CALCULATIONS
BASED ON FORMULAE
7.2 - Mole
Concept
Count
by weighing
This is similar to buying nails in a hardware store. Although
each nail does not have the same mass, it is too time consuming to count the
number nails at the check out. So, nails are usually purchased by weighing.
Chemistry is more exact than buying nail from a hardware store because atoms
of the same types have the EXACT same mass.
- 1 carbon atom weighs 12.011 amu
(section 3.5), so 1 mole carbon
atoms (or 6.022 x 1023
carbon atoms) has an equivalent mass of 12.011
grams. So, instead of counting 6.022 x 1023
carbon atoms, we know that if we have a sample of carbon atoms that
weighs 12.011 grams, there must be 6.022 x 1023
carbon atoms in the sample.
- 1 hydrogen atom weighs 1.008 amu,
so 1 mole hydrogen atoms (or 6.022
x 1023 hydrogen atoms) has an equivalent mass of
1.008
grams. So, instead of counting 6.022 x 1023
hydrogen atoms, we know that if we have a sample of hyrogen atoms that
weighs 1.008 grams, there must be 6.022 x 1023
hydrogen atoms in the sample.
- 1 oxygen atom weighs 15.999 amu, so 1 mole of oxygen atoms (or 6.022
x 1023 oxygen atoms) has an equivalent mass of 15.999
grams. So, instead of counting 6.022 x 1023
oxygen atoms, we know that if we have a sample of oxygen atoms that
weighs 15.999 grams, there must be 6.022 x 1023
oxygen atoms in the sample.
