Carboxylic Acid MCQs with Answers
Which of the following functional groups defines a carboxylic acid?
Explanation:The functional group for carboxylic acids is the carboxyl group, which is written as -COOH.
The carboxyl group is a combination of which two groups?
Carbonyl and ether
Hydroxyl and aldehyde
Carbonyl and alkyl
Carbonyl and hydroxyl
Explanation:The carboxyl group is made up of a carbonyl group (>C=O) and a hydroxyl group (-OH).
What is the IUPAC name for formic acid?
Ethanoic acid
Propanoic acid
Butanoic acid
Methanoic acid
Explanation:Formic acid is also known as Methanoic acid in IUPAC nomenclature.
Acetic acid was first isolated from which source?
Ants
Butter
Fats and oils
Vinegar
Explanation:Acetic acid was first isolated from vinegar.
What is the common name for CH₃CH₂CH₂COOH?
Acetic acid
Propionic acid
Valeric acid
Butyric acid
Explanation:CH₃CH₂CH₂COOH is commonly known as Butyric acid.
Which of the following is an example of an aliphatic dicarboxylic acid?
Benzoic acid
Acetic acid
Formic acid
Oxalic acid
Explanation:Oxalic acid (Ethanedioic acid) is an example of an aliphatic dicarboxylic acid.
How many carboxyl groups are present in a tricarboxylic acid?
Explanation:Carboxylic acids are classified based on the number of carboxyl groups; 'tri' indicates three.
The IUPAC names of saturated monocarboxylic acids are derived from alkanes by changing the ending 'e' to:
Explanation:The IUPAC names of saturated monocarboxylic acids are alkanoic acids, ending with -oic acid.
Which of the following is the general formula for an aliphatic carboxylic acid?
Ar-C-OH
R-CHO
R-OH
R-C-OH (where R = H or an alkyl group)
Explanation:The general formula is R-COOH or R-C(=O)OH, where R is H or an alkyl group.
What type of carboxylic acid is benzoic acid?
Aliphatic monocarboxylic acid
Aliphatic dicarboxylic acid
Aromatic dicarboxylic acid
Aromatic monocarboxylic acid
Explanation:Benzoic acid is an aromatic monocarboxylic acid due to the benzene ring.
Primary alcohols and aldehydes can be oxidized to carboxylic acids using which of the following reagents?
LiAlH₄ in an acidic medium
NaBH₄ in an acidic medium
H₂/Ni in an acidic medium
K₂Cr₂O₇ in an acidic medium
Explanation:Potassium dichromate in acidic medium is a strong oxidizing agent for this purpose.
The hydrolysis of alkanenitriles to carboxylic acids requires boiling with:
Strong bases only
Water only
Organic solvents
Mineral acids or alkalis
Explanation:Boiling with mineral acids or alkalis hydrolyzes nitriles to carboxylic acids.
How many carbon atoms does the carboxylic acid produced from an alkyl halide via alkanenitrile hydrolysis have, compared to the original alkyl halide?
One less carbon atom
The same number of carbon atoms
Two carbon atoms more
One carbon atom more
Explanation:Cyanide adds one carbon atom during the reaction, increasing the chain length.
Carboxylic acids can be prepared from Grignard reagents by reacting them with:
Water
Alcohols
Aldehydes
Carbon dioxide
Explanation:Grignard reagents react with CO₂ followed by acidification to form carboxylic acids.
In the preparation of carboxylic acids from Grignard reagents, the addition product is reacted with:
An alkali
An organic base
An alcohol
A mineral acid
Explanation:The addition product is acidified with a mineral acid to yield the acid.
The hydrolysis of esters to form carboxylic acids is typically done by boiling with:
Dilute HCl
Aqueous ethanol
Acetic acid
Conc. sodium hydroxide
Explanation:This forms a salt which on acidification gives carboxylic acid.
