Question 1

Which of the following functional groups can be distinguished using the 2,4-dinitrophenylhydrazine (DNPH) test?

Accepted Answer

Aldehydes and ketones

Question 2

A student performs the Tollen's test on an unknown compound and observes the formation of a silver mirror. Which functional group is most likely present in the compound?

Accepted Answer

Aldehyde

Question 3

During the dichromate test, a green solution is observed after adding the reagents to an unknown sample. What does this indicate about the sample?

Accepted Answer

The sample contains a primary or secondary alcohol

Question 4

Which of the following is the correct balanced equation for the oxidation of ethanol to acetaldehyde using potassium dichromate in acidic solution?

Accepted Answer

$$ \mathrm{C_2H_5OH} + \mathrm{K_2Cr_2O_7} + 4\mathrm{H_2SO_4} \rightarrow \mathrm{CH_3CHO} + \mathrm{Cr_2(SO_4)_3} + 2\mathrm{KHSO_4} + 7\mathrm{H_2O} $$

Question 5

Which observation indicates a positive result in the DNPH test for carbonyl compounds?

Accepted Answer

Formation of a red-orange precipitate

Question 6

A compound gives a positive result in the Lucas test within 5 minutes at room temperature. What is the most likely classification of this compound?

Accepted Answer

Secondary alcohol

Question 7

Which of the following statements best explains why tertiary alcohols do not give a positive result in the dichromate test?

Accepted Answer

Tertiary alcohols lack a hydrogen atom on the carbon bearing the hydroxyl group

Question 8

Which sequence of tests would best distinguish between methanol, acetone, and isopropanol?

Accepted Answer

Lucas test followed by DNPH test

Question 9

A student adds 2,4-dinitrophenylhydrazine to an unknown sample and observes no precipitate. What can be concluded about the sample?

Accepted Answer

The sample is likely an alcohol or ether

Question 10

Which of the following best describes the chemical principle behind the Tollen's test?

Accepted Answer

Reduction of silver ion to metallic silver by aldehydes

Question 11

In the Lucas test, what is the role of concentrated hydrochloric acid?

Accepted Answer

Provides chloride ions for substitution to form alkyl chlorides

Question 12

A student is given an unknown compound that gives a positive DNPH test and a negative Tollen's test. Which compound is most likely present?

Accepted Answer

Acetone

Question 13

Which of the following is a safety precaution that must be observed when performing the dichromate test?

Accepted Answer

Perform the test in a fume hood due to corrosive and oxidizing nature of the reagents

Question 14

Which of the following reactions is responsible for the formation of a silver mirror in the Tollen's test?

Accepted Answer

$$ \mathrm{RCHO} + 2\mathrm{[Ag(NH_3)_2]^+} + 3\mathrm{OH^-} \rightarrow \mathrm{RCOO^-} + 2\mathrm{Ag} + 4\mathrm{NH_3} + 2\mathrm{H_2O} $$

Question 15

Which of the following compounds would react fastest in the Lucas test?

Accepted Answer

tert-Butanol

Question 16

A student tests an unknown sample with dichromate and observes no color change. The sample also gives a negative DNPH test. Which functional group is most likely present?

Accepted Answer

Ether

Question 17

Which of the following best describes the purpose of using reference standards in the analysis of oxygen-bearing organic compounds?

Accepted Answer

To compare the reactions of known compounds with the unknown sample

Question 18

Which of the following is the correct order of increasing reactivity in the Lucas test?

Accepted Answer

Primary alcohol \u003c Secondary alcohol \u003c Tertiary alcohol

Question 19

A student is given an unknown compound that gives a positive dichromate test and a negative Lucas test. Which compound is most likely present?

Accepted Answer

Methanol

EXP. 8: Analysis of Oxygen-Bearing Organic Compounds

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