701. What is formalin?
ⓐ. Pure liquid methanoic acid
ⓑ. Aqueous solution of methanal
ⓒ. Solid polymer of ethanoic acid
ⓓ. Alcoholic solution of propanone
Correct Answer: Aqueous solution of methanal
Explanation: Methanal is also called formaldehyde. Its aqueous solution is commonly known as formalin. Formalin is used as a disinfectant and preservative because methanal can harden proteins and prevent decay. It should not be confused with formic acid, which is methanoic acid, \(HCOOH\).
702. Which compound is commonly called formaldehyde?
ⓐ. \(CH_3CHO\)
ⓑ. \(CH_3COCH_3\)
ⓒ. \(HCOOH\)
ⓓ. \(HCHO\)
Correct Answer: \(HCHO\)
Explanation: Formaldehyde is the common name of methanal. Its formula is \(HCHO\), and it is the simplest aldehyde. It contains the aldehyde group with hydrogen attached on both sides of the carbonyl carbon. \(CH_3CHO\) is ethanal, \(CH_3COCH_3\) is propanone, and \(HCOOH\) is methanoic acid.
703. Which statement about methanal is correct?
ⓐ. Simplest aldehyde
ⓑ. It is the simplest ketone.
ⓒ. It is a methyl ketone.
ⓓ. It is an aromatic aldehyde.
Correct Answer: Simplest aldehyde
Explanation: Methanal, \(HCHO\), is the simplest member of the aldehyde family. It has only one carbon atom and contains the \(CHO\)-type aldehyde carbonyl arrangement. A ketone must have the carbonyl carbon bonded to two carbon groups, which methanal does not have. Aromatic aldehydes contain an aromatic ring, which is also absent in methanal.
704. Which use is commonly associated with formalin?
ⓐ. Fuel for soda-lime decarboxylation
ⓑ. Reagent for iodoform test
ⓒ. Preserving biological specimens
ⓓ. Catalyst for ester hydrolysis
Correct Answer: Preserving biological specimens
Explanation: Formalin is an aqueous solution of methanal. It is commonly used to preserve biological specimens because it prevents microbial decay and hardens tissues. This preserving action is related to the reactivity of methanal with proteins. It is not the reagent used for iodoform testing or ester hydrolysis.
705. Which carbonyl compound is widely used in making phenol-formaldehyde and urea-formaldehyde resins?
ⓐ. Ethanal
ⓑ. Methanal
ⓒ. Propanone
ⓓ. Benzaldehyde
Correct Answer: Methanal
Explanation: Methanal, also called formaldehyde, is used in the manufacture of important synthetic resins. Phenol-formaldehyde resins and urea-formaldehyde resins are formed by condensation reactions involving formaldehyde. Its high reactivity helps it link molecules together into polymeric networks. Ethanal and propanone are not the usual formaldehyde component in these named resins.
706. Which compound is commonly called acetaldehyde?
ⓐ. \(CH_3CHO\)
ⓑ. \(HCHO\)
ⓒ. \(CH_3COCH_3\)
ⓓ. \(CH_3COOH\)
Correct Answer: \(CH_3CHO\)
Explanation: Acetaldehyde is the common name of ethanal. Its formula is \(CH_3CHO\), and it contains the aldehyde group. Methanal, \(HCHO\), is formaldehyde. Propanone is acetone, while \(CH_3COOH\) is ethanoic acid.
707. Which statement best describes ethanal?
ⓐ. It is an acid that releases \(CO_2\) with \(NaHCO_3\).
ⓑ. It is a ketone that gives only iodoform test.
ⓒ. It is an aromatic aldehyde that fails Tollens’ test.
ⓓ. It is aliphatic aldehyde and gives Tollens’ test.
Correct Answer: It is aliphatic aldehyde and gives Tollens’ test.
