Question

which amongst the following has more number of atoms and how much? (given atomic mass of na =23u,ca =40u)a) 11.5 g of sodium b) 15.0 of calcium​

Answer 1

Hey, to simply solve this question we will calculate number of moles in each case, compound having more number of moles will have more number of atoms.

a) No. of moles = Mass of sodium / Molecular mass of sodium

                         = 11.5 / 23 = 0.5 moles

b) No. of moles = Mass of calcium/ Molecular mass of calcium

                         = 15 / 40    = 0.375 moles

In, b)  number of atoms = 0.375 x 6.022 x 10^23 = 2.26 x 10^23 atoms

In, a) atoms = 0.5 x 6.022 x 10^23 = 3.011 x 10^23 atoms

Thus, Sodium has more number of atoms

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Answer 2

23 g of Na =1 mole  

11.5 g of Na = 11.5/23 mole

Now, 1 mole of Na contains

= 6.022 x 10^23 atoms

11.5/23 mole of Na contains

= 6.022x10^23 x 11.5/ 23mole

= 3.011 x 10^23 atoms

40 g of Ca =1 mole

15 g of Ca = 15/40 moles

Now, 1 mole of Ca contains

= 6.022 x 10^23 atoms

15/40 mole of Ca contains

= 6.022 x 10^23 x 15/40

= 2.258 x 10^23 atoms

Na has more number of atoms.