Organic Chemistry Practice Problems with Answers
Organic chemistry practice problems are essential tools for mastering reaction mechanisms, structure–property relationships, and quantitative reasoning in chemical transformations. These problems typically cover topics such as stoichiometry in organic reactions, reaction yields, molar relationships, kinetics, and stereochemistry. By solving numerical problems, students develop a deeper understanding of how organic reactions proceed and how to predict products and quantities formed under given conditions.
A well-designed set of practice problems helps reinforce fundamental concepts like mole calculations, limiting reagents, percentage yield, and concentration changes during reactions. In organic chemistry, numerical problems often involve multi-step synthesis, reagent calculations, and interpretation of reaction pathways. These exercises are especially useful for competitive exams and undergraduate coursework, as they integrate both conceptual understanding and mathematical application.
Additionally, practicing such problems improves analytical thinking and problem-solving speed. Many real-world applications, such as pharmaceutical synthesis and industrial chemical production, require precise quantitative calculations. Therefore, solving a wide variety of organic chemistry numerical problems prepares students for both academic success and practical chemical research or industry roles.
100 Organic Chemistry Numerical Problems with Answers
Section A: Mole & Stoichiometry
- How many moles are present in 46 g of ethanol (C₂H₅OH)?
Answer: 1 mol - Calculate mass of methanol in 2 moles.
Answer: 64 g - Moles in 78 g benzene (C₆H₆)?
Answer: 1 mol - Mass of 0.5 mol acetic acid?
Answer: 30 g - Number of molecules in 1 mol methane?
Answer: 6.022 × 10²³ - Moles in 28 g ethylene (C₂H₄)?
Answer: 1 mol - Mass of 3 mol propane?
Answer: 132 g - Moles in 44 g CO₂ (from combustion)?
Answer: 1 mol - Mass of 0.25 mol benzene?
Answer: 19.5 g - Moles in 15 g CH₄?
Answer: 0.94 mol
Section B: Limiting Reagent
- 2 mol ethene reacts with 1 mol H₂. Limiting reagent?
Answer: H₂ - 3 mol CH₄ + 4 mol O₂ → limiting?
Answer: O₂ - 1 mol benzene + 1 mol Br₂ → limiting?
Answer: Benzene - 2 mol ethanol + 1 mol O₂ → limiting?
Answer: O₂ - 5 mol H₂ + 2 mol Cl₂ → limiting?
Answer: Cl₂ - 1 mol acetylene + 3 mol H₂ → limiting?
Answer: Acetylene - 2 mol propane + 10 mol O₂ → limiting?
Answer: Propane - 4 mol CO + 2 mol O₂ → limiting?
Answer: O₂ - 1 mol C₂H₆ + 3 mol O₂ → limiting?
Answer: C₂H₆ - 2 mol ethanol + 2 mol Na → limiting?
Answer: Ethanol
Section C: Percentage Yield
- Theoretical yield = 100 g, actual = 80 g. % yield?
Answer: 80% - 50 g theoretical, 40 g actual. % yield?
Answer: 80% - 120 g theoretical, 90 g actual. % yield?
Answer: 75% - 200 g theoretical, 150 g actual. % yield?
Answer: 75% - 60 g theoretical, 30 g actual. % yield?
Answer: 50% - 80 g theoretical, 64 g actual. % yield?
Answer: 80% - 100 g theoretical, 70 g actual. % yield?
Answer: 70% - 90 g theoretical, 81 g actual. % yield?
Answer: 90% - 150 g theoretical, 120 g actual. % yield?
Answer: 80% - 110 g theoretical, 99 g actual. % yield?
Answer: 90%
Section D: Reaction Stoichiometry
- CH₄ + 2O₂ → CO₂ + 2H₂O
1 mol CH₄ produces?
Answer: 1 mol CO₂ - 2 mol CH₄ produces CO₂?
Answer: 2 mol - 1 mol ethanol combustion gives CO₂?
Answer: 2 mol - 3 mol ethanol → CO₂?
Answer: 6 mol - 1 mol benzene → CO₂?
Answer: 6 mol - 2 mol benzene → CO₂?
