Molar mass percentage composition empirical and molecular formulae - Question Bank

1. What is the molar mass of carbon dioxide (CO2)? (Atomic masses: C = 12, O = 16)
A) 28 g/mol
B) 32 g/mol
C) 44 g/mol
D) 50 g/mol
2. If the empirical formula of a compound is C5H10O and its molar mass is 100 g/mol, what is its molecular formula?
A) C5H10O
B) C10H20O2
C) C5H10O2
D) C10H10O
3. A compound contains 5.88% hydrogen, 70.59% carbon, and 23.53% oxygen by mass. What is its empirical formula?
A) C2H3O
B) C3H4O
C) C3H5O
D) C4H5O
4. What is the percentage by mass of hydrogen in methane (CH4)? (Atomic masses: C = 12, H = 1)
A) 6.25%
B) 12.5%
C) 25.0%
D) 50.0%
5. The molar mass of a compound is 128 g/mol. Its empirical formula is CH2. What is its molecular formula?
A) CH2
B) C2H4
C) C4H8
D) C8H16
6. A compound has an empirical formula of N2O4. What is its simplest whole-number ratio of atoms?
A) N2O4
B) NO2
C) N3O4
D) N2O3
7. What is the percentage by mass of carbon in glucose (C6H12O6)? (Atomic masses: C = 12, H = 1, O = 16)
A) 20.0%
B) 40.0%
C) 60.0%
D) 80.0%
8. If the empirical formula of a compound is C3H4 and its molar mass is 80 g/mol, what is its molecular formula?
A) C3H4
B) C6H8
C) C3H8
D) C4H4
9. A compound contains 85.7% carbon and 14.3% hydrogen by mass. What is its empirical formula?
A) CH
B) CH2
C) C2H
D) C2H3
10. What is the molar mass of ethanol (C2H5OH)? (Atomic masses: C = 12, H = 1, O = 16)
A) 32 g/mol
B) 46 g/mol
C) 50 g/mol
D) 60 g/mol
11. The empirical formula of a compound is C2H6O. If its molar mass is 46 g/mol, what is its molecular formula?
A) C2H6O
B) C4H12O2
C) CH3OH
D) C2H5OH
12. A compound has an empirical formula of CH2Cl. If its molar mass is 99 g/mol, what is its molecular formula?
A) CH2Cl
B) C2H4Cl2
C) C3H6Cl3
D) C4H8Cl4
13. What is the percentage by mass of iron in iron(III) oxide (Fe2O3)? (Atomic masses: Fe = 56, O = 16)
A) 40.0%
B) 50.0%
C) 60.0%
D) 70.0%
14. If the empirical formula of a compound is C3H6O2 and its molar mass is 118 g/mol, what is its molecular formula?
A) C3H6O2
B) C6H12O4
C) C3H6O4
D) C4H8O2
15. What is the molar mass of potassium carbonate (K2CO3)? (Atomic masses: K = 39, C = 12, O = 16)
A) 100 g/mol
B) 110 g/mol
C) 120 g/mol
D) 138 g/mol
16. A compound is found to contain 47.06% potassium, 14.47% carbon, and 38.47% oxygen by mass. What is its empirical formula?
A) K2CO3
B) KCO2
C) K2C2O3
D) KC2O3
17. The empirical formula of a compound is CH2. If its molar mass is 42 g/mol, what is its molecular formula?
A) CH2
B) C2H4
C) C3H6
D) C4H8
18. What is the percentage by mass of sulfur in sulfur dioxide (SO2)? (Atomic masses: S = 32, O = 16)
A) 33.3%
B) 50.0%
C) 66.7%
D) 75.0%
19. If the empirical formula of a compound is C2H5 and its molar mass is 58 g/mol, what is its molecular formula?
A) C2H5
B) C4H10
C) C6H15
D) C3H7.5
20. A compound contains 60% carbon, 8% hydrogen, and 32% oxygen by mass. What is its empirical formula?
A) C3H4O
B) C3H5O
C) C2H3O
D) C4H6O
21. Which of the following is the molar mass of water (H2O)? (Atomic masses: H = 1, O = 16)
A) 17 g/mol
B) 18 g/mol
C) 19 g/mol
D) 20 g/mol
22. A compound has an empirical formula of P2O5. If its molar mass is 284 g/mol, what is its molecular formula?
A) P2O5
B) P4O10
C) P6O15
D) P8O20
23. What is the percentage by mass of nitrogen in ammonia (NH3)? (Atomic masses: N = 14, H = 1)
A) 14%
B) 28%
C) 47%
D) 82%
24. The empirical formula of a carbohydrate is CH2O. If the molar mass of the carbohydrate is 180 g/mol, how many carbon atoms are there in one molecule of the carbohydrate?
A) 1
B) 2
C) 6
D) 12
25. A compound contains 75% carbon and 25% hydrogen by mass. If its molar mass is 16 g/mol, what is its molecular formula?
