The compounds formed by the reaction between an acids and a bases are known as a salts.
Acid + Base → Salt + Water
Salts are ionic compounds which contain positively charged cations and negatively charged anions. During salt formation cation is coming from base and anion is coming from acid.
Example: In Sodium chloride (NaCl) formation cation sodium is coming from sodium hydroxide and anion chlorine is coming from hydrochloric acid.
NaOH + HCl → NaCl + H2O
Classification of salts:
Based on nature of the salts, they are classified into different types.
- Neutral salts
- Acidic salts
- Basic salts
- Double salts
- Complex salts
These salts are formed by the reaction between strong base and strong acid.
NaCl is neutral salt formed by the reaction of HCl with NaOH.
HCl + NaOH → NaCl + H2O
NaCl is neutral salt , if it is dissolved in water ; solution remains neutral, pH = 7 at 25°C.
Salts which are formed by the combination of strong acids and weak bases are called acidic salts.
NH4OH + HCl → NH4Cl + H2O
NH4Cl is acidic salt; if it is dissolved in water solution will be acidic.
Salts which are formed by the reaction of Strong base and weak acid are called Basic salts.
NaOH + CH3COOH→ CH3COONa + H2O
CH3COONa is a basic salt; if it is dissolved in water ,solution turns basic.
Ca(OH)Cl is formed by the partial replacement of hydroxide group from Ca(OH)2 by chloride ions of acid.
Ca(OH)2 + HCl → Ca(OH)Cl + H2O
Table below giving neutral, acidic and basic salts.
|Type of Salt||Type of Acid||Type of Base||Example of salt|
pH = 7
pH < 7
pH > 7
Some salts contain two different cations or two different anions or both. These salts are called Complex Salts. They can be further classified into 2 types :
1. Double salts 2. Coordination compounds
Salts that are formed by mixing of two simple salts which are obtained crystallization. In other words, these salts on dissolving in water loose all the ions.
Potash alum – K2SO4 Al2 (SO4)3 .24H2O
Dolomite – CaCO3.MgCO3
Coordination Compounds : These salts do not loose all the ions they consists.
[Ag(NH3)2]Cl ⇄ [Ag ( NH3 )2 ]+ + Cl–
K4[Fe(CN)6] ⇄ 4K+ + [Fe(CN)6]4-
Salts in our daily life:
Chemical name: Sodium hydrogen carbonate or Sodium bicarbonate
Molecular formula: NaHCO3
Sodium hydrogen carbonate is commenly called as baking soda.
Sodium hydrogen carbonate is used in the baking industry.
It is used in preparation of soda acid.
It is also used in foam type fire extinguishers.
Molecular formula: Na2CO3.10H2O
Chemical name : Sodium carbonate decahydrate
Adding water to sodium carbonate and this allowing this mixture to cool to forms decahydrated sodium carbonate. This is commenly called as washing soda.
Na2CO3 + 10H2O → Na2CO3.10H2O
In general sodium carbonate is prepared by passing CO2 gas through concentrated NaOH.
2NaOH + CO2 → Na2CO3 + H2O
It is a white crystalline solid. It exists as decahydrate of sodium carbonate.
When exposed to dry air and heating it loses water molecules to change into anhydrous form.
Na2CO3.10H2O + Exposure to open dry air → Na2CO3.H2O + 9H2O
Na2CO3.H2O + Heating → Na2CO3
It is soluble in water and during dilution heat will releases out.
On reaction with acids sodium carbonate releases carbon dioxide along with the formation of sodium salts and water.
Na2CO3 + HCl → 2NaCl + H2O + CO2
Sodium carbonate is used to manufacture of glass, cleansing agents, soap, glass and paper.
Bleaching powder (CaOCl2):
Bleaching powder chemically known as calcium oxy chloride.
It is prepared by the reaction between chlorine and slaked lime at about 40ºC.
Ca(OH)2 + Cl2 → Ca(OCl)Cl + H2O + Cl2
Ca(OH)2 + H2SO4 → CaSO4 + H2O + Cl2
It acts a strong oxidising agent to bleach substances.
CaOCl2 + KNO2 → CaCl2 + KNO3
CaOCl2 + H2S → CaCl2 + H2O + S
It is used to bleach cotton, linen textiles and wood pulp.
Coloured matter + Bleaching powder → Colourless product
It is also used to disinfect drinking water.
The molecules of salts which contain fixed number of water molecules in them are called hydrated salts.
In general they exists as dry in pure form.
These salts on heating loses water molecules in them and forms anhydrous salts.
Ferrous sulphateheptahydrate (FeSO4.7H2O) on heating loses water molecules in it.
FeSO4.7H2O (on heating) → FeSO4 + 7H2O
Some of the hydrated salts along with their chemical formula.
|Name of the salt||Chemical formula|
|Sodium carbonate decahydrate||Na2CO3.10 H2O|
|Zinc Sulphate heptahydrate or White vitriol||ZnSO4.7H2O|
|Magnesium sulphate heptahydrate or Epsom salt||MgSO4.7H2O|
|Potash alum||K2SO4 Al2 (SO4)3 .24H2O|
|Copper (II) sulphate pentahydrate or Blue vitriol||CuSO4.5H2O|
|Calcium sulphate dihydrate or Gypsum||CaSO4.2H2O|
Plaster of paris (CaSO4. 1/2 H2O):
Plaster of paris which is chemically called calcium sulphate hemihydrate.
Since it is brought to use from paris, called as “plaster of paris”.
It is prepared by heating of gypsum at 373K.
CaSO4.2H2O 373 K → CaSO4 1 2 H2O + 1 1 2 H2O
Gypsum Plaster of Paris Water
Uses of plaster of Paris:
- It is used as a bandage, proofing material, sealing agent.
- It is used for making statues, toys and decorative articles.
- It is also used for smoothing wall surfaces.