Answer :

17.6% oxygen
% mass = molar mass of part over molar mass of whole,
molar mass of oxygen is 16
molar mass of carbon is 12
molar mass of hydrogen is 1
so (16) / (16+12*6+3) = 16/91 = 17.58%

Answer : The percent by mass of oxygen in propanal is, 27.58 %

Solution : Given,

Molar mass of carbon = 12 g/mole

Molar mass of hydrogen = 1 g/mole

Molar mass of oxygen = 16 g/mole

First we have to calculate the molar mass of propanal, [tex]CH_3CH_2CHO[/tex]

Molar mass of propanal, [tex]CH_3CH_2CHO[/tex] = [tex]3(12)+6(1)+16=58g/mole[/tex]

Now we have to calculate the percent by mass of oxygen in propanal.

[tex]\text{Percent by mass of oxygen}=\frac{\text{Mass of oxygen}}{\text{Mass of propanal}}\times 100=\frac{16}{58}\times 100=27.58\%[/tex]

Therefore, the percent by mass of oxygen in propanal is, 27.58 %