Burning then sample of an organic compound with the weight of 0.00480 g it is afforded: 0.00703 g of the CO2 and 0.00283 g of the H2O, Determine the empirical formula of the compound which consists of hydrogen, carbon and oxygen?

1 Answer
Sep 22, 2016

Answer:

The empirical formula is #"CH"_2"O"#.

Explanation:

We can calculate the masses of #"C"# and #"H"# from the masses of their oxides (#"CO"_2# and #"H"_2"O"#).

#"Mass of C" = 7.03 color(red)(cancel(color(black)("mg CO"_2))) × "12.01 mg C"/(44.01 color(red)(cancel(color(black)("mg CO"_2)))) = "1.918 g C"#

#"Mass of H" = 0.283 color(red)(cancel(color(black)("mg H"_2"O"))) × "2.016 mg H"/(18.02 color(red)(cancel(color(black)("mg H"_2"O")))) = "0.3166 mg H"#

#"Mass of O" = "Mass of compound - mass of C - mass of O" = "4.80 mg - 1.918 mg - 0.3166 mg" = "2.565 mg"#

Now, we must convert these masses to moles and find their ratios.

From here on, I like to summarize the calculations in a table.

#"Element"color(white)(X) "Mass/mg"color(white)(X) "Millimoles"color(white)(m) "Ratio"color(white)(m)"Integers"#
#stackrel(—————————————————-———)(color(white)(ll)"C" color(white)(XXXmm)1.918 color(white)(mmm)0.1597 color(white)(Xlll)1color(white)(Xmmml)1#
#color(white)(ll)"H" color(white)(XXXXm)0.3166 color(white)(mml)0.3145 color(white)(mlll)1.969 color(white)(XXl)2#
#color(white)(ll)"O" color(white)(mmmml)color(white)(ll)2.565color(white)(mmll)0.1603color(white)(mm)1.004color(white)(mml)1#

The empirical formula is #"CH"_2"O"#.