(a) Write the products formed when CH3CHO reacts with the following reagents:
(i) HCN
(ii) H₂N−OH
(iii) CH₃CHO in the presence of dilute NaOH

(b) Give simple chemical tests to distinguish between the following pairs of compounds:
(i) Benzoic acid and Phenol
(ii) Propanal and Propanone

OR

(a) Account for the following:
(i) Cl−CH₂COOH is a stronger acid than CH₃COOH.
(ii) Carboxylic acids do not give reactions of the carbonyl group.

(b) Write the chemical equations to illustrate the following name reactions:
(i) Rosenmund reduction
(ii) Cannizzaro's reaction

(c) Out of CH₃CH₂−CO−CH₂−CH₃ and CH₃CH₂−CH₂−CO−CH₃, which gives iodoform test?

(i) Acetaldehyde (CH3CHO) reacts with hydrogen cyanide HCN to give 2-Hydroxypropapanenitrile as product.

(ii) Acetaldehyde (CH3CHO) reacts with Hydroxylamine (NH2OH) to give acetaldoxime as a product.

(iii) The reaction of acetaldehyde with acetaldehyde in the presence of dilute NaOH, this is the kind of Aldol reaction by which obtained 3-hydroxybutanal as a product. Further, proceed reaction when using heat in the reaction, its gives aldol condensation product which is But-2-enal.

(b) Chemical tests to distinguish the following compounds:
(i) Benzoic acid and Phenol : Benzoic acid and phenol can be distinguished by FeCl₃ tests. Both reacts with FeCl3 to give different colours. Phenol reacts with FeCl3 to give violet coloured precipitate while benzoic acid gives buff coloured precipitate.

3C₆H₅OH +FeCl₃ ---> (C₆H₅O)₃Fe + 3HCl
phenol                      violet colour

3C₆H₅COOH +FeCl₃ ---> (C₆H₅COO)₃Fe +3HCl
Benzoic acid                  buff colour

(ii) Propanal and Propanone : These two are distinguished by the iodoform test.propanal does not give iodoform test when it reacts with I₂ in the presence of NaOH while propanone give iodoform test when reacts with I2 in the presence of NaOH.

CH₃COCH₃ +3NaOI --> CHI₃ + CH₃COONa +2NaOH
Propane                  Yellow ppt
CH₃CH₂OH +NaOI ---> No ppt of CH₃I formed

Or

a) (i) Cl-CH₂COOH is a stronger acid than CH₃COOH :
Substitution of electron withdrawing group on carboxylic acid affect the acidity of the carboxylic acid. Chlorine is a electron withdrawing group and its increase the acidity of carboxylic acids by stabilising the conjugate base due to delocalisation of the negative charge by resonance effects.
Chloroacetic acid ( Cl-CH₂COOH) pKa value is equal to 2.7, while p_Ka value of acetic acid (CH₃COOH) is equal to 4.7.

(ii) In carboxylic acid presence of lone pairs of electrons on oxygen which are involves in resonance due to this the electrophilic character of carbon in carboxylic acid decreases. So due to such reason carboxylic acid does not show the characteristic reaction of the carbonyl group.

b) 
i)

ii)



C ) 

Pentan-2-one (CH₃-CH₂-CH₂-CO-CH₃) give yellow precipitate of CHI₃ with NaOI, that means it gives iodoform test.

CH₃-CH₂-CH₂-CO-CH₃ + 3NaOI --> CHI₃ + CH₃CH₂COONa + 2NaOH
                                               Yellow
                                                ppt.

Pentan-3-one (CH₃-CH₂-CO-CH₂-CH₃) does not give yellow precipitate with CHI₃ with NaOI, so Pentan-3-one does not give iodoform test.