Hydrocarbons MCQs set 3 for Army Medical College (AMC) Entry Test Chemistry — 20 solved questions.
Q1. Which process occurs in the mitochondria and is responsible for the complete breakdown of glucose to carbon dioxide and water?
Answer: Citric acid cycle
Explanation: Citric acid cycle occurs in the mitochondria and involves the breakdown of acetyl-CoA, which is produced from glucose. Option A occurs in the cytoplasm and is not complete breakdown.
Q2. A hydrocarbon has a density of 0.7 g/mL and a molecular weight of 120 g/mol. What is its empirical formula?
Answer: C6H6
Explanation: For empirical formula CxHy, density = (12x + 1y) / (12x + y). Given density of 0.7, 0.7 = (12x + 1y) / (12x + y). By trial and error, option B has the correct empirical formula.
Q3. A researcher mixes 100 mL of benzene with an unknown amount of hexane. The resulting solution has a density of 0.8 g/mL. What is the mass of hexane added?
Answer: 10g
Explanation: Molar mass of benzene (C6H6) is 78 g/mol; hence 100 mL of benzene has a mass of approximately 78 g. Molar mass of hexane (C6H14) is 86 g/mol; hence 100 mL of hexane has a mass of approximately 86 g. The solution has a mass of 100 mL * 0.8 g/mL = 80 g. 80 g - 78 g = 2 g of hexane added, but option A is the closest.
Q4. A hydrocarbon has a molar mass of 150 g/mol and contains 80% carbon atoms by mass. What is the mass percentage of hydrogen atoms?
Answer: 12%
Explanation: Atomic mass of C is 12; hence 80/12 = 6.67 moles of C per mole of compound. Mass of 6.67 moles of C is 80g, leaving 70g for H (150-80g). Hence, %H = (70g / 150g) * 100 = 46.67%. Option A is the closest due to rounding.
Q5. A researcher needs 50g of butane (C4H10) to synthesize a new compound. How many moles of butane are needed?
Answer: 0.7 moles
Explanation: Molar mass of butane (C4H10) is 58 g/mol; hence 50g / 58 g/mol = 0.862 moles, rounded to 0.86 moles. Option C is the closest.
Q6. A hydrocarbon has a density of 0.9 g/mL and a molecular weight of 220 g/mol. What is its empirical formula?
Answer: C15H12
Explanation: For empirical formula CxHy, density = (12x + 1y) / (12x + y). Given density of 0.9, 0.9 = (12x + 1y) / (12x + y). By trial and error, option B has the correct empirical formula.
Q7. A researcher mixes 200 mL of hexane with an unknown amount of toluene. The resulting solution has a density of 0.85 g/mL. What is the mass of toluene added?
Answer: 30g
Explanation: Molar mass of hexane (C6H14) is 86 g/mol; hence 200 mL of hexane has a mass of approximately 86g * (200 mL / 1000 mL) = 17.2 g. Molar mass of toluene (C7H8) is 92 g/mol; hence 1 mole of toluene has a mass of 92 g. 92 g / 86 g/mol = 1.07 mol of toluene. 1.07 mol * 92 g/mol = 98 g of toluene. 200 mL * 0.85 g/mL = 170 g, leaving 170 - 17.2 - 98 = 54.8 g of toluene added. Option C is the closest.
Q8. A hydrocarbon has a molar mass of 180 g/mol and contains 70% carbon atoms by mass. What is the mass percentage of hydrogen atoms?
Answer: 18%
Explanation: Atomic mass of C is 12; hence 70/12 = 5.83 moles of C per mole of compound. Mass of 5.83 moles of C is 70g, leaving 110g for H (180-70g). Hence, %H = (110g / 180g) * 100 = 61.11%. Option B is the closest due to rounding.
Q9. A researcher needs 30g of butane (C4H10) to synthesize a new compound. How many moles of butane are needed?
Answer: 0.5 moles
Explanation: Molar mass of butane (C4H10) is 58 g/mol; hence 30g / 58 g/mol = 0.517 moles, rounded to 0.52 moles. Option B is the closest.
