Hsslive XII Chem 8: Aldehydes, Ketones & Carboxylic Acids Past Paper Questions & Answers PDF

Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® Previous HSE questions and Answers for the chapter “Aldehydes, Ketones and Carboxylic Acids” 1. Aliphatic aldehydes differ from aromatic aldehydes. a) Give one example each fo...

Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® Previous HSE questions and Answers for the chapter “Aldehydes, Ketones and Carboxylic Acids” 1. Aliphatic aldehydes differ from aromatic aldehydes. a) Give one example each for an aliphatic aldehyde and an aromatic aldehyde containing seven carbon atoms. b) Give one reaction in which the above aldehydes differ. (3) [March 2008] Ans: (a) Aliphatic aldehyde: CH3-(CH2)5-CHO (heptanal) Aromatic aldehyde: C6H5-CHO (Benzaldehyde) (b) When heated with Fehling’s solution A and B, heptanal gives a red precipitate, while Benzaldehyde does not. 2. Nucleophilic addition reaction is a characteristic of carbonyl group. a) Explain this with specific examples, how the reaction takes place, (2) b) i) Show the order of reactivity of following compounds in nucleophilic addition; CH3-CHO, CH3-CO-CH3, H-CHO (1) ii) Justify your answer. (2) [March 2009] Ans: (a) The nucleophile attacks the electrophilic sp2 hybridised carbon atom of the carbonyl group. As a result, the hybridisation of carbon changes from sp to sp3 and a tetrahedral alkoxide intermediate is 2 produced. This intermediate captures a proton from the reaction medium to give the product. E.g. Addition of HCN. (b) i) The decreasing order of reactivity towards nucleophilic addition reaction is H-CHO > CH3-CHO > CH3-CO-CH3. This order is due to the electron releasing effect of CH3 groups and steric hindrance. 3. a) Show how aldehyde reacts with the following reagents. i) NH2CONHNH2 (Semi carbazide) ii) Zinc amalgam and conc. HCl (2) b) i) How can you manufacture formic acid from CO? (1) ii) Suggest a chemical test to distinguish this acid from acetic acid. Account for the observation. (2) [March 2009] Ans: a) (i) Aldehydes react with semicarbazide to form semicarbazone. R-CHO + NH2-NH-CO-NH2 → R-CH=N-NH-CO-NH2 + H2O (semicarbazone) (ii) Aldehydes when treated with zinc amalgam and concentrated hydrochloric acid to form alkanes. CH3-CHO + [H] Zn/Hg CH3-CH3 b) i) Carbon monoxide reacts with aq. NaOH to form sodium formate, this on acidification with dil. H2SO4 to form formic acid. CO + NaOH H2O HCOONa H2SO4 HCOOH ii) Iodoform test. When acetic acid is treated with sodium hypoiodite (NaOI), we get an yellow ppt of iodoform. This reaction is not answered by formic acid. Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 1  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® 4. a) Aldehydes and ketones are organic compounds containing carbonyl group. i) Write a chemical reaction used to distinguish between aldehydes and ketones. (1) ii) Aldehydes and ketones can be subjected to Clemmensen reduction and Wolff-Kishner reduction. Name the reagents in both cases. (1) b) How will you make the following conversions: i) Ethanoic acid to ethanol. ii) Propanoic acid to 2-chloropropanoic acid iii) Toluene to benzoic acid. (3) [March 2010] Ans: (a) i) Tollen’s test or Fehling’s test ii) Clemmensen reduction: Zinc amalgam and Conc. HCl Wolff-Kishner reduction: Hydrazine & KOH in ethylene glycol. (b) i) By reduction using LiAlH4 followed by acidification, ethanoic acid gets converted to ethanol. CH3-COOH i) LiAlH4/ether or B2H6 ii) H3O+ CH3-CH2OH ii) When treated with chlorine in the presence of red phosphorus propanoic acid gets converted to 2- chloropropanoic acid. CH3-CH2-COOH i) Cl2/ Red P ii) H2O CH3-CHCl-COOH + HCl Propanoic acid 2-chloropropanoic acid iii) Toluene when heated with alkaline KMnO4 followed by acidification, we get benzoic acid. COOH 5. NO2 is an aromatic acid NO2 a) What is its IUPAC name? (½) b) Explain the conversion of the above acid to the following: CHO CH2OH CH2OH i) NO2 ii) NO2 iii) NH2 NO2 NO2 NH2 (4½) [March 2011] Ans: (a) 3,4-Dinitrobenzoic acid (b) i) 3,4 –dinitrobenzoic acid is treated with thionyl chloride (SOCl2) followed by treating with H2 in presence of Pd supported over BaSO4 (Rosenmund’s reduction) we get 3,4-dinitrobenzaldehyde. COOH COCl CHO SOCl2 H2/Pd NO2 NO2 NO2 NO2 NO2 NO2 NO2 ii) 3,4 –dinitrobenzoic acid is reduced with diborane or LiAlH4 followed by hydrolysis, we get 3,4- dinitrobenzyl alcohol. Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 2  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® COOH CH2OH i) B2H6 NO2 iiii) H2O NO2 NO2 NO2 NO2 iii) 3,4 –dinitrobenzoic acid is treated with LiAlH4 followed by reduction with H2 in presence of Pd (or, by Fe and HCl or Sn and HCl), we get 3,4-diaminobenzyl alcohol. COOH CH2 OH CH2OH LiAlH4 H2/Pd NO2 NO2 NO2 NH2 NO2 NO2 NH2 6. Aldehydes resemble ketones in many respects. a) Give the reason for their resemblance. (1) b) Give a reaction in which aldehydes resemble ketones. (1) c) Write two tests to distinguish between aldehydes and ketones. (2) d) What is Cannizzaro reaction? (1) [SAY 2011] Ans: a) Because of the presence of carbonyl group in both aldehyde and ketones. b) Both aldehydes and ketones undergo nucleophilic addition reaction with HCN and form cyanohydrins. c) Aldehydes form bright silver mirror when heated with Tollens’ reagent (Tollens’ test). When heated with Fehling’s solutions, aldehydes form red ppt of cuprous oxide (Fehling’s test). These two tests are not answered by ketones. d) Aldehydes having no α-hydrogen atom, when treated with conc. KOH undergo self oxidation and reduction (disproportionation) to form alcohol and carboxylic acid salt. This reaction is called Cannizzaro reaction. 𝐶𝑜𝑛𝑐. 𝐾𝑂𝐻 2 HCHO → CH3-OH + H-COOK Formaldehyde methanol potassium formate 7. a) Which name reaction is used to reduce CH3-CO-Cl to CH3-CHO? (1) b) Aldehydes and ketones undergo reactions due to the presence of α-hydrogen atom. i) Write the name reaction of aldehyde which takes place only because of the presence of α-hydrogen atom. (1) ii) How will you bring about the above reaction? (1) c) i) CH2Cl-COOH is a strong acid than CH3COOH. Why? ii) How will you convert CH3-COOH to CH2Cl-COOH? (2) [March 2012] Ans: (a) Rosenmund’s reduction b) i) Aldol condensation ii) By treating with dilute alkali (NaOH or KOH). c) i) Due to the electron withdrawing inductive effect (-I effect) of Chlorine atom. ii) By treating with Cl2 in presence of red phosphorus (HVZ reaction). 8. a) Complete the following: Write down the structures of A, B and C. 𝐾𝑀𝑛𝑂4 i) CH3-CH2-CHO → A 𝑍𝑛 𝑎𝑚𝑎𝑙𝑔𝑎𝑚/𝐶𝑜𝑛𝑐.𝐻𝐶𝑙 ii) CH3-CH2-CO-CH3 → B (𝑖) 𝐵𝑟𝑜𝑚𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (𝑖𝑖) 𝐻2 𝑂 iii) CH3-CH2-CH2-COOH → C Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 3  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® b) Write down the IUPAC names of A, B and C. (1½) c) Explain the following reactions: i) Cannizzaro reaction. ii) Esterification. (1) [SAY 2012] Ans: (a) 𝐾𝑀𝑛𝑂4 i) CH3-CH2-CHO → CH3-CH2-COOH 𝑍𝑛 𝑎𝑚𝑎𝑙𝑔𝑎𝑚/𝐶𝑜𝑛𝑐.𝐻𝐶𝑙 ii) CH3-CH2-CO-CH3 → CH3-CH2-CH2-CH3 (𝑖) 𝐵𝑟𝑜𝑚𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (𝑖𝑖) 𝐻2 𝑂 iii) CH3-CH2-CH2-COOH → CH3-CH2-CHBr-COOH (b) IUPAC name of A is propanoic acid, B is butane and C is 2-Bromobutanoic acid. (c) i) Cannizzaro reaction: Aldehydes having no α-hydrogen atom, when treated with conc. KOH undergo self-oxidation and reduction (disproportionation) to form alcohol and carboxylic acid salt. 𝐶𝑜𝑛𝑐. 𝐾𝑂𝐻 2 HCHO → CH3-OH + H-COOK ii) Esterification: Carboxylic acids when heated with alcohols or phenols in the presence of conc. H2SO4 or HCl gas, we get esters. 