Explanation: Ethanal, \(CH_3CHO\), is an aliphatic aldehyde. Aldehydes generally reduce Tollens’ reagent, producing a silver mirror. Ethanal also gives other aldehyde reactions such as \(2,4\)-DNP test and Fehling’s test. It is not a carboxylic acid, so it does not release \(CO_2\) with \(NaHCO_3\).
708. Ethanal is an important intermediate in the preparation of which acid by oxidation?
ⓐ. Methanoic acid
ⓑ. Propanoic acid
ⓒ. Ethanoic acid
ⓓ. Benzoic acid
Correct Answer: Ethanoic acid
Explanation: Ethanal contains the aldehyde group \(CHO\). Aldehydes are readily oxidised to carboxylic acids. Oxidation of \(CH_3CHO\) converts the \(CHO\) group into \(COOH\), giving \(CH_3COOH\). Therefore ethanal is converted into ethanoic acid on oxidation.
709. Which compound is commonly called acetone?
ⓐ. \(CH_3COCH_3\)
ⓑ. \(CH_3CHO\)
ⓒ. \(CH_3COCH_2CH_3\)
ⓓ. \(C_6H_5CHO\)
Correct Answer: \(CH_3COCH_3\)
Explanation: Acetone is the common name of propanone. Its formula is \(CH_3COCH_3\), and it is the simplest ketone. The carbonyl carbon is bonded to two methyl groups. \(CH_3CHO\) is ethanal, \(CH_3COOH\) is ethanoic acid, and \(C_6H_5CHO\) is benzaldehyde.
710. Which property makes acetone useful as a common laboratory solvent?
ⓐ. It is a strong mineral acid.
ⓑ. It is insoluble in water.
ⓒ. It releases \(CO_2\) with \(NaHCO_3\).
ⓓ. It dissolves organics.
Correct Answer: It dissolves organics.
Explanation: Acetone, \(CH_3COCH_3\), is a common organic solvent. It dissolves many organic compounds and is also miscible with water. Its usefulness comes from its polar carbonyl group and small molecular size. It is not a mineral acid and does not give bicarbonate effervescence.
711. Which test is expected to be positive for acetone because it is a methyl ketone?
ⓐ. Tollens’ test
ⓑ. Iodoform test
ⓒ. Sodium bicarbonate test
ⓓ. Fehling’s test
Correct Answer: Iodoform test
Explanation: Acetone has the structure \(CH_3COCH_3\), so it contains the methyl ketone group \(CH_3CO-\). Methyl ketones give the iodoform test with \(I_2/NaOH\). A yellow precipitate of iodoform, \(CHI_3\), is formed. Acetone usually does not give Tollens’ or Fehling’s tests because it is a simple ketone.
712. Which compound is commonly used as a solvent in nail polish remover?
ⓐ. Methanal
ⓑ. Ethanoic acid
ⓒ. Propanone
ⓓ. Methanoic acid
Correct Answer: Propanone
Explanation: Propanone is commonly known as acetone. It is used as a solvent in nail polish remover because it dissolves many organic substances present in nail polish. It evaporates readily, which also helps in such applications. Methanal is formaldehyde, while ethanoic acid and methanoic acid are carboxylic acids.
713. Which compound is also known as formic acid?
ⓐ. \(HCOOH\)
ⓑ. \(CH_3COOH\)
ⓒ. \(CH_3CHO\)
ⓓ. \(HCHO\)
Correct Answer: \(HCOOH\)
Explanation: Formic acid is the common name of methanoic acid. Its formula is \(HCOOH\). It is the simplest carboxylic acid and has special reducing behaviour. \(CH_3COOH\) is acetic acid, \(CH_3CHO\) is acetaldehyde, and \(HCHO\) is formaldehyde.
714. Methanoic acid is naturally associated with which source?
ⓐ. Vinegar
ⓑ. Nail polish remover
ⓒ. Formalin
ⓓ. Ant stings
Correct Answer: Ant stings
Explanation: Methanoic acid is also called formic acid. The word formic is historically associated with ants, and formic acid occurs in ant stings and some plant stings. It is a carboxylic acid and can show reducing behaviour. Vinegar is associated mainly with ethanoic acid, not methanoic acid.
