Question Set D

CBSE 12th Standard Chemistry Aldehydes , Ketones and Carboxylic Acids HOT Questions Study Material - QB365

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Questions:

Generic 2

3 x 2 = 6

Name the compound that will give,butanone on oxidation with alk.KMnO₄ solution.

Draw the molecular structure of the compound 4-methylpent-3-en-2-one.

What is Tollen's reagent? Write one usefulness of this reagent.

Generic 3

4 x 3 = 12

Give reasons for the following
(i) Carboxylic carbon is less electropilic than carbonyl carbon of aldehydes and ketones.
(ii) Propanal is more reactive than propanone towards addition of HCN.

Predict the products of the following reactions:
\(\text { (i) } \mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CH}_{3} \frac{(\text { a }) \mathrm{KMnO}_{4} / \mathrm{KOH}}{(\text { b }) \mathrm{H}^{+}} \text {? }\)

An organic compound with molecular formula C₉H₁₀O forms 2,4-DNP derivative, reduces Tollen's reagent and undergoes Cannizzaro's reaction.
On vigorous oxidation it gives 1,2-benzene dicarboxylic acid. Identify the compound.

Convert:
(i) Acetophenone to ethylbenzene
(ii) Ethanal to 2-aminoethanoic acid
(iii) Methyl chloride to ethanoic acid.

Multiple Choice Question

10 x 1 = 10

Of the following which is the product formed when cyclohexanone undergoes aldol condensation followed by heating?

(a)

(b)

(c)

(d)

Treatment of compound with NaOH solution yields

(a)

Phenol

(b)

Sodium phenoxide

(c)

Sodium benzoate

(d)

Benzophenone

10.

Select the reagent for the given conversion.
\(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{8} \mathrm{CH}_{2} \mathrm{OH} \longrightarrow \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{8} \mathrm{COOH}\)

(a)

KMnO₄ in acidic,neutral, alkaline media

(b)

K₂Cr₂O₇in acidic media

(c)

CrO₃ in acidic media

(d)

All of the above

11.

The distinguishing test between methanoic acid and ethanoic acid is

(a)

Tollens' test

(b)

sodium bicarbonate test

(c)

Litmus test

(d)

esterification test

12.

CH3COOH \(\xrightarrow {H_3O^{+}}\) B + H₂O In the above reaction, 'A' and 'B' respectively are

(a)

CH₃COOC₂H5, C₂H₅OH

(b)

CH₃CHO, C₂H₅OH

(c)

C2H5OH, CH3CHO

(d)

C₂H₅OH, CH₃COOC₂H₅

13.

The decreasin order of acidity amoung the following compounds, ethanol (1), 2, 2, 2-trifluorethanol (II), trifluoroacetic acid (III) and acetic acid (IV) is

(a)

III > II > IV > I

(b)

IV > III > II > I

(c)

I > II > III > IV

(d)

III > IV > II > I

14.

C₆H₅¹⁴COOH on heating with Na₂CO₃ realeases

(a)

CO₂

(b)

¹⁴CO₂

(c)

(d)

none of these

15.

The acid D obtained through the following sequence of reactions is: C₂H₅Br \(\xrightarrow{Alc.KOH}\) A \(\xrightarrow [ { CCI }_{ 4 } ]{ { Br }_{ 2 } } B\xrightarrow [ (excess) ]{ KCN } C\xrightarrow { { H }_{ 3 }{ O }^{ + } } D\)

(a)

succinic acid

(b)

malonic acid

(c)

maleic acid

(d)

oxalic acid

16.

In the Cannizaro reaction given below,
2 Ph^__CHO \(\xrightarrow{OH^{-}}\) Ph ^__ CH₂OH + PhCO^-_2, the slowest step is

(a)

the attack of - OH at the carbonyl group

(b)

the transfer of hydride ion to the carbonyl group

(c)

the transfer of hydride ion to the carbonyl group

(d)

the abstraction of a proton from the carboxylic acid

(e)

the deprotonation of Ph^__ CH₂OH

17.

Identify the correct order of boiling points of the following compounds :
CH₃CH₂CH₂CH₂OH (1), CH₃CH₂CH₂CHO (2), CH₃CH₂CH₂COOH (3)

(a)

1 > 2 > 3

(b)

3 > 1 > 2

(c)

1 > 3 > 2

(d)

3 > 2 > 1

Generic 5

2 x 5 = 10

18.

An organic compound (A) having molecular formula, C₂H₄O reduces Tollens' reagent. Two moles of (A) react with AI(OC₂H₅)₃ to yield C₄H₈O₂ (B) which reacts with NH₃ to give C₂H₆O (C) and C₂H₅NO (D). Identify A,B,C and D.

19.

Me₃CCH₂COOH is more acidic than Me₃SiCH₂COOH

Case Study Questions

2 x 4 = 8

20.