Symmetrical alkenes when heated with alkaline KMnO₄ are cleaved at the double bond to form:
Alcohols
Ketones
Ethers
Carboxylic acids
Explanation:Alkaline KMnO₄ cleaves double bonds oxidatively to yield carboxylic acids.
What is the smell characteristic of the first three aliphatic acids (formic, acetic, propionic acid)?
Pleasant and fruity
Odorless
Sweet
Pungent
Explanation:They are colorless liquids with a characteristic pungent odor.
Why are the first four members of aliphatic acids very soluble in water?
Due to van der Waals forces
Due to ionic character
Due to their small size only
Due to hydrogen bonding
Explanation:Hydrogen bonding with water molecules makes them highly soluble.
Carboxylic acids have relatively high boiling points due to:
Strong dipole-dipole interactions
London dispersion forces
Covalent bonding
Intermolecular hydrogen bonding
Explanation:Hydrogen bonding between carboxylic acid molecules leads to higher boiling points.
In non-polar solvents like benzene, carboxylic acids exist as:
Monomers
Polymers
Open-chain trimers
Cyclic dimers
Explanation:In non-polar solvents, two acid molecules dimerize through hydrogen bonding.
What is the melting point trend observed for carboxylic acids with an even number of carbon atoms compared to their odd-numbered counterparts?
They have lower melting points.
Their melting points are similar.
There is no observable trend.
They have higher melting points.
Explanation:Even-numbered acids pack more efficiently in solids, leading to higher melting points.
Which of the following is a laboratory method for preparing acetic acid?
Oxidation of methane
Reduction of methyl cyanide
Fermentation of glucose directly
Oxidation of ethyl alcohol
Explanation:Ethyl alcohol is oxidized to acetic acid in laboratory synthesis.
The hydrolysis of ethanenitrile to acetic acid proceeds through which intermediate?
Ethyl acetate
Acetaldehyde
Acetic anhydride
Acetamide
Explanation:The intermediate formed is acetamide, which hydrolyzes to acetic acid.
What is 'glacial acetic acid' characterized by?
Its very low boiling point.
Its strong pungent smell.
Its immiscibility with water.
Its ability to freeze into an ice-like solid at 17 °C.
Explanation:Pure acetic acid solidifies at 17 °C, resembling ice — hence the term 'glacial'.
Which of the following statements about the carboxyl group's reactivity is true?
It only displays the chemistry of the carbonyl group.
It only displays the chemistry of the hydroxyl group.
It has no specific reactivity due to its stable nature.
It displays the chemistry of both the carbonyl and the hydroxyl groups.
Explanation:The carboxyl group displays the chemistry of both the carbonyl and the hydroxyl groups.
In most reactions of carboxylic acids, which part of the molecule is typically retained?
The hydroxyl group
The carbonyl group
The alkyl group
The carboxyl group
Explanation:In most reactions of carboxylic acids, the carboxyl group is retained.
The reactivity of carboxylic acid molecules is primarily a consequence of the presence of which group?
Hydroxyl group
Alkyl group
Carboxyl group as a whole
Carbonyl group
Explanation:The reactivity of these molecules is a consequence of the presence of the carbonyl group.
Carboxylic acids are considered weaker acids compared to:
Phenols
Alcohols
Water
Mineral acids
Explanation:Carboxylic acids are weaker acids than mineral acids.
When dissolved in water, carboxylic acids furnish which ion?
Explanation:They furnish H⁺ when dissolved in water.
What is formed when carboxylic acids react with bases like NaOH or KOH?
Esters
Ethers
Aldehydes
Salts
Explanation:Carboxylic acids react with bases (NaOH, KOH) to form salts.
Which gas is evolved when carboxylic acids decompose carbonates and bicarbonates?
Hydrogen gas
Oxygen gas
Methane gas
Carbon dioxide gas
Explanation:Carboxylic acids decompose carbonates and bicarbonates evolving carbon dioxide gas with effervescence.
