Question

1.Calculate mass of 2.5 gram atoms of magnesium
2. Calculate the mass of 0.72 gram molecule of CO2
In first question we are multiplying whereas in 2nd we are dividing why?? Why we are not multiplying same in 2nd

Answer 1

mass of one atom of mg= 24 amu or 24 grams of 1 mole of mg
so 24*2.5=60 g
in this we are multiplying as we want 2.5 times of the mass of one magnesium atom

(2) molecular mass of co2 in grams= 12*1+16*2= 12+32=44g
mass of 0.72 molecules =44*0.72=31.68g
in this we are not dividing but multiplying but the answer is less than the original mass because we are taking out the mass of less than one co2 molecule