Free Carboxylic Acids MCQs with Answers

• A. they contain more hydrogen atoms
• B. the carboxylate ion formed is stabilised by delocalisation of the negative charge over two oxygen atoms
• C. they are liquids at room temperature
• D. their molecules are larger

Explanation: Losing the acidic hydrogen gives an ion whose charge is shared equally between the two oxygens, so the two carbon to oxygen bonds become…

• A. sodium ethanoate, water and carbon dioxide
• B. sodium ethanoate and hydrogen
• C. ethanol and carbon dioxide
• D. no reaction

Explanation: Being a stronger acid than carbonic acid, ethanoic acid displaces carbon dioxide from a carbonate, and the effervescence produced is the…

• A. donates electrons to the carboxyl group
• B. increases the molar mass
• C. withdraws electron density, spreading and stabilising the negative charge of the anion
• D. makes the molecule non polar

Explanation: The electron withdrawing inductive effect of chlorine pulls charge away from the carboxylate oxygens, so the ion is more stable and the…

• A. are ionised
• B. form dimers held together by two hydrogen bonds
• C. form covalent bonds with one another
• D. are non polar

Explanation: Two molecules pair up so that the hydroxyl hydrogen of each bonds to the carbonyl oxygen of the other, giving a cyclic dimer with double…

• A. ethanol under reflux with acidified potassium dichromate
• B. ethene with bromine water
• C. propanone with Tollens reagent
• D. ethane with oxygen at room temperature

Explanation: Refluxing keeps the intermediate ethanal in the flask so that oxidation continues to the acid, whereas distilling the product off as it…

• A. an amine
• B. an aldehyde
• C. an alcohol
• D. a carboxylic acid with the same number of carbon atoms as the nitrile

Explanation: The carbon of the nitrile group becomes the carbon of the carboxyl group, so hydrolysing ethanenitrile gives ethanoic acid and ammonia is…

• A. saponification
• B. esterification
• C. hydrolysis
• D. decarboxylation

Explanation: Esterification joins the two molecules with the elimination of water and is reversible, so the sulphuric acid serves both as catalyst and…

• A. the carboxylic acid and an alkene
• B. an aldehyde and water
• C. the sodium salt of the acid and an alcohol
• D. an amide and hydrogen

Explanation: Alkaline hydrolysis produces the carboxylate salt rather than the free acid, and because that salt cannot react back with the alcohol the…

• A. the amide
• B. the ester
• C. the carboxylate salt
• D. the acyl chloride

Explanation: Chlorine is a good leaving group and withdraws electron density strongly, so the carbonyl carbon of an acyl chloride is highly electron…

• A. ethyl ethanoate and hydrogen chloride
• B. ethanoic acid and chlorine
• C. ethane and water
• D. ethanal and hydrogen chloride

Explanation: The alcohol attacks the carbonyl carbon and chloride is expelled, giving the ester rapidly and irreversibly along with fumes of hydrogen…

• A. an aldehyde only
• B. a primary alcohol
• C. a ketone
• D. an alkane

Explanation: Lithium aluminium hydride is powerful enough to reduce the carboxyl group all the way to a primary alcohol, passing through the aldehyde…

• A. Ethanoic acid
• B. Propanoic acid
• C. Trichloroethanoic acid
• D. Butanoic acid

Explanation: Three electronegative chlorine atoms withdraw electron density powerfully and stabilise the carboxylate ion, so trichloroethanoic acid is…

• A. ethanol
• B. benzene
• C. starch
• D. natural fats and oils, which are esters of glycerol

Explanation: Boiling a fat with sodium hydroxide splits the three ester linkages and gives sodium salts of long chain fatty acids, the soap, together…

• A. CONH2, in which nitrogen is bonded directly to the carbonyl carbon
• B. COOH
• C. COOR
• D. COCl

Explanation: In an amide the nitrogen lone pair is delocalised into the carbonyl group, which is why amides are almost neutral rather than basic like…

• A. fails to react with alkalis
• B. acts as a reducing agent, giving a silver mirror with Tollens reagent
• C. contains no carboxyl group
• D. is insoluble in water

Explanation: Its carboxyl carbon also carries a hydrogen, so the molecule contains an aldehyde group as well and can be oxidised further to carbon…

• A. they ionise completely
• B. they are non polar
• C. the carboxyl group forms hydrogen bonds with water molecules
• D. they react with water chemically

Explanation: Both the carbonyl oxygen and the hydroxyl hydrogen can take part in hydrogen bonding with water, so the smaller acids dissolve freely, and…

• A. ethanoyl chloride, hydrogen chloride and phosphorus oxychloride
• B. chloroethane and water
• C. ethanol and chlorine
• D. ethanal only

Explanation: The hydroxyl group of the acid is replaced by chlorine, giving the far more reactive acyl chloride, and the misty fumes of hydrogen…

• A. Sodium hydroxide solution
• B. Sodium metal
• C. Sodium hydrogen carbonate solution
• D. Litmus paper alone

Explanation: Ethanoic acid gives brisk effervescence of carbon dioxide with hydrogen carbonate while phenol, being too weak an acid, gives no reaction…

• A. ethanoic acid
• B. butanoic acid
• C. propanoic acid
• D. propan-1-ol

Explanation: The molecule has three carbon atoms in total, and the carboxyl carbon is always counted as part of the chain and numbered one, so the name…

• A. ethanoic acid and ethanol
• B. ethanol and methanoic acid
• C. ethanoic acid and methanol
• D. ethanal and ethanol

Explanation: The first part of an ester name comes from the alcohol and the second from the acid, so ethyl ethanoate is made from ethanol and ethanoic…