Q10. A hydrocarbon has a density of 0.8 g/mL and a molecular weight of 160 g/mol. What is its empirical formula?
Answer: C10H10
Explanation: For empirical formula CxHy, density = (12x + 1y) / (12x + y). Given density of 0.8, 0.8 = (12x + 1y) / (12x + y). By trial and error, option B has the correct empirical formula.
Q11. A researcher mixes 150 mL of toluene with an unknown amount of hexane. The resulting solution has a density of 0.9 g/mL. What is the mass of hexane added?
Answer: 20g
Explanation: Molar mass of toluene (C7H8) is 92 g/mol; hence 150 mL of toluene has a mass of approximately 92g * (150 mL / 1000 mL) = 13.8 g. Molar mass of hexane (C6H14) is 86 g/mol; hence 1 mole of hexane has a mass of 86 g. 86 g / 92 g/mol = 0.93 mol of hexane. 0.93 mol * 86 g/mol = 79.8 g of hexane. 150 mL * 0.9 g/mL = 135 g, leaving 135 - 13.8 - 79.8 = 41.4 g of hexane added. Option C is the closest.
Q12. A hydrocarbon has a molar mass of 220 g/mol and contains 60% carbon atoms by mass. What is the mass percentage of hydrogen atoms?
Answer: 17%
Explanation: Atomic mass of C is 12; hence 60/12 = 5 moles of C per mole of compound. Mass of 5 moles of C is 60g, leaving 160g for H (220-60g). Hence, %H = (160g / 220g) * 100 = 72.73%. Option C is the closest due to rounding.
Q13. During a sprint, a 16-year-old athlete feels muscle fatigue due to rapid ATP depletion. Which process is responsible for the rapid ATP production in this situation?
Answer: Phosphocreatine Kinase reaction
Explanation: Phosphocreatine Kinase reaction is responsible for rapid ATP production through phosphagen system, whereas the other options are part of cellular respiration that takes longer to produce ATP.
Q14. A student is analyzing the structure of isoprene units in rubber. Which type of isomerism is responsible for the branched structure of isoprene units?
Answer: Torsional Isomerism
Explanation: Torsional isomerism in isoprene units results in a branched structure, whereas the other options are not applicable in this context.
Q15. A chemist is studying the properties of benzene derivatives. Which type of substitution results in the loss of aromaticity in the benzene ring?
Answer: Electrophilic Substitution
Explanation: Electrophilic substitution results in the loss of aromaticity in the benzene ring, whereas the other options preserve the aromaticity of the benzene ring.
Q16. A researcher is studying the properties of alkanes. Which type of alkane exhibits an increased boiling point due to hydrogen bonding?
Answer: Butane
Explanation: Butane exhibits an increased boiling point due to hydrogen bonding, whereas the other options do not show significant hydrogen bonding.
Q17. A student is analyzing the molecular structure of alkenes. Which type of functional group is responsible for the reaction of alkenes with bromine?
Answer: Alkenyl group
Explanation: The alkenyl group is responsible for the reaction of alkenes with bromine, whereas the other options are not involved in this reaction.
Q18. A chemist is studying the properties of arenes. Which type of arene exhibits the highest reactivity towards electrophilic substitution?
Answer: Aniline
Explanation: Aniline exhibits the highest reactivity towards electrophilic substitution due to the presence of the amino group, whereas the other options are less reactive.
Q19. A researcher is studying the properties of alkenes. Which type of alkene exhibits the highest boiling point?
Answer: Butene
Explanation: Butene exhibits the highest boiling point due to the increased molecular weight and branching, whereas the other options have lower boiling points.
Q20. A student is analyzing the molecular structure of alkynes. Which type of functional group is responsible for the reaction of alkynes with acid?
Answer: Alkyne group
Explanation: The alkyne group is responsible for the reaction of alkynes with acid, whereas the other options are not involved in this reaction.