Question

Adenine had a molecular mass of 135.1 and consist of 44.45%C, 3.13%H and 52.82%N by mass. Determine its molecular formular

Answer 1

• The molecular mass of carbon in adenine can be calculated by multiplying the molecular mass of adenine by the percentage of carbon:

M(C) = 135.1(g/mol)•(44.45%/100%) = 60.05 g/mol $\to$ then we can calculate the number of the carbon in adenine:

$N$ (of carbon's atoms) = $M$ (summary mass of all carbon's atoms)$/M$ (mass of one carbon's atom) = 60.05(g/mol)/12.01(g/mol) = 5

• Then, similarly, we first calculate the molecular masses of hydrogen and nitrogen, and then the number of their atoms in adenine:

M(H) = 135.1(g/mol)•(3.13%/100%) = 4.5 g/mol $\to$ $N$ (of hydrogen's atoms) = $M$ (summary mass of all hydrogen's atoms)/$M$(mass of one hydrogen's atom) = 4.5(g/mol)/1(g/mol) = 5 (in rounding)

M(N) = 135.1(g/mol)•(52.82%/100%) = 71.36(g/mol) $\to$ $N$ (of nitrogen's atoms) = $M$ (summary mass of all nitrogen's atoms)/$M$(mass of one nitrogen's atom) = 71.36(g/mol)/14(g/mol) = 5

Answer: the molecular formula of adenine is C₅H₅N₅