𝐻+ R-COOH + R’OH → R-COOR’ + H2O 9. a) Suggest a method of preparation of benzaldehyde from toluene. (1) b) Aldehydes and ketones differ in their chemical reactions. How do they react with the following? i) Tollens' reagent ii) Alcohol. (2) c) How will you convert propanoic acid into the following compounds? i) Ethane ii) Butane. (2) [March 2013] Ans: (a) (b) i) With Tollens’ reagent, aldehydes form bright silver mirror. ii) With alcohols, aldehydes form hemi-acetals and acetals. c) i) When propanoic acid is treated with NaOH, we get sodium propanoate. This on heating with soda lime, we get ethane. [Decarboxylation reaction] 𝐶𝑎𝑂/∆ CH3-CH2-COONa + NaOH → CH3-CH3 + Na2CO3 ii) When propanoic acid is treated with NaOH or KOH, followed by electrolysis, we get butane (Kolbe’s Electrolysis). 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑠𝑖𝑠 2 CH3-CH2-COOK + 2 H2O → CH3-CH2-CH2-CH3 + 2KOH + H2 + 2CO2 10. a) Among formaldehyde, acetaldehyde and formic acid, which compounds undergo Cannizzaro reaction? Give reason. (1½ ) b) What is esterification? (1) c) Thionyl chloride is preferred to as the reagent to prepare acid chlorides. Why? (½) d) Write the chemical reaction to effect the transformation of sodium acetate to ethane. (1) e) Write the IUPAC names of the compounds given below. i) CH3-CH2-CO-CH3 ii) HOOC-CH2-COOH. (1) [SAY 2013] Ans: (a) Formaldehyde. In formaldehyde, there is no α-H atom. So it can undergo Cannizzaro reaction. (b) Carboxylic acids when heated with alcohols or phenols in the presence of conc. H 2SO4 or HCl gas, we get esters. Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 4  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® (c) When thionyl chloride is used, the acid chloride formed is pure. 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑠𝑖𝑠 (d) 2 CH3-COONa + 2 H2O → CH3-CH3 + 2KOH + H2 + 2CO2 [Kolbe’s electrolysis] (e) i) Butanone ii) Propane-1,3-dioic acid 11. a) Aldol condensation reaction is a special reaction of aldehydes. i) What is aldol condensation reaction? (1) ii) Write the structural formula of aldol formed from ethanal (1) b) Write simple chemical tests and observations used to distinguish between the following compounds: i) Propanal and propanone (1) ii) Phenol and benzoic acid (1) c) Write the names of the reagents used to bring about the following transformations i) C6H5 COCl → C6H5 CHO ii) CH3 COOH → CH2Cl-COOH (1) [March 2014] Ans: (a) (i) Aldehydes having at least one α-hydrogen atom when heated with dilute alkali, we get α,β- unsaturated aldehyde. This reaction is called Aldol condensation. 𝑑𝑖𝑙. 𝑁𝑎𝑂𝐻 2CH3-CHO → CH3-CH(OH)-CH2-CHO CH3-CH=CH-CHO Ethanal 3-Hydroxybutanal (aldol) But-2-enal (Crotanaldehyde) (ii) CH3-CH-CH2-CHO OH (b) i) Tollens’ test. When heated with Tollens’ reagent propanal gives a bright silver mirror. ii) Reaction with NaHCO3. Benzoic acid gives brisk effervescence of CO2 on treating with NaHCO3. (c) i) H2 in presence of Pd supported on BaSO4. [Rosenmund’s reduction] ii) Cl2 in presence of red P [HVZ Reaction] 12. a) Methanal (HCHO) is an aldehyde having no α-hydrogen atom. What are the products formed when methanal is treated with strong KOH solution? (1) b) How are the following conversions achieved? i) Benzoyl chloride (C6H5 COCl) to benzaldehyde (C6H5-CHO) ii) Acetic acid (CH3COOH) to chloroacetic acid (CH2Cl-COOH) iii) Benzene to Benzaldehyde iv) Ethanal (CH3-CHO) to Ethane (CH3-CH3) (1 X 4 = 4) [SAY 2014] Ans: (a) Methanol (CH3-OH) and potassium formate (HCOOK) 𝐶𝑜𝑛𝑐. 𝐾𝑂𝐻 2 HCHO → CH3-OH + H-COOK (b) i) Rosenmund’s reduction: ii) HVZ Reaction: (𝑖) 𝐶ℎ𝑙𝑜𝑟𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (𝑖𝑖) 𝐻2 𝑂 CH3-COOH → CH2Cl-COOH + HCl Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 5  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® iii) Gattermann – Koch reaction: 𝑍𝑛 𝑎𝑚𝑎𝑙𝑔𝑎𝑚/𝐶𝑜𝑛𝑐.𝐻𝐶𝑙 iv) Clemmensen reduction: CH3-CHO + [H] → CH3-CH3 13. Aldehydes, Ketones and Acids contain >C=O group. a) Name the product obtained by the reaction between acetic acid and ethanol. (1) b) (i) Give any two tests to distinguish between aldehydes and ketones. (2) (ii) Two chemical reactions are given below: (1) Identify the products of each reaction. (2) Give the name of each reaction. CH3 𝑍𝑛/𝐻𝑔 & 𝐶𝑜𝑛𝑐.