Calculate the number of moles and molecules of urea present in 5.6 g of urea.

Explanation

Mass of urea = 5.6 g Molecular mass of urea, `NH_2CONH_2` = 2 (average atomic mass of N) + 4 (average atomic mass of H) + 1(average atomic mass of C) + 1(average atomic mass of O)
`= 2 xx 14 u +1 xx 12 u +4 xx1 u + 1 xx 16 u` = 60 u
`therefore `molar mass of urea = 60 g `"mol"^(-1)`
Number of moles ` = (5.6)/(60 g"mol"^(-1)) = 0.0933 `mol
Number of molecules = Number of moles x Avogadro.s constant
Number of molecules of urea
`= 0.0933 xx 6.022 xx 10^23` molecules/mol
` = 0.5618 xx 10^23` molecules
` = 5.618 xx 10^22` molecules