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An unknown compound is found to contain 40.0 percent carbon, 6.7 percent hydrogen and 53.3 percent oxygen with a molecular mass of 60.0 g/mol. what is the molecular formula of the unknown compound?

Respuesta :

McChuck
First act as if each percentage is mass, then divide by the element's molar mass.

[tex]C = \frac {40}{12.01} =3.331[/tex] 
[tex]H = \frac {6.7}{1.01}=6.634[/tex]
[tex]O = \frac {53.3}{16} = 3.331[/tex]

Then, out of all the solutions we must figure which one is the least. Continued by dividing each solution by the smallest solution. We can see that 3.331 is the least solution. Each answer should be rounded to a whole number, so they can become subscripts for the empirical formula.

[tex]C= \frac{3.331}{3.331}=1[/tex]
[tex]H= \frac{6.634}{3.331} = 1.992 = 2[/tex]
[tex]O= \frac{3.331}{3.331}=1[/tex]

The empirical formula is [tex]CH_2O[/tex]

Now we find the molar mass of the empirical formula and divide the molecular mass by the empirical formula mass. Finally round to a whole number.

Empirical Formula Mass: [tex]30.04g/mol[/tex]

[tex] \frac{60.0}{30.04}= 1.997 = 2[/tex]

Finally we multiply 2 by the Empirical Formula. That will give the molecular formula.

[tex]2 * CH_2O=C_2H_4O_2[/tex]

The answer is [tex]C_2H_4O_2[/tex]

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