m[tex]_{C10H18}[/tex]=10*12u+18*1u=138u
m[tex]_{C10}[/tex]=10*12u=120u
138 - 100%
120 - x%
x=[tex]\frac{100*120}{138} =86.96[/tex]
Zawartość procentowa węgla w C10H18 wynosi 86.96%