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how to find  equivalent mass of different compound with example

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Methods Of Determination Of Equivalent Mass

Hydrogen displacement method: We know that metals react with acids to produce hydrogen. Hydrogen displacement method just uses this fact to calculate the equivalent mass. Here some mass of an element reacts with an acid to produce some amount of hydrogen gas under standard temperature and pressure (STP).

The mass of metal which displaces 11200 ml of hydrogen at NTP from an acid, alkali or alcohol is the equivalent mass of the metal.

(a) Equivalent mass of metal

(b) Equivalent mass of metal


This method is useful for metals which can displace hydrogen from acids or can combine with hydrogen (Mg, Zn, Ca, etc.) 

(ii) Oxide formation method: We have studied that metals react with oxygen and produce metal oxides, and the oxide method evaluates the mass of the metal oxide generated when some mass of a metal readily reacts with oxygen.

The mass of the element which combines with 8 grams of oxygen is the equivalent mass of the element.

(a) Equivalent mass of metal = (Mass of metal/Mass of oxygen)×8   

(b) Equivalent mass of metal 

(iii) Chloride formation method : This is another alternative method used when the above two methods aren't compatible to calculate the equivalent mass. The mass of an element which reacts with 35.5 gm. of chlorine is the equivalent mass of that element.

(iv) Neutralisation method: (For acids and bases).

Equivalent mass of acid (or base) = W/v×N 

Where ,

W = Mass of acid or base in gm.,

V = Vol. of base or acid in litre required for neutralisation

N is Normality of base or acid

(v)    Metal displacement method : It is based on the fact that one gm. equivalent of a more electropositive metal displaces one gm equivalent of a less electropositive metal from its salt solution.

(vi) Electrolytic method: The quantity of substance that reacts at electrode when 1 faraday of electricity is passed is equal to its gram equivalent mass.

Gram equivalent mass = Electrochemical equivalent  96500

The ratio of masses of two metals deposited by the same quantity of electricity will be in the ratio of their equivalent masses.                    

W1/W2 = E1/E2                                         

(vii) Double decomposition method  


(viii) Conversion method: When one compound of a metal is converted to another compound of the same metal, then


(E = Eq. mass of the metal)

(ix) Volatile chloride method


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