Empirical and Molecular Formulas Quiz
Questions: 16 · 10 minutes
1. A compound has the empirical formula CH2, whose formula mass is approximately 14 g/mol. Which value could be the compound's molar mass?
20 g/mol
28.5 g/mol
35 g/mol
42 g/mol
2. A compound has the empirical formula NO2 and a molar mass of approximately 92 g/mol. What is its molecular formula?
NO2
N2O2
N2O4
N4O2
3. A compound has the empirical formula C2H3O, with an empirical formula mass of 43 g/mol. Its molar mass is 86 g/mol. What is its molecular formula?
C2H3O
C4H6O2
C6H9O3
C4H3O2
4. A sample contains 0.40 mol of carbon atoms and 1.00 mol of hydrogen atoms. What is the empirical formula?
CH2
C2H4
CH5
C2H5
5. Which compound has the same empirical formula as C2H4?
C3H6
C3H8
CH4
C2H2
6. How does the molar mass of a molecular formula compare with the mass of its corresponding empirical formula?
It is always equal to the empirical formula mass
It is a positive integer multiple of the empirical formula mass
It is the empirical formula mass divided by an integer
It differs from the empirical formula mass only by the mass of hydrogen
7. After dividing mole amounts by the smallest value, a student obtains the ratio C:H = 1:1.5. What should the student do next to obtain whole-number subscripts?
Round 1.5 down to 1
Round 1.5 up to 2
Multiply both values by 2
Divide both values by 2
8. Analysis gives 0.20 mol of carbon, 0.30 mol of hydrogen, and 0.10 mol of oxygen. What is the empirical formula?
C2H3O
C2H3O2
CH3O
C2H6O
9. A compound has the empirical formula CH2O and a molar mass of 180 g/mol. The empirical formula mass is approximately 30 g/mol. What is its molecular formula?
C3H6O3
C6H12O6
C2H4O2
CH2O
10. Why is NaCl normally described using a formula unit rather than a molecular formula?
Its sodium and chlorine atoms are present in equal masses
Its subscripts cannot be reduced to whole numbers
It forms an extended ionic lattice rather than discrete NaCl molecules
Its composition changes whenever it dissolves in water
11. A hypothetical compound has the empirical formula P2O5. Which formula could not be a corresponding molecular formula?
P4O5
P2O5
P4O10
P6O15
12. What does an empirical formula represent?
The simplest whole-number ratio of atoms of each element in a compound
The actual number of atoms of each element in one molecule
The arrangement of atoms and bonds within a molecule
The percentage by mass of each isotope in a sample
13. A chemist determines a compound's exact elemental mass percentages but has no molar-mass measurement. What can generally be determined from these data alone?
The molecular formula only
Both the molecular and structural formulas
The molecular formula, but not the empirical formula
The empirical formula, but not necessarily the molecular formula
14. What is the empirical formula of C6H12O6?
C6H12O6
C3H6O3
CH2O
C2H4O2
15. A compound is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Assuming a 100 g sample, what is its empirical formula?
CH3O
C2H4O2
CHO
CH2O
16. Which statement correctly relates a compound's molecular formula to its empirical formula?
The empirical formula is always an integer multiple of the molecular formula
The molecular formula is an integer multiple of the empirical formula
The two formulas must always be identical
The molecular formula is found by reducing the empirical formula's subscripts