Question

what is the mass of a billion (1*10⁹)molecules of carbon dioxide?

how many moles of oxygen atoms are there in 6.84g of Al₂(SO₄)₃?

Answer 1

1.

1 mole of any compound has 6.023*10²³ molecules

=> number of moles for 10⁹ molecules of CO₂ = 10⁹/(6.023*10²³) moles

Molecular mass of CO₂ = 12+16*2 = 44 gm/mole

=> mass of 10⁹ molecules of CO₂ = 44*[10⁹/(6.023*10²³)] = 0.778 gm

2.

molecular mass of Al₂(SO₄)₃ = 2*27 +3*32 + 12*16 = 342 gm/mole

=> number of moles for 6.84 gm of Al₂(SO₄)₃ = 6.84/342 = 0.02 moles

number of moles of O atoms in 1 mole of Al₂(SO₄)₃ = 12

=> number of moles of O atoms in 6.84g of Al₂(SO₄)₃ = 12*0.02 = 2.4 moles