Read the passage given below and answer the following questions:
Aldehydes and ketones are reduced to primary and secondary alcohols respectively by NaBH₄ or LiAIH₄ as well as catalytic hydrogenation. The carbonyl group of aldehydes and ketones is reduced to group on treatment with Zn-Hg and cone, HCI (Clemmensen reduction) or with hydrazine followed by NaOH or KOH in highly boiling solvent such, as ethylene glycol (Wolff- Kishner reduction).
Aldehydes differ from ketones in their oxidation reactions. Aldehydes are easily oxidised to carboxylic acids on treatment with HNO₃, KMnO₄, K₂Cr₂O₇ etc. Even mild oxidising agents mainly Tollens' reagent and Fehling's solution also oxidise aldehydes. Ketones are generally oxidised under vigorous conditions i.e., strong oxidising agents and at elevated temperatures, to give mixture of carboxylic acids having lesser number of C-atoms than the parent ketone.
The following questions are multiple choice questions. Choose the most appropriate answer:
(i) Which of the following cannot be made by reduction of ketone or aldehyde with NaBH₄ in methanol?

(a) 1-Butanol	(b) 2-Butanol
(c) 2-Methyl-I-propanol	(d) 2-Methyl-2-propanol

(ii) The carbonyl compound producing an optically active product by reaction with LiAlH₄ is

(a) propanone

(b) butanone

(c) 3-pentanone

(d) benzophenone

(iii) A substance C₄H₁₀O(X) yields on oxidation a compound C₄H₈O which gives an oxime and a positive iodoform test. The substance X on treatment with cone. H2S04 gives C4Hs. The structure of the compound (X) is

(a) CH₃CH₂CH₂CH₂OH	(b) CH₃CH(OH)CH₂CH₃
(c) (CH₃)₃COH	(d) CH₃CH₂-O-CH₂CH₃

(iv) In the oxidation of by acidified K₂Cr₂O₇, the products are

21.

Read the passage given below and answer the following questions :
When an aldehyde with no a-hydrogen reacts with concentrated aqueous NaOH, half the aldehyde is converted to carboxylic acid salt and other half is converted to an alcohol. In other words, half of the reactant is oxidized
and other half is reduced. This reaction is known as Cannizzaro reaction

The following questions are multiple choice questions. Choose the most appropriate answer :
(i) A mixture of benzaldehyde and formaldehyde on heating with aqueous NaOH solution gives

(a) benzyl alcohol and sodium formate	(b) sodium benzoate and methyl alcohol
(c) sodium benzoate and sodium formate	(d) benzyl alcohol and methyl alcohol.

(ii) Which of the following compounds will undergo Cannizzaro reaction?

(a) CH₃CHO	(b) CH₃COCH₃
(c) C₆H₅CHO	(d) C₆H₅CH₂CHO

(iii) Trichloroacetaldehyde is subjected to Cannizzaro's reaction by using NaOH. The mixture of the products contains sodium trichloroacetate ion and another compound. The other compounds is

(a) 2, 2, 2-trichloroethanol	(b) trichloromethanol
(c) 2, 2, 2-trichloropropanol	(d) chloroform

(iv) Which of the following reaction will not result in the formation of carbon-carbon bonds?

(a) Cannizzaro reaction	(b) Wurtz reaction
(c) Reimer- Tiemann reaction	(d) Friedel-Crafts acylation

Assertion and reason

4 x 1 = 4

22.

Assertion: Even though there are two NH₂ groups in semicarbazide, only one reacts with carbonyl compounds
Reason: Semicarbazide has two NH₂ groups out of which one is in resonance with the carbonyl group.
Codes:
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.
(e) If the assertion and reason both are false

23.

Assertion: The \(\alpha\)-hydrogen atom in carbonyl compounds is less acidic.
Reason: The anion formed after the loss of \(\alpha\)-hydrogen atom is resonance stabilised.
Codes:
(a) Assertion and reason both are correct and reason is correct explanation of assertion.
(b) Assertion and reason both are wrong statements.
(c) Assertion is correct but reason is wrong statement.
(d) Assertion is wrong but reason is correct statement.
(e) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

24.

Assertion: Carboxylic acids have higher boiling points than alkanes.
Reason: Carboxylic acids a;e resonance hybrids.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

25.

Assertion: Hydrogen bonding in carboxylic acids is stronger than alcohols.
Reason: Highly branched carboxylic acids are more acidic than unbranched acids.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

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Answers Key:

Generic 2

3 x 2 = 6

Butan-2-ol.

It is ammoniacal silver nitrate (agNO₃ + NH₄OH) solution. It is used as mild oxidising agent to test the presence of aldehyde group.

