The idea of #"equivalence"# is fundamental to the concept of stoichiometry... Now it is a fact that hydrogen as the gaseous ATOM has a molar mass of #1*g*mol^-1#. Why do we quote it per mole....? Because the mole is a convenient unit of measurement on which to base our calculations....
And one mole of #""^12C# atoms has a mass of #12*g#. The mole is thus the link between the sub-micro world of atoms and molecules, the which we cannot see, but whose presence we can infer, with the macro world of grams, and litres, and kilograms, the which we can measure by some means in the laboratory.
The following is taken from a prior answer on the mole concept....
Just as a comment, many students seem to have a conceptual difficulty with the mole. And try as we might, it is difficult to overcome.....
Now perhaps if we conceive of the mole as just another number, like a 100 or 10, or, even better, a dozen, we may address this conceptual difficulty.
As far as I know, a #"dozen"# is a convenient, and natural counting number, because we can use our thumb to number the tips and finger joints of the same hand.....
You could think of a mole as another collective number such as the dozen, except #"1 mole"-=6.02214xx10^23#.
Why should we use such an absurdly large number? Well, if I have #6.02214xx10^23# individual #""^1H# atoms, I have a mass of #1*g# precisely. And thus the mole is the link between the micro world of atoms and molecules, the which we cannot see, but whose existence we can infer, with the macro world of grams, litres, and kilograms, that which we can weigh out or measure in a laboratory. And if you learn anything in chemistry, this concept of chemical equivalence is the most important thing to learn.
And in exam, you are given a Table that conveniently lists the molar mass of each and every known element.
