mass
'no magic to the mole'
amount
molar mass
concentration
solution volume
gas volume
molar gas volume
Avogadro
constant, L
number of
entities, N
Now try the following question.
B2. RELATIVE MASSES OF ATOMS, MOLECULES & FORMULA UNITS
2.1 THE KILOGRAM
The mass of any object expressed in any unit is measured relative to some STANDARD,
e.g., until just recently, the universal standard of mass was a block of Pt-Ir alloy, the
Formerly the global standard for the exact mass of 1 kg, the IPK is kept under lock and key at Saint-Cloud, Sèvres, Paris (FR).
standard kilogram (IPK - International Prototype Kilogram), kept under carefully controlled conditions in a glass case at Sèvres,(FR).
That this block of alloy is slowly shrinking was just one of the reasons why, in 2018, BIPM re-defined the kilogram in terms of a now fixed numerical value of the Planck constant, which is itself linked by updated definitions of the second and the metre based on invariable, atomic-scale properties.
In the everyday arena of a greengrocers, however, one buys three kilograms of potatoes: this is three times the mass of the standard kilogram and there are two different but nonetheless equivalent ways of expressing these:
‘the mass of the potatoes is 3 kg’;
‘on the kilogram scale the relative mass of the potatoes is 3’.