Generic 3

4 x 3 = 12

(i) This is because the lone pairs on oxygen atom attached to hydrogen atom in the -COOH group are involved in resonance.
(ii) This is because of the presence of alkyl groups on both of the carbonyl carbon, propanone is strically more hindered than propanol, making it less reactive to nucleophilic attack.

\(\text { (i) } \mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CH}_{3} \frac{(\mathrm{a}) \mathrm{KMnO}_{4} / \mathrm{KOH}}{\text { (b) } \mathrm{H}^{+}} \mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{COOH}\)

(i) As the given compound with molecular formula C₉H₁₀O, forms a 2,4-DNP derivative and reduces Tollen's reagent, thus it must be an aldehyde.
(ii) As it undergoes Cannizzaro reaction, hence -CHO group is directly attached to the benzene ring.
(iii) On vigorous oxidation, it gives 1,2-benzenedicarboxylic acid. Therefore, it must be an ortho-substituted benzaldehyde and the only o-substituted aromatic aldehyde which have C₉H₁₀O molecular formula is o-ethyl benzaldehyde.
Reactions involved

Multiple Choice Question

10 x 1 = 10

(a)
Phenol

10.

(d)
All of the above

11.

(a)
Tollens' test

12.

(d)
C₂H₅OH, CH₃COOC₂H₅

13.

(d)
III > IV > II > I

14.

(a)
CO₂

15.

(a)
succinic acid

16.

(b)
the transfer of hydride ion to the carbonyl group

17.

(b)
3 > 1 > 2

Generic 5

2 x 5 = 10

18.

(i) Since compound (A) with M.F. C₂H₄O reduces Tollens' reagent, it must be an aldehyde, i.e., acetaldehyde (CH₃HO).
\(\underset{Acetaldehyde}{CH_3CHO}+\underset{Tollens\ reagent}{2[Ag(NH_3)_2]^+}+3OH^-\longrightarrow CH_3COO^-+2Ag\downarrow+4NH_3+2H_2O\)
(ii) In presence of Al(OC₂H₅)₃ aldehydes undergo Tischenko reaction to give esters. Thus, when two moles of acetaldehyde (CH₃CHO) react in presence of AI(OC₂H₅)₃ ethyl acetate (B) with M.F. C₄H₈O₂ is produced
\(\underset{Acetaldehyde(A)\\(Two\ moles)}{CH_3CHO+OHCCH_3}\xrightarrow[(Tischenko reaction)]{Al(OC_2H_5)_3}\underset{Ethyl\ acetate\\ M/F.\ C_4H_8O_2}{CH_3COOCH_2CH_3}\)
(iii) The structure of ethyl acetate (B) is confirmed by the observation that on treatment with NH₃, it gives one molecule of an alcohol, i.e., ethyl alcohol, CH₃CH₂OH (C) and one molecule of an amide, i.e., acetamide, CH₃CONH₂(D)
\(\underset{Ethyl\ acetate(B)}{CH_3COOCH_2CH_3}\xrightarrow{NH_3}\underset{Ethyl alcohol (C)\\ M.F. C_2H_6O}{CH_3CH_2OH}+\underset{Acetamide (D)\\ M.F. C_2H_5NO}{CH_3CONH_2}\)

19.

Si (E.N. = 8) is more electropositive than C (E.N. = 2.5), therefore, Me₃Si (trimethylsilyl group) has greater +l-effect than that of Me₃C (r-butyl group). As a result, Me₃Si intesifies the -ve charge on the carboxylate ion relative to r-butyl group and hence Me₃CCH₂COOH is a stronger acid that Me₃SiCH₂COOH.

Case Study Questions

2 x 4 = 8

20.

(i) (d): 2-Methyl-2-propanol is It cannot be obtained by reduction of an aldehyde or ketone with NaBH₄·

2-Butanone forms oxime on reaction with hydroxylamine (NH₂OH) and also gives positive iodoform test.

21.

(i) (a): It is an example of cross Cannizzaro reaction where aromatic aldehyde gets reduced to alcohol and aliphatic aldehyde gets oxidised to its sodium salt (both aldehydes must not contain any \(\alpha\)-hydrogen).

(ii) (c)
(iii) (a): The Cannizzaro product of given reaction yields 2, 2, 2-trichloroethanol.

(iv) (a): C-C bond is not formed in Cannizzaro reaction while other reactions result in the formation of C-C bond.

Assertion and reason

4 x 1 = 4

22.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

23.

(d) Assertion is wrong but reason is correct statement.

24.

(b): Boiling points of carboxylic acids are higher due to th.eir tendency to associate and form dimers to a greater extent by hydrogen bonding.

25.

(c): Highly branched carboxylic acids are less acidic than unbranched acids. The +I effect of alkyl groups in branched acid increases the magnitude of negative charge. Thus, -COOH group is shielded from solvent molecules and cannot be stabilized by solvation as effectively as in unbranched carboxylic acids.