Please refer to Alcohols, Phenols and Ethers Class 12 Chemistry Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Chemistry based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Chemistry for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.
Class 12 Chemistry Important Questions Alcohols, Phenols and Ethers
Very Short Answer Questions
Question. Write the IUPAC name of the given compound.
Answer. 2-Phenylethanol
Question. Write the equation involved in the acetylation of Salicylic acid.
Answer.
Question. Give reason for the following :
Phenol is more acidic than ethanol.
Answer. Phenols are more acidic than alcohols. It can be explained on the basis that alcohol on losing H+ ions form alkoxide ion and phenol forms phenoxide ion. The greater acidity of phenol is due to the stability of the phenoxide ion which is resonance stabilized as shown below.
On the other hand, alkoxide ion shows no such resonance stabilisation and is unstable.
Question. Write the IUPAC name of the given compound :
Answer. 2,5-Dinitrophenol
Question. Draw the structure of hex-1-en-3-ol compound.
Answer. Hex-1-en-3-ol
Question. Write the IUPAC name of the following :
Answer. 2-Bromo-3-methylbut-2-en-1-ol
Question. Give the structure and IUPAC name of the product formed when propanone is reacted with methylmagnesium bromide followed by hydrolysis.
Answer.
Question. Give a chemical test to distinguish between 2-Pentanol and 3-Pentanol.
Answer. On adding I2 and NaOH, 2-pentanol will give yellow precipitate of iodoform whereas 3-pentanol will not give yellow precipitate.
Question. Of the two hydroxy organic compounds ROH and R′OH, the first one is basic and other is acidic in behaviour. How is R different from R′?
Answer. R is alkyl group and R′ is aryl group. R must be a group having more electron density than H. i.e., having +I effect where as R′ must be having –I effect.
Question. Give reasons for the following :
Propanol has higher boiling point than that of the hydrocarbon butane.
Answer. The molecules of butane are held together by weak van der Waals forces of attraction while those of propanol are held together by stronger intermolecular hydrogen bonding.
Question. Why do phenols not give the protonation reaction readily?
Answer. Due to electron withdrawing effect of phenyl group the electron density on the oxygen atom of –OH group in phenol is less. Hence, phenols do not undergo protonation.
Question. Name a substance that can be used as an antiseptic as well as a disinfectant.
Answer. Phenol : 0.2% solution of phenol is an antiseptic while 2% solution is used as disinfectant.
Question. How would you obtain ethane-1, 2-diol from ethanol ?
Answer.
Question. How would you obtain acetophenone from phenol?
Answer.
Question. Give a chemical test to distinguish between Benzoic acid and Phenol.
Answer. Benzoic acid gives brisk effervescence of CO2 on addition of NaHCO3 while phenol does not.
Question. Give one chemical test to distinguish between the following pairs of compounds.
1-Propanol and 2-Propanol.
Answer. On adding I2 and NaOH 2-Propanol will give yellow ppt. of iodoform, whereas 1-propanol will not give yellow ppt.
Question. Write the main product(s) in the following reaction :
Answer.
Question. Explain the following giving one example :
Friedel Craft’s acetylation of anisole.
Answer. Reagents : Acetyl chloride and Lewis acid catalyst.
Question. Account for the following :
Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method.
Answer. Acid dehydration of 2° and 3° alcohols give alkenes rather than ethers. Due to steric hindrance the nucleophilic attack by the alcohol molecule on the protonated alcohol molecule does not occur. The protonated 2° and 3° alcohols lose water molecules to form stable 2° and 3° carbocations.
Question. Describe the following :
Unsymmetrical ether
Answer. Unsymmetrical ether : Ethers in which two alkyl groups are different are known as unsymmetrical ether. e.g., CH3OCH2CH3 Methoxyethane.
Short Answer Questions
Question. Write the main product(s) in each of the following reactions :
Answer.
Question. Write the final product(s) in each of the following reactions :
Answer.
Question. Name the reagents used in the following reactions :
(i) Bromination of phenol to 2, 4, 6-tribromophenol
(ii) Butan-2-one to Butan-2-o1
(iii) Friedel–Cra s alkylation of anisole
(iv) Oxidation of primary alcohol to carboxylic acid
Answer. (i) Bromine water, (Br2(aq))
(ii) Lithium aluminium hydride, (LiAlH4) or H2/Ni
(iii) Alkyl halide in the presence of anhydrours aluminium chloride, CH3Cl and AlCl3 (anhy.)
(iv) Acidified potassium permangante, KMnO4, H3O+
Question. How will you convert the following :
(i) Propan-2-ol to propanone.
(ii) Phenol to 2,4,6-tribromophenol.
Answer.
Question. Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.
Answer.
Question. How is 1-propoxypropane synthesised from propan-1-ol?
Answer. Propan-1-ol on treatment with conc. H2SO4 at 413 K would yield 1-propoxypropane. In this method, the alcohol is continuously added to keep its concentration in excess.
Question. Name the reagents and write the chemical equations for the preparation of the following compounds by Williamson’s synthesis :
(i) Ethoxybenzene
(ii) 2-Methyl-2-methoxypropane
Answer.
Long Answer Questions
Question. Classify the following as primary, secondary and tertiary alcohols :
Answer.
Question. Draw the structure and name of the product formed if the following alcohols are oxidized. Assume that an excess of oxidising agent is used.
(i) CH3CH2CH2CH2OH
(ii) 2-butenol
(iii) 2-methyl-1-propanol
Answer.
Question. Acid catalysed dehydration of t-butanol is faster than that of n-butanol. Explain.
Answer. Acid catalysed dehydration of alcohols follows carbocation mechanism.
Hence, dehydration of t-butanol which form 3° carbocation is faster than n-butanol which form primary carbocation.