𝐻𝐶𝑙 C=O → CH3 𝐶𝑂 + 𝐻𝐶𝑙 → an. AlCl3 or CuCl (2) [March 2015] Ans: (a) Ethyl acetate or ethyl ethanoate [CH3-COOC2H5] (b) (i) Tollens’ test and Fehling’s test (ii) (1) Propane [CH3-CH2-CH3] Benzaldehyde [C6H5-CHO] (2) Clemmensen reduction and Gattermann-Koch Reaction 14. a) Explain aldol condensation taking CH3-CHO as example. (2) b) Write the named reactions involved in the following conversions: 𝐻2 /𝑃𝑑 −𝐵𝑎𝑆𝑂4 i) CH3-CO-Cl → CH3-CHO 𝐶𝑜𝑛𝑐. 𝑁𝑎𝑂𝐻 ii) 2 HCHO → HCOONa + CH3-OH (1) c) How are the following conversions achieved? i) CH3-CN → CH3-COOH ii) CH3-COOH → CH2Cl-COOH (2) [SAY 2015] Ans: (a) Refer the answer of Question no. 11 (a) (b) i) Rosenmund’s reduction ii) Cannizzaro’s reaction 𝐻2 𝑂/𝐻 + (c) i) CH3-CN → CH3-COOH (𝑖) 𝐶ℎ𝑙𝑜𝑟𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (𝑖𝑖) 𝐻2 𝑂 ii) CH3-COOH → CH2Cl-COOH 15. Aldehydes, Ketones and Carboxylic acids are Carbonyl compounds. a) Aldehydes differ from Ketones in their oxidation reactions. Illustrate with one example. (1) b) How will you prepare benzaldehyde by Gatterman-Koch reaction? (1) Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 6  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® c) Write the reactions of carboxylic acid with the following reagents. (Write the chemical equations) (i) Thionyl chloride (SOCl2) (ii) Chlorine in presence of small amount of red phosphorous. (iii) Lithium Aluminium hydride (LiAlH4)/ether. (3) Ans: (a) Aldehydes readily undergo oxidation and form carboxylic acid. Ketones when oxidised using strong oxidising agent undergo C-C bond cleavage and form a mixture of carboxylic acids. (b) Benzene when treated with CO and HCl in the presence of anhydrous aluminium chloride or cuprous chloride, we get benzaldehyde. (c) (i) R-COOH + SOCl2 → R-COCl + SO2 + HCl (𝑖) 𝐶ℎ𝑙𝑜𝑟𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (𝑖𝑖) 𝐻2 𝑂 (ii) R-CH2-COOH → R-CHCl-COOH 𝐿𝑖𝐴𝑙𝐻4 /𝑒𝑡ℎ𝑒𝑟 (iii) R-COOH → R-CH2-OH 16. a) Write a test to distinguish between aldehydes and ketones. (1) b) How will you prepare benzaldehyde by Etard's reaction? (1) c) How will you bring about the following conversions? (Write the chemical equations) (i) Ethanol → Ethanoic acid (ii) Benzamide → benzoic acid (iii) Benzaldehyde → meta nitrobenzaldehyde (3) [March 2016] Ans: (a) Tollens’ test (b) When toluene is oxidised using chromyl chloride (CrO2Cl2) in CS2 followed by hydrolysis (acidification), we get benzaldehyde. This reaction is called Etard reaction. 𝐾2 𝐶𝑟2 𝑂7 /𝐻 + (c) (i) CH3-CH2-OH → CH3-COOH ethanol ethanoic acid ii) Benzamide Benzoic acid iii) Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 7  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® 17. Aldehydes and ketones are the compounds having >C = O group. a) Choose the IUPAC name of the compound CH3-CH = CH-CHO (i) Propen-1-al (ii) But-2-en-1-al (iii) Butanal (iv) But-2-en-2-al (1) b) Complete the following reactions: ∆ (i) HCHO + conc. KOH → 𝑑𝑖𝑙. 𝑁𝑎𝑂𝐻 (ii) CH3-CHO → (iii) CH3-CHO + H2N-NH2 → 𝑍𝑛/𝐻𝑔 & 𝑐𝑜𝑛𝑐.𝐻𝐶𝑙 (iv) C6H5COCH3 → (4) Ans: (a) But-2-en-1-al (b) ∆ (i) HCHO + conc. KOH → CH3-OH + HCOOK 𝑑𝑖𝑙. 𝑁𝑎𝑂𝐻 (ii) CH3-CHO → CH3-CHOH-CH2-CH3 (iii) CH3-CHO + H2N-NH2 → CH3-CH=N-NH2 𝑍𝑛/𝐻𝑔 & 𝑐𝑜𝑛𝑐.𝐻𝐶𝑙 (iv) C6H5COCH3 → C6H5CH2CH3 18. Aldehydes, ketones and acids contain >C = O group. a) Choose the IUPAC name of the compound (CH3)2CH-COOH. (i) Butanoic acid (ii) Ethanoic acid (iii) 2-Methylpropanoic acid (iv) Propanoic acid (1) b) Complete the following reactions: 𝐿𝑖𝐴𝑙𝐻4 /𝑒𝑡ℎ𝑒𝑟 (i) CH3-CH2-COOH → (ii) CH3-CH2-COOH + SOCl2 → 𝐵𝑟𝑜𝑚𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (iii) CH3-CH2-COOH → 𝐻+ (iv) CH3-CH2-COOH + CH3-OH → (4) [SAY 2016] Ans: (a) 2-Methylpropanoic acid 𝐿𝑖𝐴𝑙𝐻4 /𝑒𝑡ℎ𝑒𝑟 (b) (i) CH3-CH2-COOH → CH3-CH2-CH2OH (ii) CH3-CH2-COOH + SOCl2 → CH3-CH2-COCl 𝐵𝑟𝑜𝑚𝑖𝑛𝑒/𝑅𝑒𝑑 𝑃 (iii) CH3-CH2-COOH → CH3-CHBr-COOH 𝐻+ (iv) CH3-CH2-COOH + CH3-OH → CH3-CH2-COOCH3 19. a) The product obtained when benzene is treated with carbon monoxide and hydrogen chloride in presence of anhydrous AlCl3 is: i) Chlorobenzene ii) Phenol iii) Benzaldehyde iv) Benzoic acid (1) b) How will you carry out the following conversions? (iii) CH3-CH2-COOH → CH3-CH2-CH2-OH Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 8  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® (IV) CH3-COOH → CH3-CO-O-CO-CH3 (acetic anhydride) (4) [March 2017] Ans: (a) (iii) Benzaldehyde (b) (i) Toluene when heated with alkaline KMnO4 followed by acidification, we get benzoic acid. (ii) Benzoic acid when heated with NH3, we get benzamide. (iii) Propanoic acid when reduced using LiAlH4, we get 1-propanol. 