Q.1 What is rectified spirit ?
Answer: A mixture of 95% ethyl alcohol and 5% water is called rectified spirit.
Q.2 Name the alcohol used for polishing wooden furniture.
Answer: Ordinary spirit.
Q.3 Which type of alcohol is formed by hydroboration oxidation of unsymmetrical alkene?
Answer: In case of hydro oration oxidation of alkene the alcohol formed is (primary alcohol) opposite to Markovnikov's rule.
Q.4 Among acids and esters which can be reduced to alcohol easily by catalytic hydrogenation?
Answer: Esters can be easily reduced to alcohols.
Q.5 Name the product formed by reaction of Grignard's reagent with an aldehyde followed by hydrolysis.
Answer: Alcohol (1°alcohol with methanal and 2° alcohol with other aldehydes).
Q.6 Which one has higher boiling point propane or ethanol?
Answer: Ethanol has higher boiling point than propane.
Q.7 Alcohols act as weak acid. Why?
Answer: Due to polar nature of O - H bond alcohol acts as weak acid.
Q.8 Which type of alcohol does not react with Lucas reagent at room temperature?
Answer: 1° alcohol does not react with Lucas reagent at room temperature.
Q.9 What is the rate of reactivity of 1°, 2° and 3° alcohols with hydrogen halide?
Answer: 3° > 2° > 1°. (Reactivity of hydrogen halide)
Q.10 What is the ease of dehydration of 1 °, 2° and 3° alcohols?
Answer: 3° > 2° > 1°. (Ease of dehydration of alcohol)
Q.11 What is wood spirit?
Answer: Methanol is also known as wood spirit.
Q.12 Which enzyme catalyses conversion of sucrose to ethanol?
Answer: Invertase followed by zymase.
Q.13 What is the main use of ethanol?
Answer: Solvent in paint industry.
Q.14 Explain denaturation.
Answer: The process of making alcohol unfit for drinking is called denaturation.
Q.15 Which compound is mixed in ethanol for denaturation?
Answer: Copper sulphate and pyridine.
Q.16 Which alcohol on oxidation gives aldehyde?
Answer: 1° alcohol on oxidiation gives aldehyde.
Q.17 Which alcohol on oxidation gives ketone?
Answer: 2° alcohol on oxidation gives ketone.
Q.18 What are phenols?
Answer: When the hydrogen atom is replaced by -OH group in benzene ring the compound obtained is called phenol.
Q.19 What is carbolic acid?
Answer: Phenol is also called carbolic acid.
Q.20 Phenols are acidic. Why?
Answer: Due to presence of polar -OH group phenol behaves as acid and phenoxide ion is more stable.
Q.21 What is the hybridisation of oxygen atom in ether?
Q.22 Boiling points of ethers are much lower than that of alcohols. Why?
Answer: Ethers do not form H-bonding due to which they have lower boiling points than corresponding alcohols.
Q.23 Boiling points of alcohols are higher than correspond in hydrocarbons, ethers and alkyl halides. Why?
Answer: The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding in them which is lacking in ethers, hydrocarbons and alkyl halides.
Q.24 Boiling points of alcohols decrease with increase in branching of carbon chains. Why?
Answer: As the branching increases surface area decreases and hence magnitude of Van der Waals force also decreases so, boiling point decreases.
Q.25 Boiling points of ethanol is much higher than methoxy methane. Why?
Answer: Ethanol has high boiling point than methoxy methane because alcohols are soluble in water due to formation of H-bonding with water molecule.
Q.26 Solubility of alcohols in water decreases with increasing size of alkyl group. Why?
Answer: Alkyl groups are hydrophobic in nature. So, as size of alkyl group increases, its solubility in water decreases.
Q.27 What is the chief use of methanol?
Answer: Methanol is chiefly used for the preparation of formaldehyde.
Q.28 Which alcohol is highly poisonous?
Answer: Methanol is highly poisonous.
Q.29 What is the advantage of using PCC for the oxidation of alcohols?
Answer: Oxidation stops at aldehyde level.
Q.30 Phenols are more reactive than benzene towards electrophilic substitution reaction. Why?
Answer: Resonating structures show that benzene ring acquires -ve charge which implies that there is a greater electron cloud. Therefore, an electrophile readily attacks at o/p position of phenol than in benzene.
Q.31 Anisole undergoes bromination with bromine and ethanoic acid even in absence of iron bromide catalyst. Why?
Answer: Anisole undergoes bromination with bromine and ethanoic acid even in absence of iron (III) bromide catalyst due to activation of benzene ring by the methoxy group.
Q.32 What are the conditions for preparation of ethers from alcohols?
Answer: Conditions for the preparation of ethers from alcohols are : (i) only 1° alcohol should be taken. (ii) alkyl should be unhindered. (iii) temperature should be kept low.
