(iv) Parts per million: When a solute is present in trace quantities, it
is convenient to express concentration in parts per million (ppm)
and is defined as:
Parts per million =
 
6
Number of parts of the component
×10
Total number of parts of all components of the solution
(1 3)
As in the case of percentage, concentration in parts per million can
also be expressed as mass to mass, volume to volume and mass to
volume A litre of sea water (which weighs 1030 g) contains about
6 × 10
–3 g of dissolved oxygen (O2) Such a small concentration is
also expressed as 5