Questions on Empirical Formula
Multiple-Choice Questions: Empirical Formula
🔹 Basic Understanding
1. What does the empirical formula of a compound represent?
A) The mass of each element in a compound
B) The arrangement of atoms in the molecule
C) The simplest whole-number ratio of atoms of each element
D) The volume of one mole of gas
E) The percentage composition of elements
2. Which of the following is an empirical formula?
A) C₂H₆
B) C₆H₁₂O₆
C) CH₄
D) C₄H₁₀
E) C₂H₄O₂
3. What is the empirical formula of C₄H₈?
A) CH₂
B) C₂H₄
C) C₄H₈
D) CH₄
E) C₃H₆
4. What is the empirical formula of glucose (C₆H₁₂O₆)?
A) CH₂O
B) C₂H₄O₂
C) C₃H₆O₃
D) CHO
E) C₆H₁₂O₆
5. Which compound has the same molecular and empirical formula?
A) H₂O₂
B) C₂H₆
C) C₄H₈O₄
D) CH₄
E) C₆H₆
🔹 Identification and Calculation
6. The empirical formula of a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen is:
A) C₂H₄O₂
B) CH₂O
C) C₂H₆O
D) CHO
E) C₂H₂O₂
7. If the molecular formula of a compound is C₈H₁₈, what is its empirical formula?
A) CH₄
B) C₄H₉
C) C₂H₅
D) C₈H₁₈
E) C₃H₇
8. What is the empirical formula of H₂O₂ (hydrogen peroxide)?
A) H₂O₂
B) HO
C) H₂O
D) H₃O
E) H₄O₂
9. Which of the following is NOT an empirical formula?
A) NH₃
B) CH₄
C) C₂H₂
D) CH
E) H₂O
10. What is the empirical formula of C₆H₆?
A) CH
B) C₃H₃
C) C₆H₆
D) CH₂
E) C₂H₂
🔹 Applied Examples
11. A compound has a molecular formula of C₄H₁₀. What is its empirical formula?
A) C₄H₁₀
B) C₂H₅
C) CH₅
D) C₂H₂
E) C₃H₇
12. Which formula represents the simplest ratio of atoms?
A) C₆H₁₂
B) C₂H₆O
C) CH₃
D) CH₂
E) CH
13. Which of these formulas is already in empirical form?
A) C₄H₈
B) C₂H₄
C) CH₂
D) C₆H₁₂
E) C₃H₆
14. What is the empirical formula of a compound that contains 24g of carbon and 4g of hydrogen?
A) CH
B) C₂H
C) CH₂
D) C₃H₈
E) C₂H₄
15. A compound has 85.7% carbon and 14.3% hydrogen. What is the empirical formula?
A) CH
B) CH₂
C) CH₄
D) C₂H₆
E) C₃H₈
🔹 Theory and Practice
16. Which of these steps is NOT required to calculate an empirical formula?
A) Convert mass to moles
B) Find the molecular mass
C) Divide all mole values by the smallest mole value
D) Round or multiply to get whole numbers
E) Determine percent composition
17. The empirical formula is most useful in:
A) Naming elements
B) Balancing redox reactions
C) Determining simplest atomic ratios
D) Determining temperature
E) Identifying isotopes
18. Which formula is NOT in empirical form?
A) H₂O
B) CO₂
C) C₆H₁₂O₆
D) CH
E) NH₃
19. A compound contains 70% iron and 30% oxygen. What is the empirical formula?
A) FeO
B) Fe₂O₃
C) Fe₃O₄
D) FeO₂
E) Fe₄O₃
20. The empirical formula of ethyne (C₂H₂) is:
A) CH
B) C₂H₂
C) CH₂
D) C₂H₄
E) C₄H₈
Answers with Explanations
1. C – The empirical formula shows the simplest ratio of atoms in a compound.
2. C – CH₄ is already the simplest ratio of 1 C : 4 H.
3. A – C₄H₈ simplified = CH₂ (dividing subscripts by 4).
4. A – C₆H₁₂O₆ → divide by 6 → CH₂O.
5. D – CH₄ (methane) cannot be simplified further.
6. B – The ratio C:H:O = 40:6.7:53.3 = approx 1:2:1 → CH₂O.
7. C – C₈H₁₈ → divide by 4 → C₂H₅.
8. B – H₂O₂ → divide by 2 = HO.
9. C – C₂H₂ is not the simplest form (CH is simpler).
10. A – C₆H₆ → divide by 6 = CH.
11. B – C₄H₁₀ → divide by 2 → C₂H₅.
12. E – CH is the most reduced ratio.
13. C – CH₂ is already the empirical form.
14. C – C:24g/12 = 2 mol, H:4g/1 = 4 mol → 2:4 = 1:2 → CH₂.
15. B – C:85.7/12 = 7.14, H:14.3/1 = 14.3 → 1:2 → CH₂.
16. B – Molecular mass is used for molecular formula, not empirical.
17. C – Empirical formulas give simplest atomic ratios.
18. C – C₆H₁₂O₆ can be simplified to CH₂O.
19. B – Iron and oxygen combine in a 2:3 ratio in Fe₂O₃.
20. A – C₂H₂ → divide by 2 → CH.
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