Class 12 Chemistry Sample Paper Set C

Please refer to Class 12 Chemistry Sample Paper Set C with solutions below. The following CBSE Sample Paper for Class 12 Chemistry has been prepared as per the latest pattern and examination guidelines issued by CBSE. By practicing the Chemistry Sample Paper for Class 12 students will be able to improve their understanding of the subject and get more marks.

Topic-1
Methods of Preparation and Properties of Alcohols and Phenols

Very Short Answer-Objective Type Questions

A. Multiple choice Questions:

Question. How many alcohols with molecular formula C₄H₁₀O are chiral in nature?
(a) 1
(b) 2
(c) 3
(d) 4

Question. The process of converting alkyl halides into alcohols involves_____________.
(a) addition reactiona(b) substitution reaction
(c) dehydrohalogenation reaction
(d) rearrangement reaction

Question. IUPAC name of m-cresol is ___________.
(a) 3-methylphenol
(b) 3-chlorophenol
(c) 3-methoxyphenol
(d) benzene-1,3-diol

Question. What is the correct order of reactivity of alcohols in the following reaction?

(a) 1° > 2° > 3°
(b) 1° < 2° > 3°
(c) 3° > 2° > 1°
(d) 3° > 1° > 2°

Question. Which of the following compounds will react with sodium hydroxide solution in water?
(a) C₆H₅OH
(b)C₆H₅CH₂OH
(c) (CH₃)₃COH
(d) C₂H₅OH

Question. Phenol is less acidic than ______________.
(a) ethanol
(b) o-nitrophenol
(c) o-methylphenol
(d) o-methoxyphenol

Question. Match the species given in Column I with those mentioned in Column II.

Answer. (i)—(e), (ii)—(f), (iii)—(d), (iv)—(c), (v)—(a),(vi)—(b)

C. Answer the following:

Question. Write the IUPAC name of the given compound :

Answer. 2, 5 – dinitrophenol 

Question. Write the IUPAC name of the given compound :

Answer. 2-Phenylethanol.

Question. Write the IUPAC name of the following :

Answer. 3-Bromo-3-methyl but-2-en-1-ol. 

Question. Write the IUPAC name of the following :

Answer. 2-methyl-propan-2-ol. 

Question. Write the IUPAC name of the following compound :

Answer. 2-Bromo-3-methylbut-2-en-1-ol. 

Question. Write the IUPAC name of the following compound:

Answer. 3 — phenyl-prop-2-en-1-o

Question. Write the IUPAC name of the following compound : C₆H₅–CH₂–CH₂–OH
Answer. 2-Phenylethanol. 

Question. Write the IUPAC name of the following compound :

Answer. 2 – Methylbut-3-en-2-ol

Question. Write the IUPAC name of the following compound :

Answer. 2 – Phenylpropan-2-ol 

Question. Draw the structural formula of 2-methyl propan-2- ol molecule.
Answer. 2-Methylpropan-2-ol

Question. Write the IUPAC name of the following:

Answer. 3,3 – Dimethylpentan-2-ol 

Question. Draw the structure of hex-1-en-3-ol compound.
Answer.

Question. Which of the following isomers is more volatile : o-nitrophenol or p-nitrophenol ?
Answer. o-nitrophenol. 

Question. Write the chemical reaction to explain Kolbe’s reaction.
Answer.

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 aliphatic while R′ is aromatic. 

Question. Give a chemical test to distinguish between 2-Pentanol and 3-Pentanol.
Answer. 3-pentanol immediately gives turbidity with Lucas reagent but 2-pentanol gives turbidity in around five minutes.

Question. How would you obtain ethane-1,2-diol from ethanol ?
Answer. 

Question. How would you obtain phenol from benzene ? 
Answer. 

Question. ortho-nitrophenol has lower boiling point than p-nitrophenol. Why ?
Answer. p-nitrophenol shows intermolecular hydrogen bonding. So it has higher boiling point. Whereas o-nitrophenol shows intramolecular H-bonding hence lower boiling point. 

Question. The C—O bond is much shorter in phenol than in ethanol. Give reason. 
Answer. Because in phenol, conjugation of unshared electron pair over oxygen with aromatic ring results in partial double bond character in carbon-oxygen bond.
In phenol, oxygen is attached to sp² hybridised carbon atom while in methanol it is attached to sp³ hybridised carbon atom. The bond formed between oxygen and sp² hybridised carbon is more stable i.e., shorter than that formed between oxygen and sp3 hybridised carbon. 

