CBSE Class 12 Chemistry Aldehydes Ketone and Carboxylic Acids Worksheet Set A

Question. Which aldehyde will give Cannizzaro’s reaction?
(a) CH₃ CH₂ CH₂ CHO
(b) CH₃ CH₂ CHCHO
(c) (CH₃)₃CCHO
(d) (CH₃)₂CH₂CH₂ CHO
Answer. C

Question. Carboxylic acids are more acidic than phenol and alcohol because of
(a) Formation of dimers
(b) Highly acidic hydrogen
(c) Resonance stabilization of their conjugate base
(d) Intermolecular hydrogen bonding
Answer. C

Question. Which of the following orders of relative strengths of acids is correct?
(a) ClCH₂ COOH > FCH₂ COOH > BrCH₂ COOH
(b) ClCH₂ COOH > BrCH₂ COOH > FCH₂ COOH
(c) BrCH₂ COOH > ClCH₂ COOH > FCH₂ COOH
(d) FCH₂ COOH > ClCH₂ COOH > BrCH₂ COOH
Answer. D

Question. When ethanal is heated with Fehling’s solution it gives a precipitate of
(a) CuO
(b) Cu
(c) Cu + Cu₂ O + CuO
(d) Cu₂ O
Answer. D

Question. Formic acid and acetic acid can be distinguished chemically by
(a) Reaction with HCl
(b) Iodoform test
(c) Reaction with NH₃
(d) Tollens’ test
Answer. D

Question. Which of the following conversions can be carried out by Clemmensen Reduction?
(a) Benzaldehyde into benzyl alcohol
(b) Cyclohexanone into cyclohexane
(c) Benzoyl chloride into benzaldehyde
(d) Benzophenone into diphenyl methane
Answer. B

Question. In Clemmensen Reduction carbonyl compound is treated with…………
(a) Zinc amalgam + HCI
(b) Sodium amalgam + HCI
(c) Zinc amalgam + nitric acid
(d) Sodium amalgam + HNO₃
Answer. A

Question. Cannizzaro's reaction is not given by………..
(a) C₆H₅CHO
(b) H CHO
(c) CCl₃-CHO
(d) CH₃-CHO
Answer. D

Question. Which of the following compound is most reactive towards nucleophilic addition reactions?
(a) C₆H₅CHO
(b) H CHO
(c) CH₃-CO- CH₃
(d) CH₃-CHO
Answer. B

Question. The correct order of increasing acidic strength is……………
(a) Phenol < Ethanol < Chloroacetic acid < Acetic acid
(b) Ethanol < Phenol < Chloroacetic acid < Acetic acid
(c) Ethanol < Phenol < Acetic acid < Chloroacetic acid
(d) Chloroacetic acid < Acetic acid < Phenol < Ethanol
Answer. C

Question. The correct order of decreasing acidic strength is………….
(a) Dichloro acetic acid< Trichloroacetic acid < Chloroacetic acid < Acetic acid
(b) Trichloro acetic acid< Dichloroacetic acid < Chloroacetic acid < Acetic acid
(c) Trichloro acetic acid > Dichloroacetic acid > Chloroacetic acid > Acetic acid
(d) Dichloro acetic acid< Trichloroacetic acid < Chloroacetic acid < Acetic acid
Answer. C

Question. Tollens reagent is
(a) Ammoniacal silver bromide
(b) Ammoniacal silver nitrate
(c) Ammoniacal silver iodide
(d) Ammoniacal cuprous oxide
Answer. B

Question. Arrange the following molecules in the increasing order of Pka values
(a) Dichloro acetic acid< Trichloroacetic acid < Chloroacetic acid < Acetic acid
(b) Trichloro acetic acid< Dichloroacetic acid < Chloroacetic acid < Acetic acid
(c) Trichloro acetic acid > Dichloroacetic acid > Chloroacetic acid > Acetic acid
(d) Dichloro acetic acid< Trichloroacetic acid < Chloroacetic acid < Acetic acid
Answer. B

