1. find the number of atoms present in 4g of helium..??
2. find the number of oxygen atoms present in 22g of co2..??
3. find the number of moles present in 51g of nh3..??
1) The molar mass that is the mass of 6.022 X 1023 atoms of helium is 4g.
Hence 1 mole of He = 4 g of He = 6.022 X 1023 atoms of He.
2) Molar mass of CO2 = 12 + 2(16) = 44 g
Thus
1 mole of CO2 contains = 2 moles of Oxygen atom
44 g of CO2 contains = 2 moles of oxygen atom
1g of CO2 contains = (2/44) moles of O atoms
22 g of CO2 contains = (2/44) x 22 moles of O = 1 mole of O atoms = 6.022 x 1023 atoms of oxygen
3) 1 mole of NH3 = 17g of NH3
No. of moles = given mass/molar mass
=51/17
=3 moles