Question

1g of hydrogen is found to combine with 80g of bromine . 1 g of calcium combines with 4g of bromine .The equivalent mass of calcium is:
A.10
B.20
C.40
D.80

Answer 1

Equivalent weight (which is also known as gram equivalent) is the mass of one equivalent, that is the mass of a given substance which will combine with or displace a fixed quantity of another substance.

Complete step by step answer:
The equivalent weight of an element is the mass which combines with or displaces 1.008 gram of hydrogen or 8.0 grams of oxygen or 35.5 grams of chlorine. These values correspond to the atomic weight divided by the usual valence.
Atomic mass in an atom or group of an atom is the sum of the masses of protons, neutrons and electrons.
For an element relative atomic mass is the average mass of the naturally occurring isotopes of that element relative to the mass of an atom of 12C. Which means one atom is given a relative atomic mass of exactly 12.
Atomic mass = Mass of protons + Mass of neutrons + Mass of electrons
the valency of an element is the number of electrons an atom of the element uses to combine with atoms of other elements
or , it is the combining power of an atom of the element
-One gram of hydrogen combines with 80 gm of bromine.
So, equivalent weight of bromine =80 gm
As 4 g of bromine react with 1 g of $Ca$
So, 160 g of bromine combines with =$\dfrac{1}{4}\times 160$ =40g
∴ Equivalent mass of calcium = $\dfrac{atomic\text{ }mass}{valency}$ =$\dfrac{40}{2}$ =20

Note:
The number of parts by mass of a substance that combines with or displaces 1.008 parts by mass of hydrogen or 8.0 parts of oxygen or 35.5 parts of chlorine is called its equivalent mass (EM).