What is the mass of :
(a) `0.2` mole of oxygen atoms?
(b) `0.5` mole of water molecules?

Explanation

(a) The atomic mass of oxygen (O) is `6u` So, the mass of 1 mole of oxygen atoms will be 16 grams.
Now, 1 mole of oxygen atoms `= 16 g`
So, `0.2` mole of oxygen atoms `= 16 xx 0.2 g`
`= 3.2 g`
(b) The molecular mass of water `(H_(2)O)` is `18 u`, so the mass of 1 mole of water molecules is 18 grams ,
Now, 1 mole of water molecules `= 18 g`
so, `0.5` mole of water molecules ` = 18 xx 0.5 g`
`= 9 g`