Convert into moles :
(a) 12 g of oxygen gas
(b) 20 g of water
(c ) 22 g of carbon dioxide
(Atomic masses : `O = 16 u, H = 1 u` and `C = 12 u`)

Explanation

(a) Oxygen gas consists of `O_(2)` molecules . So, molecular mass of oxygen gas `(O_(2)) = 16 xx 2 = 32 u`
Now, 1 mole of oxygen gas = Molecular mass of ox ygen in grams
`= 32 g`
If 32 g of oxygen gas `= 1` mole
Then 12 g of oxygen gas `= 1/32 xx 12` mole
`= 0.375` mole
(b) Water consists of `H_(2)O` molecular mass of water `(H_(2)O) = 1 xx 2 + 16 = 18 u`.
Now, 1 mole of water = Molecular mass of water in grams
` = 18 g`
If 18 g of water `= 1` mole
Then 20 g of water = `1/18 xx 20` mole
`= 1.11` mole
(c ) Carbon dioxide consists of `CO_(2)` molecules. So, molecular mass of carbon dioxide `(CO_(2)) = 12 + 1 xx 2`
` = 12 + 32 = 44 u`.
Now, 1 mole of carbon dioxide = Molecular mass of carbon dioxide in grams
`= 44 g`
If 44 g of carbon dioxide = 1 mole
Then, 22 g of carbon dioxide `= 1/44 xx 22` mole
`= 1/2` mole
`= 0.5` mole