Name: Law of Multiple Proportions
Uploaded: 2019-07-19
Duration: 6 min 43 s
Description: The Law of multiple proportions is applicable only when two elements combine to form two or more compounds. Watch this video to know how this law is applicable.

Question

Define equivalent mass. What is the difference between equivalent mass and gram equivalent?

Accepted Answer

Equivalent weight unlike molecular weight is proportional mass of chemical entities which combine or displace other chemical entities.

The equivalent mass of an element is a number which expresses how many parts by mass of the element combines with or displaces from compound $1.008$ parts by mass of hydrogen or $8$ parts by mass of oxygen or $35.45$ parts by mass of chlorine.

It is not always possible to apply this classic definition to determine equivalent weights of chemical entities. It is so because, we can not conceive of reactions involving chemical entities with three named reference of hydrogen, oxygen and chlorine. Generally, we are limited to determination of equivalent weights of elements and few compounds by using this definition of equivalent weight.

A more workable definition is given as:

$Equivalent weight, E = \frac{Molecular weight, M}{Valence factor, x}$ .

Clearly, determination of equivalent weight amounts to determining valence factor “ $x$ ”. Here, we shall classify chemical entities and the techniques to determine “ $x$ ”.

Equivalent weight of an element:

In the case of an element, the equivalent weight is defined as:

$Equivalent weight, E = \frac{Atomic weight, A}{Valence factor, x}$ .

Note that atomic weight substitutes molecular weight and valency substitutes valence factor in the definition. Valencies of hydrogen, calcium and oxygen are $1, 2$ and $2$ respectively. Hence, their equivalent weights are $\frac{1}{1} = 1, \frac{40}{2} = 20$ and $\frac{16}{2} = 8$ respectively.

Gram equivalent (g eq):

It is equal to mass in grams numerically equal to equivalent weight. If the mass of a chemical entity is “ $g$ ” grams, then the given mass contains gram equivalents given by:

$Gram equivalent (g eq) = \frac{g}{E}$ .

This formula is widely used to express grams of substance in terms of gram equivalent and vice-versa.

One equivalent of any substance reacts with one equivalent of the other substance to produce one equivalent of each of the products. Thus, it is evident that all substances combine or appear on the basis of an equivalence. The equivalent mass or equivalent weight expressed in gram is called gram-equivalent mass or gram-equivalent weight.

Define equivalent mass. What is the difference between equivalent mass and gram equivalent?

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