Hydrolysis is reaction involving the breaking of bond in a molecule using in water thereby forming ions in solution. It can be referred to as the reverse of neutralization reaction. Hydrolysis often leads to change in the pH of salt. Most normal salts can undergo hydrolysis to form acidic or basic solutions.
Strong Weak
Other examples of normal salts that will dissolve in water to produce neutral solutions of pH = 7 are; KCl, KNO3, NaNO3, Na2SO4, K2SO4 etc.
Strong Weak
Other examples of normal salts that dissolve in water to produce acidic solutions (pH less than 7) are; Ca(NO3)2, FeCl3, AlCl3, ZnCl2, FeSO4 etc.
Strong Weak
Other examples of normal salts that are basic in solution (pH greater than 7) are; K2CO3, Na2S, K2S, NaCN, CH3COONa etc.
CH3COONH4(aq) + H2O(l) CH3COOH(aq) + NH4OH(aq)
Weak Weak
Other examples are (NH4)2CO3, (NH4)2S etc
GENERAL PROPERTIES OF SALTS
PHYSICAL PROPERTIES OF SALTS
Efflorescent salts lose weight and their crystalline appearance when heated or exposed to the atmosphere.
Na2CO3.10H2O(s) Na2CO3.H2O(s) + 9H2O(g)
CuSO4.5H2O(s) CuSO4(s) + 5H2O(g)
DRYING AGENTS
Deliquescence and hygroscopic compounds are used as drying agents because of their high affinity for water. They are also called dehydrating agents or desiccants. A drying agent is not used if it reacts with the substance to be dried e.g. conc. Tetraoxosulphate (VI) acid cannot be used to dry ammonia gas because both can react together.
Other examples of desiccants are; silica gel (for all gases), calcium chloride (for all gases except ammonia), calcium oxide (for ammonia), phosphorus (V) oxide (for all gases except ammonia) etc.
SALTS
A salt is a compound formed when the replaceable hydrogen atoms in an acid are wholly or partially replaced by a metallic ion or ammonium ion. Example:
a. When the hydrogen atom in HCl is replaced by sodium ion (Na+), Sodium Chloride (NaCl) is formed.
b. When two of the replaceable hydrogen atoms in H2SO4 are replaced by potassium ions (K+), potassium tetraoxosulphate(VI) [K2SO4] is formed.
c. When one of the hydrogen atoms in H2SO4 is replaced by potassium ion (K+), potassium hydrogen tetraoxosulphate (VI) [KHSO4] is formed.
d. When the hydrogen atom in trioxonitrate (V) acid is replaced by sodium ion (Na+), sodium trioxonitrate (V) [NaNO3] is formed.
TYPES OF SALT
1. NORMAL SALT: This is a salt formed when all the hydrogen atoms in an acid are completely replaced by a metallic ion or ammonium ion. Examples:
a. Sodium chloride, NaCl formed from HCl (Monobasic acid)
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
b. Potassium tetraoxsulphate (VI), K2SO4 formed from H2SO4 (dibasic acid)
H2SO4(aq) + 2KOH(aq) K2SO4(aq) +2 H2O(l)
c. Calcium tetraoxphosphate (V), Ca3(PO4)2 formed from H3PO4 (tribasic acid)
2H3PO4(aq) + 3Ca(OH)2(aq) Ca3(PO4)2(aq) +6H2O(l)
d. Ammonium chloride, NH4Cl formed from HCl (monobasic acid)
2HCl(aq) + Na2O(s) 2NaCl(aq) + H2O(l)
N:B – A monobasic acid forms only one type of salt which is a normal salt.
2. ACIDIC SALT: This is the salt formed when the hydrogen atoms in a polybasic acid is partially replaced by a metallic ion. Example:
a. Potassium hydrogen tetraoxosulphate (VI), KHSO4.
H2SO4(aq) + KOH(aq) KHSO4(aq) + H2O(l)
b. Sodium hydrogen tetraoxosulphate (VI), NaHSO4.
2H2SO4(aq) + Na2O(aq) 2NaHSO4(aq) + H2O(l)
c. Sodium dihydrogen tetraoxophosphate (V), NaH2PO4.
