General Properties of Salts

Concept Explanation

General Properties of Salts

General Properties of Salts:

Salts are the white crystalline powder formed due to neutralization reaction of an acid and a base. Salts show following general properties:

1. Melting and boiling points:

Salts are mostly solid which melt as well as boil at high temperature.

2. Water of crystallization:

Salts are found as crystals with water molecules present in them. This water is called water of crystallization and such salts are called hydrated salts. E.g.: copper sulphate $CuSO_4.5H_2O$ . On heating, hydrated salts lose their water of crystallization, crystals lose their shape, color and change to a powdery substance. The hydrated salt that have lost their water of crystallization are called anhydrous salts.

3. Hydrated and Anhydrous Salts:

The crystals of some salts have a fixed number of water molecules (called water of crystallization) loosely associated with them such salts are called hydrated salts. These hydrated salts on heating lose their water of crystallisation and change to powdery substance called anhydrous salt.

4. Reaction with an Acid:

When a salt reacts with an acid, another salt and acid are formed. For example, when sodium chloride is heated with sulphuric acid, sodium hydrogen sulphate (at low temperature) and then sodium sulphate (at high temperature) are produced and hydrogen chloride gas is evolved. $NaCl+ H_2SO_4rightarrow NaHSO_4+ HCl ;;; (At ;low ;temperature)$ $2NaCl+ H_2SO_4rightarrow Na_2SO_4+ 2HCl ;;; (At ;high ;temperature)$

5. Reaction with a Base:

A salt reacts with a base to produce another salt and base.

$(NH_4)_2SO_4 + 2NaOHrightarrow Na_2SO_4+ 2NH_4OH$

6. Reaction with a Metal:

Sometimes, a salt solution may react with a metal. For example, when an iron nail is dipped into an aqueous solution of copper sulphate, copper gets deposited on the surface of the nail and the ferrous sulphate formed remains in the solution. This reaction shows that iron is more reactive than copper. Thus, a more reactive metal can displace a less reactive metal from a solution of its salt.

$CuSO_4+ Ferightarrow FeSO_4+ Cu$

7. Behavior of Salts towards Water:

Salts are soluble in water. Eg: sodium chloride, potassium sulphate, lead chloride, copper carbonate etc are soluble in water.When a salt is dissolved in water, the solution may be neutral, acidic or alkaline. This depends upon the nature of the salt used.

A normal salt derived from a strong acid and a strong base gives a neutral solution. For example, the aqueous solutions of NaCl and $K_2SO_4$ are neutral to litmus.

A normal salt derived from a weak acid and a strong base gives an alkaline solution. For example, the aqueous solutions of both sodium carbonate $Na_2CO_3$ and sodium acetate ( $CH_3COONa$ ) are alkaline.

A salt derived from a strong acid and a weak base gives an acidic solution. For example, both aluminium chloride ( $AlCl_3$ ) and ammonium chloride ( $NH_4Cl$ ) make acidic aqueous solutions.

Solutions of acidic salts are acidic to litmus, i.e., these solutions turn blue litmus paper red. For example, a solution of sodium hydrogensuiphate ( $NaHSO_4$ ) turns blue litmus paper red. Sodium hydrogen carbonate ( $NaHCO_3$ ) solution, however, is slightly alkaline.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Which of the following are correct : (a) The hydrated salts on heating lose their water of crystallisation and change to powdery substance called anhydrous salt. (b) The molecular formula of copper sulphate is $CuSO_4.5H_2O$ which is a hydrated salt. (c) Salts are mostly solid which melt as well as boil at high temperature.
A. Only (a) and (b) are correct.	B. Only (b) and (c) are correct.	C. Only (a) and (c) are correct.	D. All of these.
Right Option : D
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Question : 2

Which of the following is an acidic salt?
A. $ZnSO_4$	B. $Zn(NO)_2$	C. NaCI	D. $NaHSO_4$
Right Option : D
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Question : 3

Hydrated salts are found as crystals with water molecules present in them. This water is called _______________ .
A. Water of crystallization	B. Solubility in water	C. Melting and boiling points	D. None of these .
Right Option : A
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