A compound is composed of 19.998% carbon, 3.331% hydrogen, 23.320% nitrogen, and 53.302% Oxygen. Its molar is 120.07 gram/mole. What are the empirical and molecular formulas?
There is a good rote way to do these:
19.998% carbon, 3.331% hydrogen, 23.320% nitrogen, and 53.302% oxygen
Assume 100 g
19.998g carbon, 3.331g hydrogen, 23.320g nitrogen, and 53.302g oxygen
divide by molar mass of each
19.998/12 carbon, 3.331/1 hydrogen, 23.320/14 nitrogen, and 53.302/16 oxygen
1.667 mole carbon, 3.331 mole hydrogen, 1.667 mole nitrogen, and 3.331 mole oxygen
divide by smallest to get ratio
1 mole carbon, 2 mole hydrogen, 1 mole nitrogen, and 2 mole oxygen
so empirical is
CH2NO2
molar mass of which is 60 g mole^-1
so molecular formula is
C2H4N2O4
1,1-dinitroethane ???
To find the empirical and molecular formulas, follow these steps:
Step 1: Convert the percentages to grams.
- Assume we have 100g of the compound.
- Carbon: 19.998g
- Hydrogen: 3.331g
- Nitrogen: 23.320g
- Oxygen: 53.302g
Step 2: Calculate the number of moles of each element.
- Divide the mass of each element by its molar mass:
- Carbon: 19.998g / 12.01g/mol = 1.666 moles
- Hydrogen: 3.331g / 1.008g/mol = 3.305 moles
- Nitrogen: 23.320g / 14.01g/mol = 1.665 moles
- Oxygen: 53.302g / 16.00g/mol = 3.331 moles
Step 3: Determine the empirical formula.
- Find the lowest ratio of moles between the elements. In this case, the ratio is approximately 1:2:1:2.
- Multiply the subscripts by a common factor (in this case, 2) to obtain whole number ratios. So the empirical formula is C2H4N2O4.
Step 4: Calculate the empirical formula mass.
- Add up the molar masses of the elements in the empirical formula:
- C2H4N2O4:
- (2 * 12.01) + (4 * 1.008) + (2 * 14.01) + (4 * 16.00) = 56.06g/mol
Step 5: Calculate the molecular formula.
- Divide the molar mass of the compound given (120.07g/mol) by the empirical formula mass (56.06g/mol). The result is approximately 2.14.
- Multiply the subscripts in the empirical formula by this factor: C4H8N4O8.
So, the empirical formula is C2H4N2O4, and the molecular formula is C4H8N4O8.