𝐿𝑖𝐴𝑙𝐻4 /𝑒𝑡ℎ𝑒𝑟 CH3-CH2 -COOH → CH3-CH2-CH2 –OH (iv) Acetic acid when heated with Conc. H2SO4 or P2O5, we get acetic anhydride. 𝐶𝑜𝑛𝑐. 𝐻2 𝑆𝑂4 /∆ CH3-COOH → CH3-CO-O-CO-CH3 20. Explain the following: i) Esterification ii) Tollen’s test iii) HVZ reaction iv) Decarboxylation of carboxylic acid (4) [March 2017] Ans: (i) Esterification: Carboxylic acids when heated with alcohols or phenols in the presence of a mineral acid like concentrated H2SO4 or HCl gas, we get esters. Or the equation: 𝐻+ R-COOH + R’OH → R-COOR’ + H2O (ii) Tollen’s test: When an aldehyde is heated with Tollens’ reagent, we get a bright silver mirror. Or the equation: R-CHO + 2[Ag(NH3)2]+ + 3OH– → R-COO– + 2 Ag + 2 H2O + 4 NH3 (iii) HVZ reaction: Carboxylic acids having an α-hydrogen atom, when treated with halogen (chlorine or bromine) in the presence of red phosphorus, we get α-halocarboxylic acids. This reaction is known as Hell-Volhard-Zelinsky(HVZ) reaction. Or the equation: (iv) Decarboxylation of carboxylic acid: When sodium salt of carboxylic acid is heated with sodalime (a mixture of NaOH and CaO), we get alkanes. Or the equation: 𝐶𝑎𝑂/∆ R-COONa + NaOH → R-H + Na2CO3 21. a) Which among the following reduces Tollen’s reagent? i) Methanal ii) Propanone iii) Benzophenone iv) Acetophenone (1) b) Since both aldehydes and ketones possess carbonyl functional group, they undergo similar chemical reactions. i) Explain the structure of carbonyl group. (2) ii) Explain aldol condensation with an example. (2) [SAY 2017] Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 9  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® Ans: (a)Methanal (b) i) The carbonyl carbon atom is sp2-hybridised and forms three sigma (σ) bonds. The fourth valence electron of carbon forms a π-bond with oxygen. In addition, the oxygen atom also has two non bonding electron pairs. Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the π-electron cloud is above and below this plane. ii) Refer the answer of the question no. 11 (a) 22. a) Which among the following does not give red precipitate with Fehling’s solution? i) Ethanal ii) Propanal iii) Butanal iv) Benzaldehyde (1) b) How will you bring about the following conversions? i) Toluene to Benzaldehyde ii) Benzoic acid to Benzamide (2) c) Explain Cannizaro reaction with an example. (2) Ans: (a) Benzaldehyde (b) i) By Etard’s reaction ii) Benzoic acid reacts with NH3 to form ammonium benzoate which on heating to form benzamide. c) Refer the answer of the question no. 6 (d) 23. Aromatic aldehydes undergo electrophilic substitution reactions. Write the nitration reaction of benzaldehyde with chemical equation. (2) Ans: 24. Briefly describe Gattermann Koch reaction. (2) Ans: Refer the answer of the question no. 12 (b) 25. How would you account for the followings : a) Aldehydes are more reactive than ketones towards nucleophilic addition reaction. b) Boiling point of aldehydes is lower than alcohols. c) Addition reaction of sodium hydrogen sulphite is useful for the separation and purification of aldehydes. (3x1 =3) [March 2018] Ans: (a) Due to electronic effect and steric effect. (b) Due to the absence of intermolecular hydrogen bonding in aldehydes. (c) Since the product obtained is water soluble and can be converted back to the original aldehyde by treating with dil. acid or alkali. Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 10  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® 26. Identify A and B in the following equations : (2) Ans: (a) A is CH3-OH and B is HCOOK (b) A is CH3-CHOH-CH2-CH3 and B is CH3-CH=CH-CH3 27. How the conversion of carbon dioxide to carboxylic acid can be effected using Grignard reagent? (2) Ans: CO2 reacts with Grignard reagent in dry ether followed by hydrolysis, we get carboxylic acid. 28. How the conversion of an aldehyde to acetal can carry out? (Write chemical equations) (3) [SAY 2018] Ans: Aldehyde reacts with alcohol in the presence of dry HCl to give hemiacetal (alkoxyalcohol), which further react with one molecule of alcohol to give a gem-dialkoxy compound known as acetal. 29. Identify the products and give the name of the following reaction : 𝐶𝑜𝑛𝑐. 𝑁𝑎𝑂𝐻/∆ C6H5-CHO → Products (2) 𝐶𝑜𝑛𝑐. 𝑁𝑎𝑂𝐻/∆ Ans: C6H5-CHO → C6H5-CH2OH + C6H5-COONa The reaction is known as Cannizzaro reaction. 30. Explain Haloform reaction. (2) Ans: Compounds having CH3-CO- group or CH3-CHOH- group, when treated with sodium hypohalite or halogen in presence of NaOH, we get a haloform (CHX3). This reaction is called haloform reaction. 𝑁𝑎𝑂𝑋 𝑂𝑟 𝑋2 & 𝑁𝑎𝑂𝐻 R-CO-CH3 → R-COONa + CHX3 (where X = Cl, Br or I) 31. Identify A, B and C in the following sequence of reactions : ∆ H3 O + 𝐵𝑟2 /𝑅𝑒𝑑 𝑃 CH3COOH + NH3 → CH3COO-NH4+ → A→ B→ C (3) [March 2019] Ans: A = CH3-CONH2, B = CH3-COOH and C= CH2Br-COOH 32. Describe the following with equations : (a) Etard reaction (b) Aldol condensation (4) [SAY 2019] Ans: Refer the answer of the question numbers 11 (a) and 16 (b) 33. Among the following which is more acidic? (a) HCOOH b) CH3CH2COOH (c) CH3COOH (d) CH3CH2CH2COOH (1) Ans: HCOOH 34. Give a chemical test to distinguish between propanal and propanone. (2) Ans: Propanal (being an aldehyde) gives the following tests: i) Tollen’s test: When heated with Tollen’s reagent, Propanal gives a bright silver mirror ii) Fehling’s test: When heated with equal volume of Fehling’s solutions A and B, Propanal gives reddish brown ppt. Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 11  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® iii) Schiff’s test: Propanal restore the pink colour of Schiff’s reagent. The above tests are not answered by propanone (being a ketone). Iodoform (Haloform) Test: Propanone gives an yellow ppt, when treated with sodium hypoiodite or I2 in presence of NaOH. Propanal does not give this test. [Only one test is required] 35. Explain the following reactions: (a) Rosenmund reduction (b) Cannizzaro reaction. (2 x 2 = 4) [March 2020] Ans: (a) Rosenmund reduction : Acid chlorides react with hydrogen in presence of Pd supported on BaSO4, we get aldehydes. This reaction is called Rosenmund’s reduction. 𝑃𝑑/𝐵𝑎𝑆𝑂4 R-COCl + H2 → R-CHO + HCl (b) Refer the answer of the question numbers 6 (d) 36. In Etard reaction, benzaldehyde can be prepared by the oxidation of toluene by ________. (a) KMnO4 (b) K2Cr2O7 (c) CrO2Cl2 (d) CrO3 (1) Ans: CrO2Cl2 37. CO + HCl X Anhydrous AlCl3/CuCl (a) Identify the Product X (1) (b) Name the reaction. (1) Ans: (a) Benzaldehyde [C6H5-CHO] (b) Gattermann Koch reaction 38. (a) Give a chemical test to distinguish aldehydes from ketones. (1) (b) Carbonyl group (>CO) of aldehydes and ketones can be reduced to CH2 group in Clemmensen reduction. Name the reagent used. (1) Ans: (a) Tollens’ test (b) Zinc amalgam and Conc. HCl. 39. With the help of chemical reaction explain the following name reactions: (a) Aldol condensation (b) HVZ reaction (2 x 2 = 4) [SAY 2020] Ans: (a) Refer the answer of the question no. 11 (a) (b) Refer the answer of the question no. 20 (iii) 40. (i) The test to distinguish Propanal and Propanone is …………. (A) Tollens' test (B) Lucas test (C) Hinsberg test (D) Bromine-Water test (1) (ii) Which is more reactive towards nucleophilic addition, CH3CHO or C6H5-CHO? Give reason. (2) Ans: (i) Tollens’ test (ii) CH3-CHO C6H5-CHO (Benzaldehyde) is less reactive because of the less electrophilicity of the carbonyl carbon due to resonance. Or, due to the presence of bulky phenyl group (steric hindrance). 41. Identify the products and name the reactions. 