The reaction of acetic acid with sodium carbonate produces sodium acetate, water, and:
Methane
Carbon monoxide
Hydrogen
Carbon dioxide
Explanation:2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O
When carboxylic acids react with active metals (Na, K, Ca, Mg), what is evolved along with the formation of their salts?
Oxygen gas
Nitrogen gas
Carbon dioxide gas
Hydrogen gas
Explanation:Carboxylic acids react with active metals (Na, K, Ca, Mg etc.) to form their salts with the evolution of hydrogen gas.
The -OH group of carboxylic acids can be replaced by which of the following to form acid derivatives?
H and CH₃
O and N
Only halogen atoms
X, OR and NH₂
Explanation:The -OH group can thus be replaced by X, OR and NH₂ to form halides, esters and amides, respectively.
What type of reaction occurs when a nucleophile attacks the carboxyl group, followed by the displacement of the -OH group?
Addition reaction
Elimination reaction
Oxidation reaction
Nucleophilic addition followed by substitution
Explanation:The addition of a nucleophile to the carboxyl group is always followed by the displacement of the -OH group by some other group, producing a carboxylic acid derivative.
The reaction of CH₃COOH with PCl₅ produces CH₃COCl, POCl₃, and:
Explanation:CH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl
Heating carboxylic acids with alcohols in the presence of concentrated H₂SO₄ leads to the formation of:
Ethers
Aldehydes
Ketones
Esters
Explanation:When carboxylic acids are heated with alcohols in the presence of concentrated H₂SO₄, esters are formed.
What is the characteristic smell of esters, often leading to their use as artificial flavors?
Pungent
Unpleasant
Sour
Fruity
Explanation:Esters have a fruity smell and are used as artificial flavors.
What are ammonium salts formed when carboxylic acids react with ammonia?
Esters
Acid anhydrides
Carboxylic acids
Acid amides
Explanation:Carboxylic acids react with ammonia to form ammonium salts which on heating produce acid amides.
Which reagent is used to dehydrate carboxylic acids on strong heating to form acid anhydrides?
Concentrated H₂SO₄
Lithium aluminum hydride (LiAlH₄)
Potassium permanganate (KMnO₄)
Phosphorus pentoxide (P₂O₅)
Explanation:Carboxylic acids are dehydrated on heating strongly in the presence of phosphorus pentoxide.
What is the product of the partial reduction of carboxylic acids with lithium aluminum hydride (LiAlH₄)?
Alkanes
Aldehydes
Ethers
Alcohols
Explanation:Carboxylic acids on reaction with lithium aluminum hydride (LiAlH₄) are reduced to alcohols.
What are carboxylic acids completely reduced to when reacted with HI and red phosphorus?
Alkenes
Alkynes
Aldehydes
Alkanes
Explanation:Carboxylic acids on reduction with HI and red phosphorus give alkanes.
Which of the following is true regarding the reactivity of carboxylic acids based on the carbonyl group?
The carbonyl group decreases the reactivity.
The carbonyl group has no influence on reactivity.
The carbonyl group only affects physical properties, not reactivity.
The reactivity is a consequence of the presence of the carbonyl group.
Explanation:The reactivity of these molecules is a consequence of the presence of the carbonyl group.
When CH₃COOH reacts with SOCl₂, what are the products?
CH₃COCl + H₂O
CH₃COCl + SO₃ + HCl
CH₃COOS + H₂O
CH₃COCl + SO₂ + HCl
Explanation:The reaction of CH₃COOH with SOCl₂ produces acetyl chloride (CH₃COCl), sulfur dioxide (SO₂), and hydrochloric acid (HCl).
What happens to the proton (H⁺) in the presence of water (H₂O) when a carboxylic acid dissociates?
It remains as H⁺
It forms a covalent bond with the carboxylate ion
It combines with the solvent to form an insoluble precipitate
It breaks away as H₃O⁺ ion
Explanation:In the presence of water (H₂O), the proton breaks away as H₃O⁺ ion.