Question. Stephen reduction is used to prepare aldehydes from
(a) Acid chloride
(b) Alkane nitriles
(c) Acid amides
(d) Grignard reagent
Answer. B

Question. Ozonolysis of 2,3-Dimethyl but-2-ene gives
(a) one molecule of acetone and one molecule of butanone
(b) two molecule of acetone
(c) two molecules of propanal
(d) one molecule of propanal and one molecule of propanone
Answer. B

Question. Arrange the following molecules in the increasing order BP
(a) propane< popanal <propanone < propanol < propanoic acid
(b) propane> popanal >propanone > propanol > propanoic acid
(c) propane< popanone <propanal < propanol < propanoic acid
(d) propane< popanal <propanone < propanoic acid < propanol
Answer. A

Question. Acetophenone and benzophenone can be distinguished by
(a) Iodoform test
(b) Tollens Test
(c) Fehling’s test
(d) Benedicts test
Answer. A

Question. Acetaldehyde and benzaldehyde can be distinguished by
(a) Iodoform test
(b) Tollens Test
(c) Fehling’s test
(d) neutral FeCl₃
(a) a only
(b) both a and b
(c) both a and c
(d) d only
Answer. C

Question. Benedict solution provides
(a) Cu⁺²
(b) Cu⁺
(c) Ca⁺²
(d) Ba⁺²
Answer. A

Question. Fehlings solution B is
(a) Copper sulphate solution
(b) alkaline sodium potassium tartarate
(c) Alkaline sodium citrate
(d) ammoniacal silver nitrate
Answer. B

Question. Carbonyl compounds can be converted to hydrocarbons by
(a) Clemensons reduction
(b) reduction using NaBH₄ or LiAlH₄
(c) Wolf Kishner reduction
(d) by both a and c
Answer. D

Question. Oxidation of acetone using HNO₃ will give
(a) two molecules of acetic acid
(b) one molecule of propionic acid
(c) CH₃COOH + H₂O + CO₂
(d) two molecules of formic acid
Answer. C

ASSERTION - REASON TYPE QUESTIONS

Read the assertion and reason carefully to mark the correct option out of the options given below:
a. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
b. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
c. If the Assertion is correct but Reason is incorrect.
d. If both the Assertion and Reason are incorrect.

Question. Assertion: Chloroacetic acid has a lower pKa value than Acetic acid.
Reason: The – I effect of Cl further stabilizes the carboxylate anion formed by the loss of the proton.
Answer. A

Question. Assertion: Lower aldehyde and ketones are soluble in water but the solubility decreases as molecular mass increases.
Reason: Aldehydes and ketones can be distinguished by Tollen’s reagent.
Answer. B

Question. Assertion: Aldehydes undergo aldol condensation only if it has α-hydrogen.
Reason: The 𝖺-hydrogen in aldehydes are acidic in nature because the anion formed by the loss of the 𝖺-hydrogen is resonance stabilized.
Answer. A

Question. Assertion: Acetophenone and benzophenone can be distinguished by the iodoform test.
Reason: Acetophenone and benzophenone both are carbonyl compounds.
Answer. B

Question. Assertion: Benzaldehyde is more reactive than ethanal towards nucleophilic attack.
Reason: The overall effect of –I and +R effect of phenyl group decrease the electron density on the carbon atom of > C = O group in benzaldehyde.
Answer. A

Question. Assertion: Ketones are less reactive than aldehydes.
Reason: Ketones do not have alpha hydrogens
Answer. C

Question. Assertion: Dry HCl is a must for the reaction of an aldehyde with alcohol to form hemiacetal.
Reason: HCl protonates the carbonyl oxygen increasing the electrophilicity of the carbonyl carbon.
Answer. A

Question. 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.
Answer. A

Question. Assertion : Lower aldehydes and ketones are soluble in water but the solubility decreases as the molecular masses increase
Reason: Distinction between aldehydes and ketones can be made by Tollens’ test.
Answer. B