715. Which compound is commonly called acetic acid?
ⓐ. \(HCOOH\)
ⓑ. \(CH_3COOH\)
ⓒ. \(CH_3CHO\)
ⓓ. \(CH_3COCH_3\)
Correct Answer: \(CH_3COOH\)
Explanation: Acetic acid is the common name of ethanoic acid. Its formula is \(CH_3COOH\). It contains the carboxyl group and reacts with bases to form ethanoate salts. \(HCOOH\) is formic acid, \(CH_3CHO\) is acetaldehyde, and \(CH_3COCH_3\) is acetone.
716. Vinegar is mainly an aqueous solution of which compound?
ⓐ. Methanal
ⓑ. Methanoic acid
ⓒ. Ethanoic acid
ⓓ. Propanone
Correct Answer: Ethanoic acid
Explanation: Vinegar is mainly a dilute aqueous solution of ethanoic acid, \(CH_3COOH\). Ethanoic acid gives vinegar its sour taste and acidic character. It reacts with \(NaHCO_3\) to release \(CO_2\), as carboxylic acids do. Methanal and propanone are carbonyl compounds but are not the main acid in vinegar.
717. What is glacial acetic acid?
ⓐ. Nearly pure ethanoic acid
ⓑ. Dilute aqueous methanal
ⓒ. A salt of methanoic acid
ⓓ. A mixture of acetone and water
Correct Answer: Nearly pure ethanoic acid
Explanation: Glacial acetic acid refers to nearly pure, water-free ethanoic acid. It is called glacial because it can solidify into ice-like crystals near ordinary laboratory temperatures. It is much more concentrated than vinegar. Vinegar is dilute aqueous ethanoic acid, not glacial acetic acid.
718. Which pair is correctly matched?
ⓐ. Formalin — ethanoic acid solution
ⓑ. Acetone — propanone
ⓒ. Vinegar — methanal solution
ⓓ. Formic acid — ethanal
Correct Answer: Acetone — propanone
Explanation: Acetone is the common name of propanone, \(CH_3COCH_3\). Formalin is aqueous methanal, not ethanoic acid solution. Vinegar is dilute ethanoic acid, not methanal solution. Formic acid is methanoic acid, \(HCOOH\), not ethanal.
719. Which compound is best matched with its common use?
ⓐ. Ethanoic acid — silver mirror reagent
ⓑ. Acetone — soda-lime mixture
ⓒ. Methanal — iodoform precipitate
ⓓ. Formalin — preservation of specimens
Correct Answer: Formalin — preservation of specimens
Explanation: Formalin is aqueous methanal and is widely used for preserving biological specimens. Acetone is mainly a solvent, not soda lime. Ethanoic acid is the acid present in vinegar, not Tollens’ reagent. Iodoform precipitate is \(CHI_3\), not methanal.
720. Which set contains only common names correctly paired with formulas?
ⓐ. Formaldehyde — \(CH_3CHO\), acetone — \(CH_3COOH\)
ⓑ. Acetic acid — \(HCOOH\), formic acid — \(CH_3COOH\)
ⓒ. Formaldehyde — \(HCHO\), acetone — \(CH_3COCH_3\)
ⓓ. Acetaldehyde — \(HCHO\), formic acid — \(CH_3CHO\)
Correct Answer: Formaldehyde — \(HCHO\), acetone — \(CH_3COCH_3\)
Explanation: Formaldehyde is methanal, \(HCHO\). Acetone is propanone, \(CH_3COCH_3\). Acetic acid is ethanoic acid, \(CH_3COOH\), and formic acid is methanoic acid, \(HCOOH\). Acetaldehyde is ethanal, \(CH_3CHO\).