Question. Out of CH₃OH and

which one is more acidic ?
Answer. 

as phenoxide ion is more stable due to resonance which is absent in alkoxide ion. 

Question. What happens when phenol is oxidized by Na₂Cr₂O₇ / H₂SO₄?
Answer. 

Benzoquinone is formed.

Question. What happens when phenol is heated with zinc dust? 
Answer. 

Question. What happens when phenol is treated with bromine water?
Answer. 

Short Answer Type Questions  

Question. (i) Predict the major product of acid catalysed dehydration of 1-Methylcyclohexanol.
(ii) You are given benzene, conc. H₂SO₄, NaOH and dil.HCl. Write the preparation of phenol using these reagents.
OR
Draw the structures of any two isomeric alcohols (other than 1° alcohols) having molecular formula C₅H₁₂O and give their IUPAC names.
Answer. (i) 1-Methylcyclohexene

OR
Any two isomers out of the following :
(i) CH₃—CH₂—CH₂—CH(OH)—CH₃ Pentan-2-ol
(ii) CH₃—CH₂—CH(OH)—CH₂—CH₃ Pentan-3-ol 
(iii) CH₃—CH(CH₃)CH(OH)—CH₃ 3-Methybutan-2-ol
(iv) CH₃—CH₂—C(CH₃)(OH)—CH₃ 2-Methylbutan-2-ol 

Question. Write the equations involved in the following reactions :
(i) Reimer-Tiemann reaction
(ii) Williamson synthesis
Answer. (i) Reimer – Tiemann reaction

Question. Write the mechanism of acid dehydration of ethanol to yield ethene.
Answer. 

Question. (i) Write the mechanism of the following reaction :

(ii) Write the equation involved in Reimer-Tiemann reaction. 
Answer. 

Question. (i) Give chemical tests to distinguish between the following pairs of compounds : Methanol and Phenol
(ii) o-nitro phenol is more acidic than o-methoxy phenol.Explain why.
Answer. (i) Phenol gives a violet colouration with FeCl₃ solution while methanol does not. 
(ii) The electron withdrawing groups like –NO₂ increase the stability of phenoxide ion by dispersal of negative charge. The electron releasing groups like –OCH₃ decrease the acidic strength of phenol by destabilising the phenoxide ion by concentrating negative charge. Thus, o-nitrophenol is more acidic than o-methoxy phenol.

Question. Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.
Answer. 

Question. (i) Describe the mechanism of acid dehydration of ethanol to yield ethene.
(ii) Describe a chemical test to distinguish between ethanol and phenol.
Answer. (i) Acid dehydration of ethanol to ethene : When ethanol is heated with concentrated sulphuric acid at 453K, it undergoes dehydration and ethene is formed

Question. Write the mechanism of the following reaction :

Answer. 

Question. Explain the following behaviours :
(i) Alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.
(ii) ortho-nitrophenol is more acidic than orthomethoxyphenol.
Answer. (i) Alcohols are more soluble in water than the hydrocarbons of comparable molecular masses because alcohols form hydrogen bonds with water. 
(ii) The electron withdrawing groups like –NO₂ increase the stability of phenoxide ion by dispersal of negative charge. The electron releasing groups like –OCH₃ decrease the acidic strength of phenol by destabilising the phenoxide ion by concentrating negative charge. Thus, o-nitrophenol is more acidic then o-methoxyphenol. 

Question. (i) Arrange the following compounds in the increasing order of their acid strength: p-cresol, p-nitrophenol, phenol
(ii) Write the mechanism (using curved arrow notation) of the following reaction;
CH₂ = CH₂+ H₃O⁺ → CH₃ – CH₂⁺ + H₂O 
OR
Write the structures of the products when Butan-2-ol reacts with the following
(i) CrO₃
(ii) SOCl₂
Answer. 

OR

Long Answer Type Questions-I

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. How are the following conversions carried out ?
(i) Propene to propane-2-ol
(ii) Benzyl chloride to Benzyl alcohol
(iii) Anisole to p-Bromoanisole
Answer.

Question. How are the following conversions carried out ?
(i) Benzyl chloride to Benzyl alcohol
(ii) Ethyl magnesium chloride to Propan-1-ol
(iii) Propene to Propan-2-ol 
Answer. 

Question. Write the major products in the following

Answer.

Question. How do you convert the following :
(i) Phenol to anisole
(ii) Propan-2-ol to 2-methylpropan-2-ol
(iii) Aniline to phenol
OR
(i) Write the mechanism of the following reaction :

(ii) Write the equations involved in the acetylation of Salicylic acid. 
Answer.

