SALTS

CONTENT
⦁ Definition of Salts
⦁ Characteristics of Salts
⦁ Preparation of Salts
⦁ Types of Salts
⦁ Uses of Salts
⦁ Hydrolysis of Salts

Definition of Salts
A salt is a compound formed when all or part of the ionizable hydrogen of an acid is replaced by metallic or ammonium ions. It consists of all aggregation of positively charged metallic ion and negatively charged acid ions.
Characteristics of Salts
⦁ Water of crystallization: This can be defined as the definite amount of water that some substances chemically combine with when they form salt and such salts are referred to as hydrated salts. When heated, they give off their respective water of crystallization and by so doing become anhydrous salt. When hydrated, they are crystalline in shape but when heated and the water of crystallization is released, there’s a loss of crystalline shape. Examples of salt with water of crystallization are sodium trioxosulphate(IV) decahydrate, Na2SO3 .10H2O, Iron(II) tetraoxosulphate(VI) heptahydrate, FeSO4.7H2O, sodium trioxocarbonate(IV) decahydrate, Na2CO3.10H2O etc.
⦁ Efflorescence: This is the loss of part or all of the water of crystallization from a crystalline salt when exposed to the atmosphere to form a lower dehydrate or the anhydrous salt; e.g. Na2CO3 10H2O (washing soda).
⦁ Deliquescence: This is a phenomenon in which a substance absorbed moisture (water) from the atmosphere when exposed and turn into solution; e.g. CaCl2 , FeCl3, , CuCl2, ZnCl2 etc.
⦁ Hygroscopic: This is a phenomenon in which a substance absorbed moisture (water) from the atmosphere when exposed and does not turn into solution but merely become sticky or moist; e.g. sodium trioxonitrate(V), potassium trioxonitrate(V). Hygroscopic substances are commonly employed as drying agents or desiccants.
Drying agents or desiccants are substances that have strong tendency to absorb moisture or water. They are used to dry gases in the laboratory. A drying agent cannot be used if it reacts with the substance to be dried;, that is why H2SO4 cannot be used to dry ammonia gas because they will react to form ammonium tetraoxosulphate (vi).
2NH3 +   H2SO4     →      (NH4)2SO4
EVALUATION
⦁ State three properties of salts with two examples each.

Preparation of Salts
The method chosen to prepare a salt depends largely on (a) its solubility in water (b) its stability to heat.
A. Preparation of Soluble Salts
1. Reaction of acid and metal: Here, the more reactive metal (Ca, Mg, Zn, Fe), directly displaces the hydrogen ion in the acid; e.g.
Zn  +  2HCl    →    ZnCl2   +  H2
2. Reaction of alkaline and acid: Salts are formed when acid reacts with alkaline; e.g.
KOH  +  HNO3     →     KNO3 + H2O
3. Dilute acid and insoluble base: A salt is formed when a dilute acid is heated and the insoluble base is added to the acid until no more bases can dissolve in the acid. E.g
2HCl +   CuO    →   CuCl2  +   H2O
B. Preparation of Insoluble Salts
1. Double decomposition: This is done by missing two compounds, one containing the metallic radical and the other the acidic radical of the required insoluble salt; e.g.
H2SO4 + CuO     →     CuSO4  +  H2O
2. Combination of constituent elements: This involves the combination of the elements that make up the insoluble salt; e.g.
Fe  +  S    →     FeS
2Fe + 3Cl2   →    2FeCl3

EVALUATION
⦁ Name two salts which can be prepared by titration and, describe two methods of preparing soluble salts.
⦁ Explain with two examples the term efflorescence
⦁ When is a substance said to be deliquescence. Explain with examples.
⦁ Common salt (NaCl) becomes wet on exposure to air. Explain.
⦁ What are dehydrating agents? Explain the function of fused calcium (II) chloride in the desiccator.

Types of Salts
There are five main types of salts. They are: normal salts, acid salts, basic salts, double salts and complex  salts.
1. Normal salt: Formed when all the replaceable hydrogen ions in the acid have been completely replaced by metallic ions.
H2SO4 + ZnO     →     H2O + ZnSO4
HCl   + NaOH     →       NaCl + H2O
2. Acid salt: Formed when the replaceable hydrogen ions in acids are only partially replaced by a metal and are acidic to litmus paper; e.g.
H2SO4 + NaOH     →      NaHSO4 + H2O
3. Basic salt: Formed when there is an insufficient acid to neutralize a base; e.g.
Ca(OH)2 + HCl    →     Ca(OH)Cl  +   H2O
Zn(OH)2+ HCl     →     Zn(OH)Cl    +   H2O
4. Double salt: Ionizes to produce three different types of ions in solution. Usually two of these are positive charged, while the other is negatively charged; e.g. potash alum or aluminum potassium tetraoxosulphate(vi)duodecahydrate, KAl(SO4)2. 12H2O
KAl(SO4)2.12H2O   →    K+   +   Al3+  +  2   +  12H2O
5. Complex salts: Complex salts ionize in water to complex ions; e.g. sodium tetrahydroxozincate (II), Na2Zn(OH)4 and potassium hexacyanoferrate (II), K4Fe(CN)6.
K3[Fe(CN)6]    →   3K+  +    [Fe(CN)6]3-

Uses of Salts
⦁ Sodium chloride is used in preserving food
⦁ Salt are used as drying agents and antifreeze
⦁ Salt is used in soap making process to separate soap from glycerin
⦁ It is used in softening of water e.g. Na2CO3 10H2O
⦁ Used in stabilizing dirty roads
⦁ Used in the production of toothpaste.
Hydrolysis of Salts
When salt is dissolved in water a solution which is either acidic or basic is formed. The reaction of a salt with water to form acidic or basic solution is known as Hydrolysis. However, when other salts are dissolved in water solutions that are not neutral are formed. These solutions may either be acidic or alkaline.
The solution of a salt of strong acid and a weak base will be acidic while a salt of a weak acid and a strong base will be alkaline.
Examples:
NH4Cl + H2O   →     NH4OH + HCl
CuSO4+ 2H2O    →     Cu(OH) 2   +   H2SO4
Na2CO3 + 2H2O    →     2NaOH   +  H2CO3
K2CO3+ 2H2O     →        2KOH +H2CO3

EVALUATION
⦁ Give five types of salts with examples.
⦁ What are the uses of salts? Define hydrolysis.
⦁ Differentiate between a normal salt and acidic
⦁ What is salt? Give five examples.