Q.33 Why is it difficult to prepare ethyl methyl ether by dehydration of alcohols?
Answer: For the preparation of ethyl methyl ether two different types of alcohols are needed. As a result a mixture products is formed which is difficult to separate.
Q.34 What are the advantages of Williamson's method.
Answer: (i) Both symmetrical and unsymmetrical ethers can be prepared by this method. (ii) 2° and 3° ethers can also be prepared by this method
Q.35 Why is Williamson's synthesis not applicable to tertiary halides?
Answer: In case of secondary or tertiary alkyl halides elimination competes over substitution and product formed is alkene.
Q.36 Tertiary alcohols are easiest to dehydrate, why?
Answer: During the process of dehydration the intermediate formed is carbocation. We know that 3°-carbocation is most stable carbocation. So, it is easiest to dehydrate 3°-alcohol.
Q.37 How is phenol obtained from cumene?
Answer: In alcohols, -OH group is attached to electron releasing alkyl group which decreases polarity of O-H bond while in phenols -OH group is attached to electron withdrawing phenyl group which increases polarity of O - H bond.
Q.38 What is denatured alcohol?
Answer: Ethanol, when mixed with copper sulphate (to give it colour) and pyridine (a foul smelling liquid) is called denatured alcohol. It affects judgements and lowers inhibition and also cause nausea and loss of consciousness. Ethanol oxidises to ethanoic acid which is the cause of diseases.
Q.39 Why is fermentation carried out in absence of air?
Answer: If air gets into fermentation mixture, it oxidises ethanol to ethanoic acid which destroy the taste of alcoholic drinks.
Q.40 What is the order of reactivity of alcohols in case of esterification?
Answer: Rate of esterification: 1° > 2° > 3° alcohol.
Q.41 Alcohols can act both as acids and bases. Explain.
Answer: Alcohols can act as acids in strongly basic medium by releasing H+ion. Similarly, they can act as Lewis bases in the acidic medium.
Q.42 Sodium metal cannot be used for drying alcohols. Assign reason.
Answer: Sodium metal reacts with alcohol to evolve hydrogen gas. Moreover, it also catches fire in hatr. Therefore, it can not be used for drying alcohol.
Q.43 Ethyl alcohol and dimethyl ether are isomeric but alcohol is a liquid at room temperature while ether is a gas. Explain.
Answer: Ethyl alcohol molecules are associated due to intermolecular hydrogen bonding but the same is not present in the molecules of dimethyl ether. As a result of association, ethyl alcohol is a liquid at room temperature while dimethyl ether is a gas.
Q.44 At room temperature tertiary alcohols form white turbidity very fast with Lucas reagent while primary alcohols do not. Give reason.
Answer: A carbocation intermediate is formed when HCl(g) reacts with an alcohol in the presence of anhydrous ZnCl2(dehydrating agent). Since tertiary carbocation is very stable while primary carbocation is rather unstable therefore, tertiary alcohols react very fast with Lucas reagent to form white turbidity immediately while the primary alcohols do not react at room temperature.
Q.45 Predict the product of the reaction between HBr and but-2-en-l-ol.
Q.46 Hydration of 3-phenylbut-l-ene in dilute H2SO4 forms 2-phenylbutan-2-ol and not 3-phenylbutan-2-ol. Why?
Answer: The secondary carbocation initially formed as a result of hydration changes to a more stable tertiary carbocation by H− ion shift. Therefore, the final product is different from the expected product.
Q.47 On reacting tertiary butyl alcohol and normal butyl alcohol separately with a few drops of dilute KMnO4,purple colour disappears and a brown precipitate is formed only in one case. Which of the two alcohols will respond to the reaction?
Answer: Only n-butyl alcohol is oxidised under the reaction conditions while tertiary butyl alcohol fails to react.
Q.48 3, 3-Dimethyl butan-2-ol loses a molecule of water in the presence of concentrated sulphuric acid to give tetramethylethylene as the major product. Suggest a suitable mechanism.
Q.49 What is the structure of the major product when 3-Ethylpent-2-ene is reacted with Hg(OAc)2/H2O;NaBH4?
Answer: The reaction is known as oxymercuration-demercuration and proceeds as follows :
Q.50 p-nitrophenol is a stronger acid than phenol while p-cresol is a weaker acid. Discuss.
Answer: The −NO2 group is an electron withdrawing group. When present at the para position in the ring, it decreases the electron density on the oxygen atom of O?H group due to conjugation and the release of H+ ion becomes easier than in phenol. On the other hand, −CH3 group is an electron releasing group. It increases the electron density on the oxygen atom and the release of H+ ion becomes difficult compared to phenol. Therefore, p-nitrophenol is a stronger acid than phenol while p-cresol is a weaker acid. For further details, consult section 12.16 (Chemical properties of phenols).