Question. Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of oxidizing agent is used.
(i) CH₃CH₂CH₂CH₂OH
(ii) 2-butanol
(iii) 2-methyl-1-propanol 
Answer. (i) CH₃CH₂CH₂COOH
         Butanoic acid 
(ii) CH₃—CH=CH—COOH
But-2-en-1-oic acid or 2-butenoic acid 
(iii) CH₃—CH(CH₃)—COOH
2-methyl propanoic acid 

Question. (i) Give mechanism of preparation of ethoxy ethane from ethanol.
(ii) How is toluene obtained from phenol ? 
Answer.

Question. What happens when
(i) (CH₃)₃C– OH is treated with Cu at 573 K,
(ii) Anisole is treated with CH₃Cl/anhydrous AlCl₃,
(iii) Phenol is treated with Zn dust?
Write chemical equation in support of your answer. 
Answer. (i) (CH₃)₃ C-OH undergoes dehydration.

(ii) Methyl group is introduced at ortho and para positions.

Question. (i) Why phenol is more acidic than ethanol?
(ii) Write the mechanism of acid dehydration of ethanol to yield ether :

Answer. (i) Due to resonance, phenoxide ion is more stable than phenol whereas there is no resonance is alkoxide ion / explained with the help of resonating structures

Question. (i) Write Reimer-Temann reaction.
(ii) Write the mechanism of acid dehydration of ethanol to yield ethene:

Answer.

Question. (i) Complete the following reaction and suggest a suitable mechanism for the reaction :

(ii) Why ortho-Nitrophenol is steam volatile while para-Nitrophenol is less volatile?
Answer.

(ii) o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding.

Question. Explain the following behaviours:
(i) Alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.
(ii) Ortho-nitrophenol is more acidic than orthomethoxyphenol.
(iii) Cumene is a better starting material for the preparation of phenol.
Answer. (i) Because of H-bond formation between alcohol and water molecule.
(ii) Nitro being the electron withdrawing group stabilises the phenoxide ion.
(iii) Side product formed in this reaction is acetone which is another important organic compound.

Long Answer Type Questions-II

Question. (i) Write the formula of reagents used in the following reactions:
(a) Bromination of phenol to 2,4,6-tribromophenol
(b) Hydroboration of propene and then oxidation to propanol.
(ii) Arrange the following compound groups in the increasing order of their property indicated:
(a) p-nitrophenol, ethanol, phenol (acidic character)
(b) Propanol, Propane, Propanal (boiling point)
(iii) Write the mechanism (using curved arrow notation) of the following reaction:

Answer. (i) (a) Aq. Br₂ 
(b) B₂H₆, H₂O₂ and OH^– 
(ii) (a) ethanol<phenol<p-nitrophenol 
(b) propane <propanal<propanol

Question. Explain a process in which a biocatalyst is used in industrial preparation of a compound known to you. 
Answer. Biocatalysts are complex organic compounds which act as catalysts in reaction taking place in living organism. These biocatalysts (enzymes) are used in the manufacture of ethanol.
Ethanol from sugar solution (molasses):
Molasses is a non-crystalline form of sugar obtained as the mother liquor after crystallization of sugar from sugar solution. This contains about 50% sugar. It is diluted to about 10% solution and yeast is added and kept for about 2-3 days. Yeast supplies the enzymes invertase and zymase. The enzyme invertase hydrolyses sucrose to glucose and fructose to ethanol.

In wine making, grapes are the source of sugar and yeast. As grapes ripen, the quantity of sugar increases and the yeast grows on the skin of the grapes. When the grapes are crushed, sugar and enzyme come in contact and fermentation starts. Fermentation takes place under anaerobic conditions (i.e. in the absence of air). During fermentation, CO₂ is released.
The action of enzyme is inhibited when the concentration of alcohol exceeds 14%. If air enters the fermentation mixture, the O₂ released from the air oxidizes ethanol to ethanoic acid which spoils the taste of alcoholic drinks and make it sour.

Topic-2
Methods of Preparation and Properties of Ethers

Very Short Answer-Objective Type Questions

A. Multiple choice Questions:

Question. IUPAC name of the compound.

is ___________.
(a) 1-methoxy-1-methylethane
(b) 2-methoxy-2-methylethane
(c) 2-methoxypropane
(d) isopropylmethyl ether

Question. Which of the following species can act as the strongest base?
(a) – OH
(b) – OR
(c) – OC₆H₅

B. Answer the following:

Question. Write the IUPAC name of the given compound :

Answer. 1-Ethoxy-2-methylpropane. 