𝐶𝑜𝑛𝑐. 𝐾𝑂𝐻 (i) HCHO → ………………….. (1) 𝑑𝑖𝑙. 𝑁𝑎𝑂𝐻 (ii) CH3CHO → ………………….. (1) Ans: (i) CH3-OH (methanol) and H-COOK (Potassium formate) (ii) CH3-CH(OH)-CH2-CHO (3-Hydroxybutanal) Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 12  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® 42. (i) How will you prepare Benzaldehyde from the following: A. Toluene B. Benzene C. Benzoyl chloride (3) (ii) Identify the product obtained when Acetic acid is heated with P2O5. (1) [March 2021] Ans: (i) Refer the answer of the question no. 12 (b) and 22 (b) (ii) Ethanoic anhydride or acetic anhydride or (CH3-CO)2O 43. A compound is converted into ‘2-Chloropropanoic acid’ by HVZ reaction. Identify the compound and the reagent used. (2) Ans: CH3-CH2-COOH (Propanoic acid). Reagent used is Cl2 in presence of Red Phosphorus. 44. (i) Write the IUPAC name of CH3CHO. (1) (ii) Give two methods for the conversion R-CN into R-CHO. (2) (iii) Identify the class of product formed when HCN is added to an aldehyde or ketone. (1) Ans: (i) Ethanal (ii) (a) By reduction using stannous chloride (SnCl2) in the presence of hydrochloric acid followed by acidification [Stephen reaction] (b) By reduction using diisobutylaluminium hydride (DIBAL-H) to imines followed by hydrolysis. (iii) Cyanohydrin 45. Explain the following : (i) Tollens’ reagent test. (2) (ii) Gatterman-Koch reaction. (2) [SAY 2021] Ans: (i) Refer the Answer of Question number 6 (c) (ii) Refer the Answer of Question number 15 (b) 46. (i) Write the products of the following reaction : (2) (ii) Explain Hell – Volhard – Zelinsky (HVZ) reaction. (2) (iii) Suggest a suitable method for the following conversion : (2) [March 2022] Ans: (i) CH3-OH(Methanol) + HCOONa (Sodium formate) (ii) Refer the Answer of Question number 20 (iii) (iii) When toluene is oxidised using chromyl chloride (CrO2Cl2) in CS2 followed by hydrolysis (acidification), we get benzaldehyde. This reaction is called Etard reaction. OR, Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 13  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® By treating toluene with chromic oxide in acetic anhydride, followed by acidification. OR, By Side chain chlorination of toluene followed by hydrolysis gives benzaldehyde. 47. (i) Predict A and B (2) (ii) Suggest a test to distinguish aldehydes and ketones. (1) Ans: (i) A is CH3-CH2-CH2-OH (Propan-1-ol or Propyl alcohol) and B is CH3-CH2-CHO (Propanal or Propionaldehyde) (ii) Fehling’s test or Tollen’s test or Benedict’s test. 48. (i) “Acyl chlorides can be reduced to give corresponding aldehydes.” Give the name of the reaction and catalyst used in the reaction. (2) (ii) Distinguish between Aldol condensation and Cannizzaro reaction. (Any two differences) (2) (iii) Among the following which is more acidic? Monochloroacetic acid or Monofluoroacetic acid? Justify your answer. (2) [SAY 2022] Ans: (i) Rosenmund’s Reduction. Catalyst used is Pd supported on BaSO4 (ii) Aldol Condensation Cannizzaro reaction Given by aldehydes or ketones having atleast one α Given by aldehydes having no α hydrogen atom. hydrogen atom. Reagent used is dil. alkali Reagent used is conc. alkali The product formed is α,β-unsaturated aldehyde or The product formed is alcohol and salt of ketone. carboxylic acid. (iii) Monofluoro acetic acid. This is because of the greater electron withdrawing inductive effect of fluorine. 49. Identify the product ‘X’ in the chemical reaction given below: (1) Ans: Benzaldehyde (C6H5-CHO) [Rosenmund’s reduction] 50. (i) Write any two nucleophilic addition reactions of aldehyde. (2) (ii) Name the product formed when ethanal is reduced with LiAlH4. (1) Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 14  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® Ans: (i) Aldehydes undergo nucleophilic addition reaction with HCN and form cyanohydrins. 𝑂𝐻 − OR, R-CHO + HCN → R-CHOH-CN Aldehydes add alcohols to form hemi-acetals and acetals. 