stronger
acid than in bases) then be hydrolyzed cations in solution more acidic.
Ka = Kb (as weak acid with a base) the solution is neutral.
What are examples of hydrolysis of concept of salt in life?
BalasHapus