A) CH
B) CH2
C) C2H2
D) CH4
26. What is the molar mass of methane (CH4)? (Atomic masses: C = 12, H = 1)
A) 10 g/mol
B) 12 g/mol
C) 16 g/mol
D) 20 g/mol
27. If the percentage composition of a compound is 10% Hydrogen and 90% Carbon by mass, what is its empirical formula?
A) CH
B) CH2
C) C2H
D) C3H
28. A compound has the molecular formula C3H8. What is its empirical formula?
A) C3H8
B) C3H4
C) C2H4
D) CH
29. What is the molar mass of calcium carbonate (CaCO3)? (Atomic masses: Ca = 40, C = 12, O = 16)
A) 80 g/mol
B) 100 g/mol
C) 120 g/mol
D) 140 g/mol
30. The empirical formula of a compound is C4H8O2. If its molar mass is 88 g/mol, what is its molecular formula?
A) C4H8O2
B) C2H4O
C) C8H16O4
D) C4H8O
31. If 10 grams of a compound contain 4 grams of element A and 6 grams of element B, and the atomic mass of A is 10 amu and B is 15 amu, what is the empirical formula?
A) AB
B) A2B3
C) A3B2
D) A3B
32. What is the percentage by mass of oxygen in pure sulfuric acid (H2SO4)?
A) 16.3%
B) 32.7%
C) 51.0%
D) 65.3%
33. The molar mass of a compound is 78 g/mol. Its empirical formula is CH. What is its molecular formula?
A) CH
B) C2H2
C) C6H6
D) C3H3
34. A sample of a compound contains 8.33 g of carbon, 1.39 g of hydrogen, and 11.08 g of oxygen. What is the empirical formula of this compound?
A) CH2O
B) C2H4O2
C) CHO
D) C3H6O3
35. Which of the following compounds has the same empirical formula as its molecular formula?
A) Ethane (C2H6)
B) Ethene (C2H4)
C) Water (H2O)
D) Benzene (C6H6)
36. The percentage composition of an oxide of nitrogen is 30.4% nitrogen. What is its empirical formula?
A) NO
B) NO2
C) N2O
D) N2O4
37. If the empirical formula mass of a compound is 29 g/mol and its molar mass is 58 g/mol, what is the value of 'n' in the relation Molecular Formula = (Empirical Formula)n?
A) 1
B) 2
C) 3
D) 4
38. What is the molar mass of the empirical formula CH2Cl2?
A) 50.5 g/mol
B) 84.5 g/mol
C) 49.5 g/mol
D) 99 g/mol
39. A compound has 24.24% carbon, 4.04% hydrogen, and 71.72% chlorine by mass. What is its empirical formula?
A) CH2Cl
B) CHCl
C) CCl2
D) CH3Cl
40. Which of the following statements about empirical and molecular formulas is INCORRECT?
A) The molecular formula is always a whole-number multiple of the empirical formula.
B) The empirical formula represents the actual number of atoms in a molecule.
C) Both formulas show the types of elements present in a compound.
D) The empirical formula is the simplest ratio of atoms.
41. If a compound has an empirical formula of C3H7 and a molar mass of 86 g/mol, what is its molecular formula?
A) C3H7
B) C6H14
C) C9H21
D) C3H7O
42. The empirical formula of glucose is CH2O. What is the molar mass of glucose if its molecular formula is C6H12O6?
A) 30 g/mol
B) 60 g/mol
C) 180 g/mol
D) 360 g/mol
43. What is the molar mass of a compound if its empirical formula is CH and its molar mass is twice the molar mass of its empirical formula?
A) 13 g/mol
B) 26 g/mol
C) 14 g/mol
D) 28 g/mol
44. A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. If its molar mass is 180 g/mol, what is its molecular formula?
A) CH2O
B) C2H4O2
C) C6H12O6
D) C3H6O3
45. The percentage composition of a compound is determined by:
A) Dividing the mass of the element by the total mass of the compound and multiplying by 100.
B) Dividing the number of moles of the element by the total number of moles of the compound and multiplying by 100.
C) Dividing the atomic mass of the element by the molecular mass of the compound and multiplying by 100.
D) Dividing the mass of the element by the atomic mass of the element and multiplying by 100.
46. If the empirical formula of a compound is CH2O and its molar mass is 180 g/mol, what is its molecular formula?
A) CH2O
B) C2H4O2
C) C6H12O6
D) C3H6O3
47. What information does the molecular formula provide that the empirical formula does not?
A) The exact number of atoms of each element in a molecule.
B) The simplest ratio of atoms of each element in a compound.
C) The type of elements present in the compound.
D) The relative number of atoms of each element.
48. Which of the following represents the simplest whole-number ratio of atoms of each element in a compound?
A) Molecular formula
B) Empirical formula
C) Structural formula
D) Condensed formula
49. If a compound has the molecular formula C2H6, what is its empirical formula?
A) C2H6
B) CH3
C) C3H8
D) CH2
50. What is the definition of molar mass percentage composition of a compound?
A) The percentage by mass of each element in a compound.
B) The ratio of the molar mass of an element to the molar mass of the compound, multiplied by 100.
C) The total mass of all atoms in one mole of a compound.
D) The number of moles of each element in one mole of a compound.
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