Question 1

Which of the following functional groups will give a positive result in the Jones (chromic acid) oxidation test, indicated by the complete disappearance of the orange color and formation of a green precipitate within 5 seconds?

Accepted Answer

Primary alcohol

Question 2

A student performs the 2,4-dinitrophenylhydrazine (2,4-DNP) test on an unknown compound and observes the formation of a yellow precipitate within 10 seconds. Which functional group is most likely present in the unknown?

Accepted Answer

Aldehyde

Question 3

Which sequence of solubility and classification tests would best distinguish between a phenol and a carboxylic acid in a water-insoluble unknown?

Accepted Answer

Test solubility in 5% NaOH, then 5% NaHCO$$_3$$; phenol dissolves in NaOH but not NaHCO$$_3$$, carboxylic acid dissolves in both.

Question 4

A water-soluble unknown turns blue litmus paper red. Which functional group is most likely present?

Accepted Answer

Carboxylic acid

Question 5

Which of the following statements about the Lucas test is CORRECT?

Accepted Answer

Primary alcohols require 1 hour or more to show cloudiness, while tertiary alcohols react instantly.

Question 6

A student adds an unknown to 5% NaHCO$$_3$$ and observes vigorous bubbling and dissolution. What is the most likely functional group present?

Accepted Answer

Carboxylic acid

Question 7

Which test would best confirm the presence of a 2-alkanol (R-CH(OH)-CH$$_3) $$functional group in an unknown compound?

Accepted Answer

Iodoform test, positive result indicated by a bright yellow precipitate

Question 8

A student performs the cerium(IV) nitrate test on an unknown and observes a color change from yellow to orange-red. Which functional group is most likely present?

Accepted Answer

Alcohol

Question 9

Which of the following functional groups will NOT give a positive result in the 2,4-DNP test?

Accepted Answer

Ester

Question 10

A student adds an unknown to 5% NaOH and observes dissolution, but the compound is insoluble in 5% NaHCO$$_3. $$Which functional group is most likely present?

Accepted Answer

Phenol

Question 11

Which test would best distinguish between a primary and a tertiary alcohol?

Accepted Answer

Jones (chromic acid) oxidation test

Question 12

A student performs the iron(III) chloride test on an unknown and observes a deep purple color. Which functional group is most likely present?

Accepted Answer

Phenol

Question 13

Which of the following is a correct interpretation of a negative Jones (chromic acid) oxidation test?

Accepted Answer

The orange color persists and no green precipitate forms, indicating the compound is a tertiary alcohol or a ketone.

Question 14

A student adds an unknown to Lucas reagent and observes immediate cloudiness. Which functional group is most likely present?

Accepted Answer

Tertiary alcohol

Question 15

Which test would best confirm the presence of an ester functional group in an unknown compound?

Accepted Answer

Alkaline iron(III) hydroxamate test, positive result indicated by a red-blue or magenta color

Question 16

A student performs the iodoform test on an unknown and observes a bright yellow precipitate. Which functional group could be present?

Accepted Answer

2-alkanone (R-CO-CH$$_3)$$

Question 17

A student tests an unknown with litmus paper and observes that red litmus turns blue. Which functional group is most likely present?

Accepted Answer

Amine

Question 18

Which of the following statements about the 2,4-DNP test is TRUE?

Accepted Answer

A positive result is indicated by the formation of a yellow, orange, or red precipitate, confirming the presence of an aldehyde or ketone.

Question 19

A student adds an unknown to 5% NaOH and observes dissolution. Addition of concentrated HCl causes the compound to precipitate out of solution. Which functional group is most likely present?

Accepted Answer

Phenol

Question 20

Which of the following is a safety precaution that must be followed during qualitative organic analysis in the lab?

Accepted Answer

Wear proper PPE at all times and wash gloved hands frequently to avoid skin contact.

Qualitative Organic Analysis: Identification of Principal Functional Groups

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