What type of functional group is formed when the -OH group of a carboxylic acid is replaced by −NH₂?
Ester
Acyl halide
Anhydride
Amide
Explanation:The -OH group can be replaced by X, OR, and NH₂ to form halides, esters, and amides, respectively.
Which of the following is a key step in the mechanism of ester formation from carboxylic acids and alcohols?
Deprotonation of the carboxylic acid
Elimination of an alkane
Formation of a ketone intermediate
Protonation of the carboxylic acid
Explanation:The first step in the mechanism of ester formation (esterification) is the protonation of the carboxylic acid.
What is the product when ammonium acetate (CH₃COONH₄) is heated?
Acetic acid + Ammonia
Acetic anhydride + Water
Ethyl acetate + Water
Acetamide + Water
Explanation:Ammonium salts formed by the reaction of carboxylic acids with ammonia produce acid amides upon heating (CH₃COONH₄ → CH₃CONH₂ + H₂O).
The overall process by which carboxylic acids react with alcohols to form esters and water is known as:
Saponification
Hydrolysis
Dehydration
Esterification
Explanation:The formation of an ester when carboxylic acids are heated with alcohols in the presence of concentrated H₂SO₄ is known as esterification.
What happens to the -OH group of a carboxylic acid when it forms a derivative like an acyl halide, ester, or amide?
It is reduced to a hydrogen atom.
It is oxidized to a carbonyl group.
It remains unchanged.
It is replaced by another group.
Explanation:The addition of a nucleophile to the carboxyl group is always followed by the displacement of the -OH group by some other group, producing a carboxylic acid derivative.
Which of the following is NOT a common carboxylic acid derivative discussed in the text?
Acyl halides
Esters
Amides
Ethers
Explanation:The -OH group can be replaced by X, OR and NH₂ to form halides, esters and amides, respectively.
What is the product when acetic acid (CH₃COOH) reacts with PCl₅?
Acetic anhydride
Ethyl acetate
Acetamide
Acetyl chloride (CH₃COCl)
Explanation:The reaction of CH₃COOH with PCl₅ yields CH₃COCl (Acetyl chloride), POCl₃, and HCl.
Which reagent is used to convert carboxylic acids into acyl chlorides, along with SO₂ and HCl as by-products?
Explanation:Carboxylic acids react with SOCl₂ to form acyl chlorides, SO₂, and HCl.
The formation of an ester from a carboxylic acid and an alcohol in the presence of concentrated H₂SO₄ is known as:
Saponification
Hydrolysis
Amidation
Esterification
Explanation:When carboxylic acids are heated with alcohols in the presence of concentrated H₂SO₄, esters are formed.
Which of the following compounds has a fruity smell and is used as an artificial flavor?
Carboxylic acid
Aldehyde
Amide
Ester
Explanation:Esters have a fruity smell and are used as artificial flavours.
What is the product formed when carboxylic acids react with NH₃ and are subsequently heated?
Ammonium salt only
Acid anhydride
Alkyl nitrile
Acid amide
Explanation:Carboxylic acids react with ammonia to form ammonium salts which on heating produce acid amides.
The dehydration of carboxylic acids using phosphorus pentoxide (P₂O₅) on strong heating leads to the formation of:
Esters
Acid amides
Acyl halides
Acid anhydrides
Explanation:Carboxylic acids are dehydrated on heating strongly in the presence of phosphorus pentoxide to form acid anhydrides.
Which of the following is a common step in the mechanism of forming acyl chlorides from carboxylic acids using SOCl₂?
Addition of water
Reduction of the carbonyl group
Protonation of the alkyl group
Formation of a sulfinyl chloride intermediate
Explanation:The mechanism for the reaction of CH₃COOH with SOCl₂ shows the formation of an intermediate where sulfur is bonded to the carboxyl oxygen and a chlorine atom.
