Question

calculate the number of molecules in 50 grams of CaCO3

Answer 1

Calcium carbonate is CaCO3 so there is (in one mole) 40g of calcium because there would be one mole of that, 12g of carbon because there would be one mole of that, and 48g of oxygen because there are three moles of that.  

40+12+48 = 100  

so in one mole (which is 6.02x10^23 molecules) there is 100g of CaCO3  

there is 50g which would make it half a mole of CaCO3  

6.02x10^23 / 2 = 3.01x10^23  

so there would be 3.01x10^23 molecules of CaCO3  

the molar masses of the elements are obtained from a periodic table by the way  

Answer 2

Mole=mass/molecular mass

Here, molecular mass of CaCO3 is100 and mass is 50g

Therefore,mole of CaCO3=50/100=0.5

We know that mole(n)=no.of particles(N)/Avogadro number

Therefore,0.5=N/6.022×10^23

=3.011×10^23