Salts

Salts:

Salts are Ionic Compounds. A salt is formed when a metallic ion or an ammonium ion (NH₄⁺) replaces one or more Hydrogen Ions of an acid.

A Salt contains a positive metal ion and a negative non – metal ion.

Example:

Zn(OH)₂   + H₂SO₄ZnSO₄    2H2O

 

Water of Crystalization:

• Many salts combine with water molecules to form crystals . These water molecules are known as water of crystallization.
• Salts that contain Water of Crystallization are called Hydrated Salts.
• Salts that do not contain water of crystallization are called Anhydrous Salts.

Anhydrous Salts – Powder form

Hydrous Salts – Crystal / Perfectly Dry

Examples:

Copper(II) Sulphate:  (Cu SO₄) –  CuSO₄.5H20

Magnesium Sulphate (MgSO₄) – MgSO₄.7H20

Sodium Carbonate (Na₂CO₃) – Na₂CO₃.10H20

Zinc Sulphate (ZnSO₄)  –  ZnSO₄.7H20

Removing Water of Crystallization:

When a hydrated salt is heated, water of crystallization is given off.

 

Soluble and In Soluble Salts:

 

Preperation Of Salts:

Titration Method:

• Salt that has to be made should be soluble.
• Salt starters should be soluble.

Only Acid + Alkali titration can be done.

Alkali – Soluble Base

Metal Oxides / OH Of Group # 1 and 2 as all are soluble

 

• Common acids used in titration:

HCl, HNO_3, H₂SO₄

 

Apparatus Needed: Burette, Pipette and Conical Flask

Indicators:

Phenolphthalein:

• Acid – colourless
• Alkali – Pink

Methyl Orange:

• Acid – Red
• Alkali – Yellow

 

Example of Salt made through Titration:

MgSO₄

Reagents / Starters:

Mg(OH)₂  and   H₂SO₄

Equation: 

Mg(OH)₂  +  H₂SO₄ MgSO₄ +H₂O

Explaination:

Mg(OH)₂  is added by means of a pipette to a conical flask. A few drops of phenolphthalein are added. Then H₂SO₄ is poured into the conical flask using a burette.

The end point of the titration is reached when the phenolphthalein changes its colour from pink to colourless.

The volume of H₂SO₄ requires to reach the end point is noted. Then the whole procedure is repeated without addition of phenolphthalein.

The solution is then evaporated under sunlight to form bigger crystals of MgSO₄

 

Excessive Reagent Method:

• Salt that has to be made should be soluble.
• Salt starters should not be soluble.

Example of Salt made through Excessive Reagent Method:

Zn(NO₃)

ZnO  + 2HNO₃ Zn(NO₃)₂   + H₂O

Pour 10ml of Hno3 into a beaker using a pipette. Add excessive amount of ZnO into the beaker containing HNO₃.

Precipitates of excess ZnO wil form at the bottom of the beaker.

Using filteration filterate the ZnO from Zn(NO₃)₂ solution.

Zn(NO₃)₂ Solution is then heated over a burner flame in a china dish. It is then allowed to cool slowly. Crystals formed and are dried between the pieces of filter paper.

Or

Evaporate Zn(NO₃)₂ solution under sunlight crystals of Zn(NO₃)₂ will form after same time.

 

Precipitation:

• Salt that has to be made should not be soluble.
• Salt starters should be soluble.

Example of Salt made through Precipitation:

CaCo₃

CaCl₂  +  Na₂CO₃CaCO₃    +  NaCl

Add CaCl₂ into a beaker that already contains Na2co3. Precipitates of CaCO₃ will form at the bottom of the beaker. Separate the newly formed insoluble CaCO₃ using filtration.

CaCO₃ is then evaporated under sunlight, crystals are formed.

 

Key:

• All soluble salts of Group 1 and 2 except Ca sulphate and Carbonate are prepaired by titration method.
• All soluble esalts of transitional metals are prepaires by reacting the oxides with acids through excessive reagent method.
• All insoluble salts are prepaired by percepitaion method.