What is the product of the reaction between ethanoic acid (CH₃COOH) and ethanol (C₂H₅OH) in the presence of H₂SO₄?
Ethyl alcohol
Ethanoic anhydride
Acetamide
Ethyl acetate
Explanation:CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O.
The conversion of a carboxylic acid into an acyl halide involves the replacement of the -OH group by a:
Hydrogen atom
Alkoxy group
Amine group
Halogen atom
Explanation:The -OH group can be replaced by X (halogen) to form halides.
The reaction of CH₃COOH with NH₃ initially forms an ammonium salt (CH₃COONH₄). This is an example of a reaction involving:
The -OH group of the carboxylic acid
The complete carboxyl group
Oxidation of the acid
The hydrogen atom of the carboxyl group
Explanation:Carboxylic acids react with bases (like ammonia) to form salts by removing the hydrogen atom of the carboxyl group.
What is the name of the derivative formed when the -OH group of a carboxylic acid is replaced by an -OR group?
Amide
Acyl halide
Acid anhydride
Ester
Explanation:The -OH group can be replaced by OR to form esters.
Which reagent is used to convert acyl chlorides to carboxylic acids?
Explanation:Acyl halides are readily hydrolyzed by water to form their corresponding carboxylic acids.
What is the product when an acid anhydride reacts with an alcohol?
Acyl halide
Amide
Carboxylic acid only
Ester
Explanation:Acid anhydrides react with alcohols to form esters and a carboxylic acid.
How can an ester be converted back to its parent carboxylic acid?
By reduction with LiAlH₄
By heating with P₂O₅
By reaction with SOCl₂
By saponification
Explanation:Esters can be hydrolyzed back to carboxylic acids and alcohols. When done with strong bases, it's called saponification.
What is the product when an amide is hydrolyzed in the presence of an acid or a base?
An ester
An acyl halide
An acid anhydride
A carboxylic acid
Explanation:Amides undergo hydrolysis in the presence of acid or base to yield a carboxylic acid and an amine (or an ammonium salt).
Which of the following reactions is an example of an interconversion between carboxylic acid derivatives?
Carboxylic acid + Alcohol → Ester
Amide + Water → Carboxylic acid
Acyl halide + Water → Carboxylic acid
All of the above
Explanation:All options represent interconversion reactions of carboxylic acid derivatives.
The reaction of an acyl chloride with an alcohol yields:
An acid anhydride
An amide
A carboxylic acid
An ester
Explanation:Acyl chlorides are highly reactive and react with alcohols to form esters.
What product is formed when an acyl chloride reacts with ammonia?
An ester
An acid anhydride
A carboxylic acid
An amide
Explanation:Acyl chlorides react with ammonia to form amides.
Which derivative can be used to synthesize an amide from a carboxylic acid without going through the ammonium salt intermediate?
Ester
Acid anhydride
None of the above
Acyl halide
Explanation:Acyl halides react directly with ammonia or amines to form amides without needing an intermediate salt.
The reaction of an acid anhydride with an amine produces:
An ester and water
An acyl halide
An alcohol
A carboxylic acid
Explanation:Acid anhydrides react with amines to form amides and a carboxylic acid (or its salt).
Which of the following reagents is most suitable for the reduction of an ester to an alcohol?
Explanation:Esters can be reduced to alcohols using strong reducing agents like LiAlH₄.
What is the primary characteristic that makes acyl halides highly reactive among carboxylic acid derivatives?
The bulky halogen atom
The strong carbon-halogen bond
The presence of a hydrogen bond
The good leaving group ability of the halide ion
Explanation:Halide ions are excellent leaving groups, making acyl halides very reactive.
The conversion of an acid anhydride to a carboxylic acid can be achieved by:
Reaction with an alcohol
Reaction with an amine
Reduction with LiAlH₄
Reaction with water
Explanation:Acid anhydrides react with water (HYDROLYSIS) to form two molecules of carboxylic acid.
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