Practice MDCAT Chemistry Easy MCQs with explanations — PMC, ETEA, NUMS entry test preparation.
Q1. In a chemical plant producing methanol from water gas, the reaction is carried out at 450C and 200 atm. Which catalyst is utilized?
Answer: ZnO and Cr2O3
Explanation: Methanol is industrially synthesized using ZnO-Cr2O3 catalyst at 450C. Al2O3 is a dehydrating agent, not used for methanol synthesis from water gas.
Q2. To prevent the illegal consumption of industrial-grade ethanol, 10% methanol is added to it. What is the common name for this specific mixture?
Answer: Methylated spirit
Explanation: Methylated spirit is ethanol with 10% methanol added to make it undrinkable. Rectified spirit is tempting but it contains 95.4% ethanol.
Q3. Phenol is often called carbolic acid. Which of the following reagents will react with phenol to demonstrate its acidic nature in a laboratory?
Answer: Sodium hydroxide
Explanation: Phenol is acidic enough to react with NaOH forming sodium phenoxide, but too weak to release CO2 from Na2CO3 or NaHCO3.
Q4. Formalin is used extensively in hospitals to preserve biological specimens. Which chemicals are the primary components of this solution, derived from methanol oxidation?
Answer: Formaldehyde and Water
Explanation: Formalin is a 40% aqueous solution of formaldehyde, produced by the catalytic oxidation of methanol. Ethanol oxidation produces acetaldehyde instead.
Q5. In an organic synthesis lab, a researcher needs to convert phenol into benzene. Which reagent should be used for this reduction process?
Answer: Zinc dust
Explanation: Phenol is reduced to benzene when its vapors are passed over heated zinc dust. Sodium metal would form sodium phenoxide instead.
Q6. During the final stage of industrial ethanol production from starch, glucose is converted into ethanol. Which enzyme is responsible for this biochemical transformation?
Answer: Zymase
Explanation: Zymase is the enzyme complex in yeast that converts simple sugars like glucose into ethanol and carbon dioxide during the final fermentation stage.
Q7. During the industrial fermentation of molasses, a specific enzyme is added to hydrolyze sucrose into glucose and fructose. Which enzyme is this?
Answer: Invertase
Explanation: Invertase hydrolyzes sucrose into glucose and fructose, whereas Zymase is the tempting wrong option that converts glucose into ethanol.
Q8. A student adds Lucas reagent to a test tube containing 2-methyl-2-propanol at room temperature. What is the most likely observation?
Answer: Oily layer forms immediately
Explanation: Tertiary alcohols like 2-methyl-2-propanol react instantly with Lucas reagent, while secondary alcohols take five to ten minutes to react.
Q9. In a laboratory quality control test, an unknown alcohol sample produces a yellow precipitate with iodine and sodium hydroxide. Which alcohol is it?
Answer: Ethanol
Explanation: Ethanol gives a positive iodoform test due to its structure, while methanol lacks the required methyl group attached to carbinol.
Q10. A dilute aqueous solution of phenol is treated with bromine water in a test tube. What visual change confirms the reaction?
Answer: White precipitate
Explanation: Phenol reacts with bromine water to form 2,4,6-tribromophenol, a white precipitate; 2-bromophenol is only formed in non-polar solvents.
Q11. In the fermentation of starch, maltose is converted to glucose, which is then converted to ethanol by which specific enzyme?
Answer: Zymase
Explanation: Zymase is the final enzyme in the fermentation pathway that converts glucose into ethanol and carbon dioxide.
Q12. Runge isolated a compound from coal tar in 1834 that is now commonly known as phenol. What was its original name?
Answer: Carbolic acid
Explanation: Phenol was historically called carbolic acid because it was first isolated from coal tar and exhibited acidic properties.
Q13. Lower molecular weight alcohols like methanol and ethanol show infinite solubility in water. What is the primary reason for this?
Answer: Hydrogen bonding
Explanation: Lower alcohols are soluble in water due to hydrogen bonding, which becomes less effective as the hydrophobic alkyl chain increases.
Q14. A lab technician needs to prepare Lucas reagent to differentiate between primary, secondary, and tertiary alcohols. What are the components?
Answer: Conc. HCl and ZnCl2
Explanation: Lucas reagent consists of equimolar amounts of concentrated hydrochloric acid and anhydrous zinc chloride.
Q15. The distillate obtained from the fermentation of starch or molasses is typically 'rectified spirit'. What is the percentage of ethanol in it?
Answer: 95% Ethanol
Explanation: Rectified spirit is a constant boiling mixture containing 95.4% ethanol and 4.6% water.
Q16. In a pharmaceutical preparation, 200g of rectified spirit is used as a solvent. According to PTB standards, what is the mass of water present?
Answer: 9.0 g
Explanation: Rectified spirit is 95.5% ethanol and 4.5% water. 9g is 4.5% of 200g; 10g would be exactly 5%, which is incorrect.
Q17. In the industrial synthesis of methyl alcohol from water gas, what specific pressure is maintained in the presence of ZnO-Cr2O3 catalyst?
Answer: 200 atm
Explanation: Methanol synthesis requires 200 atm pressure. 150 atm is the specific pressure used in Dow's process for phenol production.
Q18. To prevent the misuse of industrial alcohol, it is denatured. What is the percentage of methanol added to ethanol to form methylated spirit?
Answer: 10% Methanol
Explanation: Methylated spirit contains 10% methanol to make ethanol unfit for drinking. 5% is too low for the standard PTB definition.
Q19. Comparing physical properties, what is the standard boiling point of pure ethanol as mentioned in the PTB textbook?
Answer: 78.5 °C
Explanation: Ethanol (78.5 C) has a higher boiling point than Methanol (64.7 C) due to greater van der Waals forces. 100 C is water.
Q20. Which group of alcohols is described as being completely miscible in water in all proportions?
Answer: Methanol, Ethanol, Propanol
Explanation: Lower alcohols (C1-C3) are completely miscible in water due to hydrogen bonding. Butanol starts showing limited solubility.
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