(i) What is the mass of one atom of hydrogen? (atomic mass of hydrogen = 1 u) (ii) How many `NH_4` ions are present in 1.5 moles of `(NH_4)_3PO_4`?

Explanation

(i) Mass of `6.022 xx 10^23` hydrogen atoms = 1 g
Mass of 1 hydrogen atom = `(1 g)/(6.022 xx 10^(23)) = 1.66 xx 10^(-24) g = 1.66 xx 10^(-27) kg`
Thus, Mass of one hydrogen atom = `1.66 xx 10^(-24)` g
`= 1.66 xx 10^(-27)` kg
(ii) Number of `(NH_4)_3PO_4` molecules `= 1.5 xx 6.022 xx 10^23`
One molecule of `(NH_4)3PO_4` contains 3 `NH_4` ions.
Hence, total number of `NH_4` ions
`= 3 xx 1.5 xx 6.022 xx 10^23 = 27.1 xx 10^23`