Looking at Equivalents

A gram equivalent is also known as an equivalent (Eq) and is defined as follows:

A gram equivalent is the WEIGHT of an element or ion which combines with or replaces 1 gram of Hydrogen.

You know that 1 ATOM of Hydrogen weighs 1 gram so the gram equivalent for a substance is the weight of that substance that combines with (or replaces) 1 ATOM OF HYDROGEN.

Click on the boxes to look at some examples.
HCl
NaCl
H2S
MgCl2

Hydrochloric Acid

HCl

You can see that 1 atom of Chlorine combines with
1 atom of Hydrogen.

Thus the gram equivalent of Chlorine is the weight of
1 atom of Chlorine.
1 atom of Chlorine weighs 35.5 grams.

Thus the gram equivalent of Chlorine is 35.5 grams.
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Sodium Chloride

NaCl

You can see that 1 atom of Sodium replaces
1 atom of Hydrogen.

Thus the gram equivalent of Sodium is the weight of
1 atom of Sodium.
1 atom of Sodium weighs 23.0 grams.

Thus the gram equivalent of Sodium is 23.0 grams.
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Hydrogen Sulphide

H2S

You can see that 1 atom of Sulphur combines with
2 atoms of Hydrogen.

Thus 1/2 atom of Sulphur combines with 1 atom of Hydrogen.
Thus the gram equivalent of Sulphur is the weight of
1/2 atom of Sulphur.
1 atom of Sulphur weighs 32.1 grams.

Thus the gram equivalent of Sulphur is 32.1 / 2 grams ie 16.05 grams.
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Magnesium Chloride

MgCl2

You can see that 1 atom of Magnesium replaces
2 atoms of Hydrogen.

Thus 1/2 atom of Magnesium replaces 1 atom of Hydrogen.
Thus the gram equivalent of Magnesium is the weight of
1/2 atom of Magnesium.
1 atom of Magnesium weighs 24.3 grams.

Thus the gram equivalent of Magnesium is 24.3 / 2 grams ie 12.15 grams.
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What is the gram equivalent of Aluminium if you know that the Chloride is AlCl3 and the atomic weight of Aluminium is 27.0 g?

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