Question. Assertion: CH₃CHO is more reactive than CH₃COCH₃ towards reaction with HCN.
Reason : CH₃CHO is more polar and has less stearic hindrance, therefore, more reactive with HCN than CH₃COCH₃.
Answer. A

Question. Assertion : Carboxylic acids do not give reactions of carbonyl group.
Reason: Due to resonance
Answer. A

Question. Assertion : There are two -NH2 groups in semicarbazide (H₂NNHCONH₂). any one NH₂ group can involved in the formation of semicarbazone.
Reason : Its due to steric hindrance and electronic effect
Answer. D

Question. Assertion : Chloro acetic acid has lower pKa value than acetic acid
Reason : The –I effect of Cl further stabilises the carboxylate anion formed by the loss of the proton
Answer. A

Question. Assertion : Benzaldehyde resists nucleophilic addition in comparison with ethanal
Reason: The phenyl group in benzaldehyde is too bulky and therefore prevents attack of Nucleophile
Answer. C

Question. Assertion : Aldehydes undergo aldol condensation only if it has alpha hydrogen
Reason : The alpha hydrogen in aldehydes are acidic in nature because the anion formed by the loss of the alpha hydrogen is resonance stabilised .
Answer. A

Question. Assertion : Reactivity of ketones is more than aldehyde..
Reason : The carbonyl carbon of ketones is less electrophilic as compared to aldehyde.
Answer. D

Question. Assertion : Cannizzaro reaction is a self oxidation and reduction reaction of aldehyde donot having alpha hydrogens
Reason : Benzaldehyde shows cannizzaro reaction and gives benzyl alcohol and sodium salt of benzoic acid
Answer. B

Very Short Answer

Question. Define Rosenmund reduction?
Answer. Acyl chloride is hydrogenated over catalyst, palladium on barium sulphate is called Rosenmund reductio

Question. What is the use of ketones?
Answer. Ketones are used in the blending of perfumes and flavouring agents.

Question. What is the other name for dimethyl ketone?
Answer. The other name for the dimethyl ketone is acetone.

Question.What is hemiacetals?
Answer. Aldehydes react with one equivalent of monohydric alcohol in the presence of dry hydrogen chloride to yield alkoxyalcohol intermediate.

Question. Define amides?
Answer. The amide is a group of chemical substances and amine is an organic compound that is a derivative of ammonia.

Short Answer

Question. What do you mean by aromatic aldehydes?
Answer. Aromatic aldehydes are organic chemical compounds that contain a carbon hydroxide radical or group, CHO, and are used as precursor chemicals in the pharmaceutical and plastics industries. The two most commonly used aromatic aldehydes and aromatic ketones are formaldehyde and acetone

Question. Define carboxylic acid?
Answer. A carboxylic acid is an organic compound that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R–COOH, with Rn referring to the alkyl group. Deprotonation of a carboxylic acid gives a carboxylate anion.

Question. What do you mean by carbonyl group?
Answer. A carbonyl group is a chemically organic functional group composed of a carbon atom double-bonded to an oxygen atom → [C=O] The simplest carbonyl groups are aldehydes and ketones usually attached to another carbon compound.

Question. What do you understand by Stephen reaction?
Answer. Alkyl nitriles on reduction with stannous chloride and hydrochloric acid in dry ether give corresponding imine hydrochlorides which on acid hydrolysis, give corresponding aldehydes; this reaction is known as Stephen's reaction

Question. What is the structure of the carbonyl group?
Answer. The carbon atom present in the carbonyl group has sp2 hybridization and it developsnthree sigma (σ) bonds. However, the fourth valence electron of the carbon atom remains in the p-orbital. Thus, it develops π-bond by overlapping with the oxygen from the porbital of the oxygen atom. Additionally, the oxygen atom also contains two non-bonded pairs of electrons.