𝐻𝐶𝑙 OR, R-CHO + R-OH → R-CH(OH)-OR → R-CH(OR)2 (ii) Ethanol or Ethyl alcohol [CH3-CH2-OH] 51. (i) Which one is more reactive among aldehydes and ketones ? (1) (ii) Describe any two tests to distinguish aldehydes from ketones. (2) Ans: (i) Aldehydes (ii) (a) Tollen’s test: When an aldehyde is heated with Tollens’ reagent, we get a bright silver mirror. (b) Fehling’s test: When an aldehyde is heated with equal volume of Fehling’s reagent A (aqueous solution of CuSO4) and B (alkaline sodium potassium tartarate), we get a red precipitate of cuprous oxide (Cu2O). These tests are not answered by ketones. 52. (i) Explain Haloform reaction. (2) (ii) How will you prepare benzaldehyde by Gattermann – Koch reaction ? (1) (iii) Write the name of the reaction involved in the following conversion : 𝑍𝑛− 𝐻𝑔 & 𝐶𝑜𝑛𝑐.𝐻𝐶𝑙 CH3 – CO – CH3 → CH3 – CH2 – CH3 + H2O (1) [March 2023] Ans: (i) Refer the answer of the question number 30. (ii) Refer the answer of the question number 15 (b). (iii) Clemmensen reduction 53. Name the product obtained when Toluene is treated with CrO2Cl2 in presence of CS2. (a) Benzaldehyde (b) Benzoic acid (c) Phenol (d) Chlorobenzene (1) Ans: Benzaldehyde 54. (i) Give a test to distinguish aldehydes from Ketones. (1) (ii) What is the reagent used in Clemmensen’s reduction ? (1) (iii) Describe Hell-Volhard-Zelinsky Reaction. (1) Ans: (i) Refer the answer of the question number 51 (ii) (ii) zinc amalgam and conc. HCl (iii) Refer the answer of the question number 20 (iii) 55. Identify the products X and Y in the following reactions. Also name these reactions. (1½) (1½) Ans: (i) Benzaldehyde [Gattermann Koch Reaction] (ii) Benzaldehyde [Rosenmund’s reduction] 56. (i) Name the product obtained when ethanal reacts with dilute NaOH. Write the chemical equation for the above reaction. (2) (ii) What is the effect of substituents on the acidity of carboxylic acids ? (2) [SAY 2023] Ans: (i) 3-Hydroxybutanal [CH3-CH(OH)-CH2-CHO] Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 15  Join Now: https://join.hsslive.in Downloaded from https://www.hsslive.in ® 𝑑𝑖𝑙. 𝑁𝑎𝑂𝐻 2CH3-CHO → CH3-CH(OH)-CH2-CHO Ethanal 3-Hydroxybutanal (ii) Electron withdrawing groups increase the acidity of carboxylic acids by stabilising the carboxylate ion. While electron donating groups decrease the acidity by destabilising the carboxylate ion. 57. (i) What is Tollens’ reagent ? (1) (ii) Which among CH3CHO and CH3COCH3 form a silver mirror on reaction with Tollens’ reagent ? (1) Ans: (i) Tollen’s reagent is Ammoniacal silver nitrate (AgNO3) (ii) CH3-CHO [Tollen’s test is answered by aldehydes only.] 58. (i) An organic compound A on reaction with CrO2Cl2 in CS2 followed by acidification gives benzaldehyde as a product. Identify the compound A and also name the reaction. (2) (ii) What is the product obtained when the above organic compound A undergoes side chain oxidation with acidic potassium permanganate ? (1) Ans: (i) A is Toluene (C6H5-CH3). The rection is Etard reaction. (ii) Benzoic acid (C6H5-COOH) 59. Describe the following reactions: (i) Cannizaro reaction (ii) Stephen reaction (4) [March 2024] Ans:(i) Refer the answer of the question no. 6(d) (ii) Nitriles when reduced using stannous chloride and HCl followed by hydrolysis give aldehydes. This reaction is known as Stephen reaction. 𝐻3 𝑂 + OR, RCN + SnCl2 + HCl → R-CH=NH → R-CHO 60. Describe any one chemical test to distinguish between aldehydes and ketones. (2) Ans: Tollens Test: Aldehydes form bright silver mirror when heated with Tollens’ reagent. 61. Explain the following: (i) Aldol condensation (ii) Rosenmund’s reaction (3) Refer the answer of the question numbers 11 (a) and 35 (a) 62. (i) Explain HVZ reaction. (2) (ii) Arrange the following acids in the increasing order of their acidic character : (2) [SAY 2024] (i) Refer the answer of the question no. 20 (ii) (ii) CH3-COOH < H-COOH < %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Aldehydes, Ketones and Carboxylic Acids – Prepared by Anil Kumar K L, PHSS Vandiperiyar Page 16