H3PO4(aq) + NaOH(aq) NaH2PO4(aq) + H2O(l)
N:B – Acid salts are acidic because they dissolve to yield hydrogen ion (H+) in water.
NaHSO4 ⇌ Na+ + H+ + SO42−
3. BASIC SALT: This is the salt formed by partial replacement the hydroxide ions in a metallic hydroxide. Examples:
a. Lead hydroxide trioxonitrate (VI), Pb(OH)NO3.
HNO3(aq) + Pb(OH)2(s) Pb(OH)NO3(aq) + H2O(l)
b. Zinc hydroxide chloride, Zn(OH)Cl.
NaOH(aq) + ZnCl2 Zn(OH)Cl(s) + NaCl(aq)
c. Magnesium hydrogen trioxonitrate (V), Mg(OH)NO3.
NaOH(aq) + Mg(NO3)2(aq) Mg(OH)NO3(s) + NaNO3(aq)
4. DOUBLE SALT/MIXED SALT: Double salts are formed when an acid is partially neutralized by a base and then completely neutralized by another base. Also, double salts occur when hot concentrated aqueous solutions of two simple salts are mixed and cooled to form one compound (usually the resulting crystalline compound [double salt] is hydrated i.e. contains water of crystallization). Examples:
a. Ammonium iron (II) tetraoxosulphate (VI) dodehydrate, (NH4)2Fe(SO4)2.12H2O.
This is formed from cooling mixed solutions of ammonium tetraoxosulphate (VI) and iron(II)tetraoxosulphate (VI) salts. This is iron(II) alum, a purple crystalline solid.
b. Potassium alum: Potassium aluminium tetraoxosulphate (VI), KAl(SO4)2.12H2O.
This is a white crystalline solid often used as a coagulant.
N:B – Double salts ionize to produce three different kinds of ions in solution. Two cations and an anion.
KAl(SO4)2 ⇌ K+ + Al3+ + 2SO42−
(NH4)2Fe(SO4)2 ⇌2 NH4+ + Fe2+ + 2SO42−
5. COMPLEX SALT: Complex salt is a salt that contain complex ion. It usually contains two different types of ions in a solution. One ionizes and the other which do not ionize when in solution but form the complex ions i.e. ions consisting of charged group of atoms. Complex salts are also called co-ordination compounds.
Examples:
1. Sodium tetrahydroxozincate (II), Na2Zn(OH)4.
This is formed from sodium salt and zinc oxide or hydroxide.
2NaCl(aq) + Zn(OH)2(s) + 2H2O(l) Na2Zn(OH)4(aq) + 2HCl(aq)
2. Potassium hexacyanoferrate (II), K4Fe(CN)6.
This could be gotten from iron (II) salt and potassium cyanide.
6KCN + FeSO4 K4Fe(CN)6 + K2SO4
N:B – Complex salts exhibit the properties of the complex ion formed when in solution.
Na2Zn(OH)4 ⇌ 2Na+ + [Zn(OH)4]2−
K4Fe(CN)6 ⇌ 4K+ + [Fe(CN)6]4−
SALTS
A salt is a compound formed when the replaceable hydrogen atoms in an acid are wholly or partially replaced by a metallic ion or ammonium ion. Example:
a. When the hydrogen atom in HCl is replaced by sodium ion (Na+), Sodium Chloride (NaCl) is formed.
b. When two of the replaceable hydrogen atoms in H2SO4 are replaced by potassium ions (K+), potassium tetraoxosulphate(VI) [K2SO4] is formed.
c. When one of the hydrogen atoms in H2SO4 is replaced by potassium ion (K+), potassium hydrogen tetraoxosulphate (VI) [KHSO4] is formed.
d. When the hydrogen atom in trioxonitrate (V) acid is replaced by sodium ion (Na+), sodium trioxonitrate (V) [NaNO3] is formed.