SHORT ANSWER QUESTIONS 

Question. Aldehydes and Ketones have lower boiling points than corresponding alcohols. Why?
Answer. The boiling points of aldehydes and ketones are lower than that of corresponding alcohols due to absence of intermolecular H–bonding in aldehydes and ketones.

Question. Account for the following :
CH₃CHO is more reactive than CH₃COCH₃ towards reaction with HCN.
Answer. It is a nucleophilic addition reaction, in which CN – acts as a nucleophile. CH₃CHO undergoes nucleophilic addition reactions faster than CH₃COCH₃ as in CH₃COCH₃ there are two electron releasing methyl groups attached to the carbonyl carbon that hinders the approach of nucleophile to carbonyl carbon and reduce the electrophilicity of the carbonyl group while in CH₃CHO, there is only one methyl group attached to carbonyl carbon.

Question. Arrange the following in order of increasing reactivity towards nucleophilic addition reaction Ethanal, propanal, propanone, butanone .
Answer. Due to steric hindrance & +I effect, the reactivity towards nucleophilic addition reaction decreases. So order is butanone< propanone < propanal < ethanol.

Question. Account for the following
(i) Higher carboxylic acid are insoluble in water. Why?
(ii) Why p-nitro benzoic acid has higher Ka value than benzoic acid?
(iii) The boiling points of aldehydes and ketones are lower than that of the corresponding acids.
Answer.
(i) Due to increased hydrophobic part, H-bonding does not take place. So higher carboxylic acid are insoluble in water.
(ii) Higher the Ka value, stronger is the aci(d) Nitro group has –R as well as –I effect which makes the O-H more polar hence p-nitro benzoic acid is stronger aci(d) (The conjugate base gets stabilised through delocalisation of the negative charge by inductive and /or resonance effects). So it has higher Ka value
(iii) The boiling points of aldehydes and ketones are lower than that of the corresponding acids due to intermolecular hydrogen bonding in carboxylic acids

Question. Account for the following :
(i) Oxidation of toluene to C₆H₅CHO with CrO₃ is carried out in presence of acetic anhydride.
(ii) Melting point of an acid with even number is higher than those of its neighbours with odd number of carbon atoms.
(iii) Aromatic acids are solid while most of aliphatic acids are liquids.
Answer. (i) Oxidation of toluene to C₆H₅CHO with CrO₃ is carried out in presence of acetic anhydride. to prevent further oxidation of C₆H₅CHO to benzoic aci(d)
(ii) Acids with even number of carbon atoms fit into crystal lattice. Hence melting point of an acid with even number is higher than those of its neighbours with odd number of carbon atoms. (iii)Aromatic acids have higher molecular weight and strong Van der Waals force of attraction as compared to aliphatic acids so they are solids

Long Answer

Question. State the difference between aldehydes and ketones?
Answer. 
1. Aldehydes are more reactive than ketones. Aldehydes undergo oxidation forming carboxylic acids whereas ketones cannot be oxidised without breaking the carbon chain.
2. Aldehydes end with the suffix al whereas ketones end with the suffix one.
3. Aldehydes are usually found in volatile compounds such as fragrance compounds whereas ketones are commonly found in sugars and are referred to as ketoses in general. However, there are aldehyde sugars which are called aldoses.
4. Aldehydes have the form of R-CHO whereas ketones have the form of R-CO-R.
5. Aldehydes usually more reactive than ketone whereas ketones usually less reactive than aldehydes.

