Calculate the number of atoms in each of the following : (i) 52 moles of He (ii) 52 amu of He (iii) 52 grams of He.

Calculate the number of atoms in each of the following : (i) 52 moles

1.	Calculate the number of atoms in each of the following : (i) 52 moles of He (ii) 52 amu of He (iii) 52 grams of He.
Answer» Solution :(i) HELIUM is monoatomic in nature. One mole of any substance has `6.022 XX 10^(23)`molecules. .Number of molecules in 52 moles of He `=52 xx 6.022 xx 10^(23) = 3.131 xx 10^(25)` SINCE, helium is monoatomic, i.e., its one molecule is composed of one ATOM, the number of atoms present in 52 moles of He = `3.131 xx 10^(25)` . Hence, 52 moles of He contain `3.131 xx 10^(25)`atoms. (ii) The atomic mass of He is 4.003 amu. This means that the mass of one atom of He is 4.003 amu. `therefore` Number of atoms contained in 52 amu of He `=52/(4.003) = 12.99 = 13` Hence, 52 amu of He contain 13 atoms. (iii) The gram atomic mass of He = 4.003 g.This means that 4.003 g of He contain `6.022 xx 10^23` atoms. `therefore` Number of atoms present in 52 g of He `=(6.022 xx 10^(23))/(4.003)xx 52 = 7.823 xx 10^(24)` Hence, 52 g of He possesx `7.832 xx 10^(24)` atoms.