#### • Class 11 Physics Demo

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# Examples of Hydrated Salts

Acids and bases when react together, neutralize each other to produce salt and water. However, they mostly react in an aqueous solution. An aqueous solution is a solution where the solvent is usually water. Acids produce hydrogen ions in solution. Most acids have the general formula HA, where A minus is an anion, which are negatively-charged ions. Bases produce hydroxide ions in solution. Most bases have the form BOH, where B plus is a cation, which are positively-charged ions. Neutralization happens because hydrogen ions and hydroxide ions react to produce water.

The anion of acid and the cation of base then react to form a salt. For example, hydrochloric acid and sodium hydroxide neutralize each other to form the salt sodium chloride and water. Similarly, sulphuric acid and ammonium hydroxide neutralize to form a salt ammonium sulphate and water. Another example is the reaction of black copper oxide and acetic acid in the vinegar, to form copper acetate and water. The copper acetate is water soluble and dissolves away, leaving a clean copper metal surface. However, when exposed to air this copper acetate reacts with the oxygen in the air to form blue-green copper carbonate.

All non-metal oxides are acidic in nature and react with water to form acids and they react with bases to form salts. For example sulphur trioxide reacting with barium hydroxide to give the salt barium sulphate and water.

Another example is reaction of phosphorus pentoxide with sodium hydroxide to form sodium phosphate and water. Most non-metal oxides are acidic and form oxy-acids, which in turn yield hydronium ions (H3O+) in aqueous solution. Some of the salts contain water in their crystal. This water content is called as water of crystallisation and such salts are called as hydrated salts. You know that the formula of gypsum CaSO4. 2H2O and formula for plaster of Paris is CaSO4. $\frac{1}{2}$H2O.

What do you think about water molecules shown in formula?  Why we wrote it just next to main formula separated by dot? This is known as water of crystallization. It indicates the number of water molecules which are chemically combined with the salt in its crystalline state. These water molecules combine in a definite molecular proportion. The presence of water in the molecule affects the geometry of crystal and other physical properties such as colour, melting point etc.

Such type of salts is known as hydrous salts. These salts are better known with their common names instead of their chemical names. Some common hydrous or hydrated salts with their common name are as given below;

 Name Chemical Formula Common Name Barium Chloride BaCl2.2H2O Calcium Chloride CaCl2, 6H2O Dow flake Calcium Nitrate Ca(NO2)2.4H2O Lime salt petre or Norwegian salt petre Calcium Sulphate CaSO4 .2H2O Gypsum Calcium Sulphate Hemi Hydrate (CaSO4)2.H2O Plaster of Paris Copper (II) Chloride CuCl2. 2H2O Copper (II) Sulphate CuSO4,5H2O Blue vitriol Ferrous Sulphate FeSO4.7H2O Green vitriol Magnesium Sulphate MgSO4.7H2O Epsom salt Potassium Aluminium Sulphate K2SO4.Al2 (SO4)3.24H2O Potash alum Sodium Carbonate Deca Hydrate Na2CO3, 10 H2O Washing soda (crystal) Sodium Carbonate Mono Hydrate Na2CO3. H2O Washing soda (powder) Sodium Sulphate Na2SO4. 10H2O Glauber's Salt Zinc Sulphate ZnSO4.7H2O White vitriol