Question. Explain the preparation of aldehydes from hydrocarbons?
Answer. Aromatic aldehydes are prepared from aromatic hydrocarbons by the following methods:
1. By oxidation of methylbenzene: Strong oxidising agents oxidised toluene and its derivatives to benzoic acids. It is possible to stop the oxidation at the aldehyde stage with the suitable reagents that convert the methyl group to an intermediate i.e. difficult to oxidise further. The following methods are used for this purpose are:
a. Use of the chromyl chloride oxidises methyl group to a chromium complex which on hydrolysis gives corresponding benzaldehyde, this reaction is called Etard reaction.
b. Use of chromic oxide, toluene or substituted toluene is converter to benzylidene diacetate on treating with the chromic oxide in acetic anhydride.
The benzylidene diacetate can be hydrolysed to corresponding benzaldehyde with aqueous acid.
2. By side chain chlorination followed by hydrolysis: side chain chlorination of toluene gives benzal chloride which on hydrolysis gives benzaldehyde, this is a commercial method of manufacture of benzaldehyde.
3. By Gatterman-Koch reaction: when benzene or its derivate is treated with carbon monoxide and hydrogen chloride in the presence of the anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde.

Question. What are the physical and chemical properties of the aldehydes and ketones?
Answer. Physical properties of aldehydes and ketone are:
1. Boiling point: The boiling point of aldehydes and ketones is higher than that of non-polar compounds (hydrocarbons) but lower than those of corresponding alcohols and carboxylic acids as aldehydes and ketones do not form Hbonds with themselves.
2. Solubility: Both aldehydes and ketones contain carbonyl group, therefore they undergo same reactions like nucleophilic addition reactions, oxidation, reduction,  halogenation etc.
Chemical properties of aldehydes and ketone are:
1. Inductive effect: Alkyl groups are electron donating in nature (i.e., show +IEffect).
Hence, the presence of alkyl groups attached to the carbonyl group increases the electron density on the carbonyl carbon thereby decreases its reactivity towards nucleophilic addition reactions.
2. Steric hindrance: The more the number and the bigger the size of the alkyl group, the more difficult for a nucleophile to attack due to steric hindrance (crowding).
3. Oxidation reaction: Aldehydes can be easily oxidised to carboxylic acids due to the presence of a hydrogen atom on carbonyl group which can be easily converted to OH group. Since ketones do not have any hydrogen atom attached to the carbonyl group, they cannot be oxidised easily, and therefore, strong oxidising agents are required for this purpose.

Question. State the difference between electrophilic and nucleophilic?
Answer. 
1. An electrophile is an atom or molecule that can accept an electron pair from an electron rich species and form a covalent bond whereas a nucleophile is an atom or molecule which can donate electron pairs.
2. Electrophiles undergo electrophilic addition and electrophilic substitution reactions whereas Nucleophiles undergo nucleophilic addition and nucleophilic substitution reactions.
3. Electrophiles are either positively charged or neutrally charged whereas Nucleophiles are either negatively charged or neutrally charged.
4. Electrophiles are also called Lewis acids whereas Nucleophiles are also called Lewis bases.
5. Electrophiles donate protons and accept protons whereas nucleophiles accept protons and donate electrons.

Question. Explain the preparation of ketones?
Answer. Ketones are prepared from ozonolysis of alkenes that are not monosubstituted (i.e., alkenes that have two alkyl groups attached to the same carbon of an alkene). Ozonolysis is a process in which ozone (O₃) is used to cleave a double bond and create two smaller carbonyl molecules. First, ozone is added to the double bond to form an ozonide. Then hydrolysis of the ozonide occurs, cleaving the molecule to form the two smaller molecules. Oxymercuration-demercuration hydration of terminal alkynes is used to prepare ketones. Oxymercuration is the reaction of an alkene with mercury (II) acetate in aqueous THF to form a three-membered mercurinium ion. Mercurinium is a positively charged mercury ion. Demercuration is the second step in the hydration of alkenes, where the acetoxymercury group is reduced with sodium borohydride to a hydrogen atom. Alkynes are hydrated to form enols that are immediately tautomerized to form ketones. Tautomers are compounds that differ only in the placement of a single proton. An acid, such as sulphuric acid, and a mercury salt are used as reagents. Protonation of the alkyne with an acid creates a stable carbocation intermediate. A carbocation is a carbon with a positive charge. The reaction occurs through a planar carbocation and is therefore not stereo selective. Water is the nucleophile that attacks the electrophilic carbocation. 

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