Answer: 12 mol - 1 mol propane → CO₂?
Answer: 3 mol - 2 mol propane → CO₂?
Answer: 6 mol - 1 mol ethene → CO₂?
Answer: 2 mol - 3 mol ethene → CO₂?
Answer: 6 mol
Section E: Concentration & Solutions
- Molarity of 1 mol in 1 L?
Answer: 1 M - 2 mol in 2 L?
Answer: 1 M - 0.5 mol in 1 L?
Answer: 0.5 M - 3 mol in 1 L?
Answer: 3 M - 1 mol in 0.5 L?
Answer: 2 M - 0.2 mol in 2 L?
Answer: 0.1 M - 5 mol in 5 L?
Answer: 1 M - 4 mol in 2 L?
Answer: 2 M - 0.1 mol in 1 L?
Answer: 0.1 M - 10 mol in 2 L?
Answer: 5 M
Section F: Empirical & Molecular Formula
- %C=40, %H=6.7, %O=53.3 → empirical formula?
Answer: CH₂O - Molar mass = 180 → molecular formula?
Answer: C₆H₁₂O₆ - %C=85.7, %H=14.3 → empirical?
Answer: CH₂ - Molar mass 28 → molecular?
Answer: C₂H₄ - %C=75, %H=25 → empirical?
Answer: CH₄ - %C=92.3, %H=7.7 → empirical?
Answer: CH - Molar mass 78 → molecular?
Answer: C₆H₆ - %C=60, %H=13.3, %O=26.7 → empirical?
Answer: C₂H₆O - Molar mass 46 → molecular?
Answer: C₂H₆O - %C=66.7, %H=11.1, %O=22.2 → empirical?
Answer: C₃H₆O
Section G: Reaction Kinetics (Basic)
- Rate doubles → order?
Answer: First order - Rate quadruples → order?
Answer: Second order - Half-life constant → order?
Answer: First order - Rate independent of concentration → order?
Answer: Zero order - Rate ∝ [A]² → order?
Answer: Second - Rate ∝ [A]³ → order?
Answer: Third - Half-life decreases with concentration → order?
Answer: Zero - Half-life inversely proportional → order?
Answer: Second - Rate constant unit s⁻¹ → order?
Answer: First - Rate constant unit mol⁻¹L s⁻¹ → order?
Answer: Second
Section H: Miscellaneous
- Degree of unsaturation for C₆H₆?
Answer: 4 - For C₂H₄?
Answer: 1 - For C₃H₈?
Answer: 0 - For C₄H₆?
Answer: 2 - For C₅H₁₂?
Answer: 0 - For C₆H₁₀?
Answer: 2 - For C₇H₈?
Answer: 4 - For C₈H₁₈?
Answer: 0 - For C₉H₁₀?
Answer: 5 - For C₁₀H₈?
Answer: 7
Section I: Gas Calculations
- 1 mol gas at STP volume?
Answer: 22.4 L - 2 mol gas → volume?
Answer: 44.8 L - 0.5 mol → volume?
Answer: 11.2 L - 3 mol → volume?
Answer: 67.2 L - 4 mol → volume?
Answer: 89.6 L - 5 mol → volume?
Answer: 112 L - 0.25 mol → volume?
Answer: 5.6 L - 6 mol → volume?
Answer: 134.4 L - 10 mol → volume?
Answer: 224 L - 0.1 mol → volume?
Answer: 2.24 L
Section J: Advanced Mixed Problems
- Combustion of 1 mol ethanol produces CO₂?
Answer: 2 mol - 2 mol ethanol needs O₂?
Answer: 6 mol - 1 mol acetylene combustion → CO₂?
Answer: 2 mol - 3 mol acetylene → CO₂?
Answer: 6 mol - 1 mol propane needs O₂?
Answer: 5 mol - 2 mol propane needs O₂?
Answer: 10 mol - 1 mol benzene needs O₂?
Answer: 7.5 mol - 2 mol benzene needs O₂?
Answer: 15 mol - 1 mol ethene needs O₂?
Answer: 3 mol - 2 mol ethene needs O₂?
Answer: 6 mol