Name:
Period:
Molecular Formula – Level 1
Write the molecular formulas for the following compounds. Show all your work.
1.
A compound has the following percentage composition: 26.7% carbon; 2.2% hydrogen; 71.1% oxygen. The actual mass of this
compound is 90.04 grams. What is the compound’s true formula?
Step 1 :
Step 2 :
26.70 g C
 2.220 moles C
12.01 g mole
C
2.220
1
2.190
Step 3: CHO2
2.200 g H
 2.190 moles H
1.008 g mole
H
2.190
1
2.190
71.10 g O
 4.440 moles O
16.00 g mole
O
4.440
2
2.190
Step 4:
(1mole )(12.01 g/mole) + (1 mole)(1.008 g/mole) + (2 mole) (16.00 g/mole) = 45.02 g
Step 5:
90.04 grams / 45.02 grams = 2 => We actually have TWICE as much!
Step 6:
2 (CHO2) =
C2H2O4 – this is the molecular formula
2.
A certain compound was analyzed and found to have the following composition: 54.60% carbon; 9.00 % hydrogen; 36.4% oxygen.
The actual mass of the compound is 176 g. What is the molecular formula of the compound?
3.
The percentage composition of ethane gas is 80.0% carbon and 20.0% hydrogen. The molecular weight for ethane is 30.0 g/mole.
What is the correct formula for this compound?
1
4.
Analysis of a compound shows that it consists of 24.3% carbon, 4.1% hydrogen, and 71.6% chlorine. The actual mass of the
compound is determined to be 98.8 grams. What molecular formula corresponds to these data?
5.
An unknown compound is analyzed and found to consist of 49.0% carbon, 2.7% hydrogen, and 48.2% chlorine. Boiling point data
suggest that the actual mass of the sample is 150 grams. What molecular formula would you predict for this compound?
6.
A gaseous compound is found to have the following composition: 30.5% nitrogen and 69.5% oxygen. The actual mass of the gas
sample is found to be 91.8 grams. What molecular formula corresponds to these data?
2