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Aldehydes and Ketones: FAQs, MCOs & Answer with explanation

 

1. The carbon atom of carbonyl group is:





... Answer is b)
Explanation: Carbonyl carbon posesses trigonal planer geometry with bond angle of 120O, which is only possible when carbon is sp2 hybridized.

2. Ketones are prepared by the oxidation of





... Answer is b)
Explanation: In secondary alcohol, -OH group is bonded with that carbon that is further bonded with two carbon atoms. During oxidation of secondary alcohol, one hydrogen is removed from OH group and another hydrogen is removed from carbon atom bonded with OH group, so resultant product is a ketone.

3. Acetone reacts with HCN to form an cyanohydrins. It is an example of





... Answer is c)
Explanation: During formation of cyanohydrin, "CN-"is produced with the help of base as a catalyst. This "CN-" acts as a strong nucleophile and attacks on electrophilic carbonyl carbon, thus it is known as nucleophilic addition reaction.

4. Cannizzaro's reaction is not given by





... Answer is b)
Explanation: Aldehydes or ketones without α-hydrogen proceed with Cannizzaro's reaction. Hence acetaldehyde posses α-hydrogen, so it does not undergo Cannizzaro's reaction.

5. Which of the following reagent will react with both aldehydes and ketones?





... Answer is a)
Explanation: Tollen's reagent, Fehling's reagent and Benedict's reagent contain metallic ions which act as oxidizing agents. Ketones do not react with these reagents. Reason is that ketones do not contain hydrogen directly bonded carbonyl carbon which can be easily oxidized. .

6. Aldehydes are the oxidation product of





... Answer is a)
Explanation: When a primary alcohol is oxidized, loss of hydrogen from OH along with hydrogen from carbon containing OH group produces R1COH type aldehyde while from secondary alcohol, it produces R1COR2 type ketone. Ter. alcohol and carboxylic do not undergo oxidation.

7. Which of the following compounds will not give iodoform test on treatment with I2/NaOH





... Answer is d)
Explanation: Iodoform test is given by those aldehydes or ketones which contain acetyl (CH3CO) group or secondary alcohols which contain methyl (CH3) group and OH group bonded with same carbon atom or ethanol. Hence, among above aldehydes and ketones, only compound, 3-pentanone (CH3CH2COCH2CH3 contain acetyl group, so it will give positive iodoform test

8. Aldehydes and ketones are carbonyl compounds. Which of them reacts both with NaBH4 and with Tollen's reagent?





... Answer is b)
Explanation: Both aldehyde and ketones can be reduced with weak reducing agent such as NaBH4. However among aldehydes and ketones, only aldehydes react with with Tollen's reagent. So most suitable option is b.

9. Which one of the following can undergo aldol condensation reaction?





... Answer is b)
Explanation: Aldehydes and ketones having α- hydrogen ( a hydrogen attached with carbon directly bonded with carbonyl carbon) undergo aldol condensation. From above options, only acetaldehyde has α-hydrogen, so it will undergo aldol condensation reaction.

10. Aldol condensation is not successful with compounds?





... Answer is a)
Explanation: Aldehydes and ketones having α-hydrogen undergo aldol condensation reaction. Aldol condensation with carbonyl compounds without α-hydrogen is not feasible .

11. Phenyl hydrazine on treatment with carbonyl compounds form?





... Answer is b)
Explanation: Phenyl hydrazine on treatment with carbonyl compounds produce phenyl hydrazine.

12. Formaldehyde reacts with NH3 to give





... Answer is c)
Explanation: Formaldehyde reacts with NH3 to give hexamethylene tetraamine.

13. General formula of aldehyde and ketone is





... Answer is a)
Explanation: The formula of acetaldehyde (CH3COH) is C2H4O and for acetone (CH3COCH3) is C3H6O, so, general formula for both is CnH2nO.

14. Which of the following can be prepared in the laboratory by dry distillation of (HCOO)2Ca?





... Answer is b)
Explanation: Dry distillation of calcium format (HCOO)2Ca gives formaldehyde while Dry distillation of calcium acetate (H3COO)2Ca gives acetone. However, distillation of both gives acetaldehyde.

15. The color of iodoform is





... Answer is c)
Explanation: Floroform, chloroform, bromoform are colorless, however, iodoform is yellow crystalline solid at room temperature.  
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