The given percent composition of an organic compound is #48.76% "C"# and #8.04% "H"#. Its molecular mass is #"74 g/mol"#. What are its empirical and chemical formulas?

Question

Mateo Aguilar · Accepted Answer

Since the empirical formula mass is the same as the molecular mass, the empirical and molecular formulas are the same, #"C"_3"H"_6"O"_2"#.

Take a look at the comments. The given percent composition of an organic compound is #48.76% "C"# and #8.04% "H"#. The remaining #43.20%# is oxygen. Since the percentages add up to #"100%"#, you can assume that you have #"100 g"# of the substance. This allows you to convert percentages directly to mass in grams. Now you need to calculate the moles of each element by dividing its mass in the compound by its molar mass, which is its atomic weight in #"g/mol"#. #48.76 cancel"g C"xx(1"mol C")/(12.011cancel"g C")="4.0596 mol C"# #8.04 cancel"g H"xx(1"mol H")/(1.008cancel"g H")="7.9761 mol H"# #43.20cancel"g O"xx(1"mol O")/(15.999cancel"g O")="2.7002 mol O"# Find the Empirical Formula An empirical formula represents the lowest whole-number ratio of elements in a compound. To determine the mole ratios, divide the moles of each element by the lowest number of moles, #2.7002 "mol O"#. The mole ratios will give us the subscripts. #"C":##(4.0596cancel"mol")/(2.7002 cancel"mol")="1.5034# #"H":##(7.9761cancel"mol")/(2.7002 cancel"mol")="2.9539# #"O":##(2.7002cancel"mol")/(2.7002cancel"mol")="1.0000# The subscripts in an empirical formula indicate the lowest whole-number ratio of elements in a compound. Because the mole ratio of carbon is #1.5#, we need to multiply the mole ratios by #2# in order to get a whole-number ratio for all of the elements. #"C":##1.5034xx2=3.068~~3# #"H":##2.9539xx2=5.9078~~6# #"O":##1.0000xx2=2# The empirical formula is #"C"_3"H"_6"O"_2"#. The molar mass of each element multiplied by the sum of its subscripts yields the formula mass for the empirical formula. #(3xx12.011)+(6xx1.008)+(2xx15.999)=74.079~~74"g/mol"# Since the empirical formula mass is the same as the molecular mass, the empirical and molecular formulas are the same, #"C"_3"H"_6"O"_2"#.

Olivia Anton · Answer

undefined To find the empirical formula:
1. Convert the percentages to moles by assuming a 100 g sample.
2. Find the simplest whole number ratio of the elements.
3. Use this ratio to determine the empirical formula.

For carbon (C):
$48.76\% \, C$ → $48.76 \, g$ of C → $48.76 \, g / 12.01 \, g/mol$ = $4.06 \, mol \, C$

For hydrogen (H):
$8.04\% \, H$ → $8.04 \, g$ of H → $8.04 \, g / 1.01 \, g/mol$ = $7.96 \, mol \, H$

The simplest whole number ratio of C to H is approximately 1:2.

Therefore, the empirical formula is $CH_2$.

To find the molecular formula:
1. Calculate the molar mass of the empirical formula.
2. Divide the given molecular mass by the molar mass of the empirical formula to find the ratio.
3. Multiply the subscripts in the empirical formula by this ratio to get th