TYPES OF SALT
1. NORMAL SALT: This is a salt formed when all the hydrogen atoms in an acid are completely replaced by a metallic ion or ammonium ion. Examples:
a. Sodium chloride, NaCl formed from HCl (Monobasic acid)
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
b. Potassium tetraoxsulphate (VI), K2SO4 formed from H2SO4 (dibasic acid)
H2SO4(aq) + 2KOH(aq) K2SO4(aq) +2 H2O(l)
c. Calcium tetraoxphosphate (V), Ca3(PO4)2 formed from H3PO4 (tribasic acid)
2H3PO4(aq) + 3Ca(OH)2(aq) Ca3(PO4)2(aq) +6H2O(l)
d. Ammonium chloride, NH4Cl formed from HCl (monobasic acid)
2HCl(aq) + Na2O(s) 2NaCl(aq) + H2O(l)
N:B – A monobasic acid forms only one type of salt which is a normal salt.
2. ACIDIC SALT: This is the salt formed when the hydrogen atoms in a polybasic acid is partially replaced by a metallic ion. Example:
a. Potassium hydrogen tetraoxosulphate (VI), KHSO4.
H2SO4(aq) + KOH(aq) KHSO4(aq) + H2O(l)
b. Sodium hydrogen tetraoxosulphate (VI), NaHSO4.
2H2SO4(aq) + Na2O(aq) 2NaHSO4(aq) + H2O(l)
c. Sodium dihydrogen tetraoxophosphate (V), NaH2PO4.
H3PO4(aq) + NaOH(aq) NaH2PO4(aq) + H2O(l)
N:B – Acid salts are acidic because they dissolve to yield hydrogen ion (H+) in water.
NaHSO4 ⇌ Na+ + H+ + SO42−
3. BASIC SALT: This is the salt formed by partial replacement the hydroxide ions in a metallic hydroxide. Examples:
a. Lead hydroxide trioxonitrate (VI), Pb(OH)NO3.
HNO3(aq) + Pb(OH)2(s) Pb(OH)NO3(aq) + H2O(l)
b. Zinc hydroxide chloride, Zn(OH)Cl.
NaOH(aq) + ZnCl2 Zn(OH)Cl(s) + NaCl(aq)
c. Magnesium hydrogen trioxonitrate (V), Mg(OH)NO3.
NaOH(aq) + Mg(NO3)2(aq) Mg(OH)NO3(s) + NaNO3(aq)
4. DOUBLE SALT/MIXED SALT: Double salts are formed when an acid is partially neutralized by a base and then completely neutralized by another base. Also, double salts occur when hot concentrated aqueous solutions of two simple salts are mixed and cooled to form one compound (usually the resulting crystalline compound [double salt] is hydrated i.e. contains water of crystallization). Examples:
a. Ammonium iron (II) tetraoxosulphate (VI) dodehydrate, (NH4)2Fe(SO4)2.12H2O.
This is formed from cooling mixed solutions of ammonium tetraoxosulphate (VI) and iron(II)tetraoxosulphate (VI) salts. This is iron(II) alum, a purple crystalline solid.
b. Potassium alum: Potassium aluminium tetraoxosulphate (VI), KAl(SO4)2.12H2O.
This is a white crystalline solid often used as a coagulant.
N:B – Double salts ionize to produce three different kinds of ions in solution. Two cations and an anion.
KAl(SO4)2 ⇌ K+ + Al3+ + 2SO42−
(NH4)2Fe(SO4)2 ⇌2 NH4+ + Fe2+ + 2SO42−
5. COMPLEX SALT: Complex salt is a salt that contain complex ion. It usually contains two different types of ions in a solution. One ionizes and the other which do not ionize when in solution but form the complex ions i.e. ions consisting of charged group of atoms. Complex salts are also called co-ordination compounds.
Examples:
1. Sodium tetrahydroxozincate (II), Na2Zn(OH)4.
This is formed from sodium salt and zinc oxide or hydroxide.
2NaCl(aq) + Zn(OH)2(s) + 2H2O(l) Na2Zn(OH)4(aq) + 2HCl(aq)
2. Potassium hexacyanoferrate (II), K4Fe(CN)6.
This could be gotten from iron (II) salt and potassium cyanide.
6KCN + FeSO4 K4Fe(CN)6 + K2SO4
N:B – Complex salts exhibit the properties of the complex ion formed when in solution.
Na2Zn(OH)4 ⇌ 2Na+ + [Zn(OH)4]2−
K4Fe(CN)6 ⇌ 4K+ + [Fe(CN)6]4−
TEACHER: MISS EMELDA OKPALANWEZE
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