Question. Write the IUPAC name of the following compound:

Answer. 2-Methoxy -2- methylpropane 

Question. Write the equation involved in the reaction Williamson’s ether synthesis. 
Answer. 

Question. How would you obtain acetophenone from phenol ? 
Answer.

Question. An alkoxide is a stronger base than hydroxide ion. Justify. 
Answer. Due to the presence of an alkyl group, higher electron density is found in alkoxide ion. 

Short Answer Type Questions 

Question. Explain why is O=C=O nonpolar while R–O–R is polar. 
Answer. CO₂ is a linear molecule. The dipole moment of two C = O bonds are equal and opposite. Hence, they cancel each other. So, the dipole moment of CO₂ is
zero and it is a non-polar molecule.

While for ethers, two dipoles are pointing in the same direction. These two dipoles do not cancel the effect of each other. Therefore, there is a finite resultant dipole and hence, R—O—R is a polar molecule. 

Question. Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.
Answer. The formation of ethers by dehydration of alcohol is a bimolecular reaction (S_N2) involving the attack of an alcohol molecule on a protonated alcohol molecule. In the method, the alkyl group should be unhindered. In case of secondary or tertiary alcohols, the alkyl group is hindered. As a result, elimination dominates substitution. Hence, in place of ethers, alkenes are formed.

Long Answer Type Questions-I

Question.1. Explain the following with an example in each :
(i) Kolbe’s reaction (ii) Reimer-Tiemann reaction
(iii) Williamson ether synthesis 
Answer. (i) Kolbe’s reaction : Sodium phenoxide is heated with CO₂ at 400 K under a pressure of 4-7 atm which on acidification results in salicylic acid

(ii) Reimer-Tiemann reaction :

(iii) Williamson ether synthesis : An alkyl halide reacts with sodium alkoxide or sodium phenoxide to form ether

Question. State the products of the following reactions :
(i) CH₃CH₂CH₂OCH₃ + HBr →

Answer. (i) CH₃CH₂CH₂OCH₃ + HBr → CH₃CH₂CH₂OH + CH₃Br

Question. Write the structures of the main products in the following reactions:

Answer.

(ii) C₆H₅CH(OH)CH₃
(iii) C₂H₅I + C₆H₅OH

Question. The following is not an appropriate reaction for the preparation of tert-butyl ethyl ether.
C₂H₅ONa + (CH₃)₃C—Cl→(CH₃)₃C—OC₂H₅
(i) What would be the major product of the given reaction ?
(ii) Write a suitable reaction for the preparation of tertbutyl ethyl ether, specifying the names of reagents used. Justify your answer in both cases.
Answer. (i) Since the alkyl halide is a 3° halide and C₂H₅ONa is a strong base, therefore elimination occurs preferably. The product obtained is 2-Methylprop-1-ene. [CH₃—C(CH₃)=CH₂]. 
(ii) To prepare t-Butyl ethyl ether, the alkyl halide should be 1° i.e., chloroethane and the nucleophile should be sodium t-butoxide because the 3° nucleophile is able to attack 1° alkyl halide.
(CH₃)₃C—O–Na+ + CH₃CH₂— Cl→ (CH₃)₃COCH₂ CH₃

Question. Given reasons of the following :
(i) Phenol is more acidic than methanol.
(ii) The C–O–H bond angle in alcohols slightly less than the tetrahedral angle (109°28’).
(iii) (CH₃)₃C–O–CH₃ on reaction with HI gives
(CH₃)₃C–I and CH₃–OH as the main products and not (CH₃)₃C–OH and CH₃–I. 
Answer. (i) Phenol is more acidic than methanol as the phenoxide ion formed after removal of a proton is stabilised by resonance whereas the methoxide ion formed after removal from methanol is not. 
(ii) Due to lone pair-lone pair repulsion on oxygen atoms. 
(iii) The reaction between (CH₃)C—O—CH₃ and HI follows S_N1 mechanism. For an S_N1 reaction, the
formation of product is decided by the stability of the cabocation formed in the slowest step. As tertbutyl carbonium ion [(CH₃)₃C⁺] formed after the cleavage of C—O bond in the slowest step is more stable than methyl carbonium ion therefore (CH₃)₃ C-I and CH₃OH are formed as main products.