A hardware store clerk is told to weigh one pound of machine
bolts for a customer, and also to weigh approximately enough hexagonal
nuts to go with them. He finds that a hex nut weighs 0.40 as much
as a machine bolt of the type requested. How many nuts should he
include with the order? Answer. He should include 0.40 X 1 pound = 0.40 pound of
Such a procedure would be good enough for most real situations,
and a lot easier and faster than sitting down and counting individual
pieces. This is exactly what the chemist does with molecules.
Example. A chemist wants to make as much methane, ,
as he can from 100 g of carbon. How much hydrogen will be required?
Solution. The atomic weight of hydrogen is 1.008 amu, and
that of carbon is 12.011 amu. Four hydrogen atoms are required for
each carbon atom, so 4x1.008 amu = 4.032 amu of hydrogen will be
needed for each 12.011 amu of carbon. The relative weights of hydrogen
and carbon will be 4.032 units of hydrogen to 12.011 units of carbon,
whatever the weighing units chosen. The problem was expressed in