Question

What mass of oxygen is needed for the complete combustion of 1.20×10−3 g of methane? Express your answer with the appropriate units

Answer 1

number of mole = (given mass)/(moplar mass)
molar mass of CH4 = 16 g/mol
number of mole of CH4 = (1.20*10^-3)/16
= (7.5*10^-5) mole

reaction taking place
CH4 + 2O2 --> CO2 + 2H2O
according to reaction
1 mole of CH4 react with 2 mole of O2
(7.5*10^-5) mole of CH4 react with (2*7.5*10^-5) mole of O2
so,
number of mole of O2 required = (15*10^-5) mole

molar mass of O2 = 32 g/mol
mass of O2 required = (number of mole of O2 required)*(molar mass of O2)
= (15*10^-5)*32
= (4.8*10^-3) g

Answer : (4.8*10^-3) g