CHEMISTRY – TEST – 5 – ETHER, ALCOHOLS AND PHENOL (THEORY) (50 min.) (Candidates are allowed additional 10 minutes for only reading the paper They must NOT start writing during this time) All questions are compulsory Question 1 is of 10 marks having three sub parts all of which are compulsory. Question numbers 2 - 4 carry 2 marks. Question numbers 5 -7 carry 3 marks. Question numbers 8 carry 5 marks. The intended marks for questions or part of questions are given in brackets [ ]. Balanced equations must be given wherever possible and diagrams where they are helpful. When solving numerical problems, all essential working must be shown. In working out problems, use the following data: Gas constant R = 1.987 cal deg -1mol -1 = 8.314 JK -1 mol-1 = 0.0821 dm 3 atm K -1 mol -1 3 1 l atm = 1 dm atm = 101.3 J 1 Faraday = 96540 coulombs

NAME

SCHOOL

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MOB. (PARENT –1)

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M. M. 30

Question 1: [A] Choose the most appropriate word to complete the following statement. [3] 3 2 [more, less, phenol, phenoxide ion, sp , sp ,aldehyde, carboxylic acid, same, different ] (i) The primary alcohols on oxidation give first to _______________ and then to ____________________ having _____________ number of carbon atoms. (ii) The hydroxyl group is attached to _______________hybridized carbon atom of an alcohol (iii) Phenols are _____________ acidic than alcohol due to greater resonance stabilization of ____________. Ans: (i) aldehyde, carboxylic acid, same (ii) sp

3

(iii) Methanol [B] Choose the correct alternative.

[3]

(i) When phenol is distilled with zinc dust, it gives: (a) Benzene

(b) toluene

(c) benzldehyde

(d) benzoic acid

(ii) Phenol can be distinguished from ethanol by all reagents except (a) NaOH

(b) FeCl3

(c) Br2 / H2O

(d) Na

(iii) Wood spirit is known as (a) methanol

(b) ethanol

(c) acetone

(d). benzene

Ans: (i) (a) Benzene (ii) (a) NaOH (iii) (a) methanol [C] Answer the following (i) Arrange the glycerol, ethanol and ethylene glycol according to increasing order of their Boiling point.

[4]

Ans: Ethanol < Ethylene glycol < Glycerol (ii) Phenol under goes electrophillic substitution at ortho and para position. Give reason. Ans: Phenol undergoes electrophilic substitution at ortho and para position as the –OH group attached increases the electron density at ortho and para position. (iii) Why alcohol is less acidic then phenol. Ans: Alcohol is less acidic than phenol because the alkyl group does not attract the electron strongly as the phenoxide ion. (iv) Write formula and name of trihydric alcohol.

Ans: HO – CH2 – CH(OH) – CH2 – CH2OH Butane – 1, 2, 4 - triol Question 2: Convert the following: (i) Acetone to propan-2-ol (ii) Acetone to tert butyl alcohol Ans: (i) CH3COCH3 + H2 → CH3CH(OH)CH3 + H 3O (ii) CH3COCH3 + CH3MgBr → CH3C(OMgBr)(CH3)CH3 CH3C(OH)(CH3)CH3 + Mg(OH)Br Question 3: Why nitration of phenol takes place only by dil HNO 3? Ans: Nitration of phenol takes place only by dil HNO3 because here phenol itself acts as a protonating agent OR It takes place only in the presence of HNO3 because nitronium ion id easily formed in the presence of phenol. Question 4: Sodium metal can be used for drying diethyl ether but not ethanol. Explain. Ans: Sodium metal is not used to fry ethanol because sodium reacts with it and forms sodium ethoxide. Question 5: Write the different steps of mechanism of esterification of ethanol. Ans: Step 1: Protonation of ethanoic acid O O-H CH3 – C – OH + H

+

CH3– C – OH

CH3 – C

+

[2]

[2]

[2] [3]

OH

OH

Step 2: Alcohol attacks the carbonyl group as a nucleophile OH CH3 – C

+

OH

OH

+

CH3 – C – O - C2H5

+ C2H5OH

OH H

Step 3: Oxonium ion loses a proton OH OH +

CH3 – C – O - C2H5

CH3 – C – OC2H5 + H

OH H

+

OH CH3 – C – OC2H5 + H2O

O Question 6: Distinguish chemically between the methanol and ethanol. Ans: Test Ethanol Iodoform test Yellow precipitate Oil of winter green test (Salicylic acid No reaction & few drops of conc. Sulphuric acid) Question 7: What happens when? Give chemical equation only (i) Phenol is react with dil nitric acid (ii) Phenol reacts with acetyl chloride (iii) Phenol is treated with excess aqueous bromine Ans: (i) 2C6H5OH + 2HNO3 → 2C6H4(OH)(NO2) + 2H2O (ii) C6H5OH + CH3COCl → C6H4(OH)(COCH3) + HCl

[3] Phenol No reaction Pleasant smell of methyl salicylate [3]

OH Br

Br

(iii) C6H5OH + 3Br2 →

+ 3HBr Br

Question 8: (a) How to convert following (i) Propan-2-one into 2-methyl propan-2-ol (ii) Methanol into butanol (b) What happen when? (i) 2-chloro butane is treated with aqueous solution of alkali (ii) Propene is treated with diborane followed by oxidation

[5]

(iii) Ethanol is treated with iodine in the presence of caustic soda Or Explain the following (i) Alcohols are soluble in water (ii) C-O bond length in phenol is less than that of alcohol. 0 (iii) COH bond angle in alcohol is less than tetrahedral angle of 109.5 (iv) Glycerol is more viscous then alcohols (v) Order of reactivity of HX with alcohol is HI>HBr>HCl>HF H2O Ans: (a) (i) CH3COCH3 + CH3MgBr → CH3C(CH3)(OMgBr)CH3 H+ CH3C(CH3)(OH)CH3 + Mg(OH)Br Cu tube (ii) CH3OH + [O] HCHO + H O 2 573 K H2O + HCHO + C3H7MgBr CH3CH2CH2CH2OH + Mg(OH)Br H (b) (i) CH3CH2CH(Cl)CH3 + KOH → CH3CH2CH(OH)CH3 + KCl 2O2 (ii) 3CH3CH=CH2 + BH3 → (CH3CH2CH2)3B 3H 3CH3CH2CH2OH + B(OH)3 OH (iii) C2H5OH + 4I2 + 6NaOH → CHI3 + HCOONa + 5NaI + 5H2O OR (i) Alcohols are soluble in water due to H-bonding. (ii) C-O bond length in phenol is less than that of alcohol because C-O bond has slight double bond nature due to resonance. (iii) COH bond angle in alcohol is less than tetrahedral angle of 109.5° due to the repulsion between the unshared pair of electrons in oxygen atom. (iv) Glycerol is viscous because of hydrogen bonds between the –OH groups. But glycerol has more –OH groups than the other alcohols so it is more viscous. (v) Order of reactivity of HX with alcohol follows this trend because the tendency to donate electron pair by the halogen atom decreases in the order – I > Br > Cl