CBSE Class 12 Chemistry Halo Alkanes and Halo arenes Questions

Read and download free pdf of CBSE Class 12 Chemistry Halo Alkanes and Halo arenes Questions. Get printable school Assignments for Class 12 Chemistry. Class 12 students should practise questions and answers given here for Unit 10 Haloalkanes And Haloarenes Chemistry in Class 12 which will help them to strengthen their understanding of all important topics. Students should also download free pdf of Printable Worksheets for Class 12 Chemistry prepared as per the latest books and syllabus issued by NCERT, CBSE, KVS and do problems daily to score better marks in tests and examinations

Assignment for Class 12 Chemistry Unit 10 Haloalkanes And Haloarenes

Class 12 Chemistry students should refer to the following printable assignment in Pdf for Unit 10 Haloalkanes And Haloarenes in Class 12. This test paper with questions and answers for Class 12 Chemistry will be very useful for exams and help you to score good marks

Unit 10 Haloalkanes And Haloarenes Class 12 Chemistry Assignment

SHORT ANSWER TYPE QUESTIONS

Question. Haloalkanes react with KCN to form alkyl cyanides as main product while AgCN forms isocyanides as the chief product. Explain.
Answer. KCN is predominantly ionic and provides cyanide ions in solution. Both carbon and nitrogen atoms are in a position to donate electron pairs. The attack takes place mainly through carbon atom since C—C bond is more stable than C—N bond.
However, AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanides as the main product.

Question. Grignard reagents should be prepared under anhydrous conditions. Why?
Answer. Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons.
RMgX + H2O → RH + Mg(OH)X It is therefore necessary to avoid even traces of moisture from a Grignard reagent

Question. What are chiral and achiral molecules
Answer. The objects which are non- superimposable on their mirror image are said to be chiral and this property is known as chirality.
The objects, which are, superimposable on their mirror images are called achiral

Question. What do you mean by racemic mixture and racemization?
Answer. A mixture containing two enantiomers in equal proportions is known as racemic mixture.
It will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer.
The process of conversion of enantiomers into a racemic mixture is known as racemisation

Question. Cl is an electron withdrawing group but it is ortho, para- directing in electrophilic aromatic substitution reactions. Why?
Answer. • Chlorine withdraws electrons through inductive effect and releases electrons through resonance.
• Through inductive effect, chlorine destabilizes the intermediate carbocation and through resonance, halogen tends to stabilize the carbocation and the effect is more pronounced at ortho- and para- positions.
• The resonance effect tends to oppose the inductive effect for the attack at ortho- and para- positions and hence makes the deactivation less for ortho- and para- attack.
• Reactivity is thus controlled by the stronger inductive effect and orientation is controlled by resonance effect.


CASE BASED QUESTIONS

Read the following passage and answer the questions given below.

SN1 reactions are generally carried out in presence of protic solvents. Like acetic acid. The reaction between a tertiary alkyl halide and nucleophile follows the first order kinetics. The rate of reaction depends on the concentration of alkyl halide .it occurs in two steps. In first step step C-X bond undergoes cleavage to form carbocation, it is then attacked by nucleophile in second step which is very fast. The energy needed for breaking C-X bond is obtained through solvation of halide ion with proton of protic solvent. Greater the stability of carbocation, Greater will be its ease of formation and faster will be its rate of reaction. In the case of optically active alkyl halide SN1 reaction is accompanied by Racemisation. The carbocation formed in step one is sp2 hybridised. Which is triagonal planar. The attack of nucleophile may be accomplished from either side to give a mixture of products.

Question. Assertion: SN2 reaction takes place in presence of protic solvent.
Reason: The energy is released by the solvation of halide ion with proton.
Answer. D

Question. Assertion. The rate of SN1 reaction depends only on the concentration of alkyl halide.
Reason: Formation of carbocation is slow step and slow step determines the rate of reaction.
Answer. A

Question. Assertion: Tertiary alkyl halides reacts faster in SN1 reaction
Reason. Tertiary carbocations are more stable and formed at faster rate.
Answer. A

Question. Assertion: During SN1 reaction of an optically active alkyl halide Racemisation takes place
Reason. Racemic mixture consists of equal amount of dextro and leavo isomer.
Answer. B

Question. Assertion: Attack of nucleophile to carbon of carbocation takes place through either side forming two isomers with opposite configuration.
Reason: Carbocation is sp3 hybridised and have triogonal planar geometry
Answer. C

Question. Assertion: - In SN1 reaction second step is very fast and reversible.
Reason: - The carbocation formed is highly unstable and highly reactive.
Answer. D

 

OR
Read the passage given below and answer the following questions: Nucleophilic substitution reactions are of two types; substitution nucleophilic bimolecular (SN2) and substitution nucleophilic unimolecular (SN1) depending on molecules taking part in determining the rate of reaction. Reactivity of alkyl halide towards SN1 and SN2 reactions depends on various factors such as steric hindrance, stability of intermediate or transition state and polarity of solvent. SNreaction mechanism is favoured mostly by primary alkyl halide then secondary and then tertiary. This order is reversed in case of SN1 reactions.
The following questions are multiple choice questions. Choose the most appropriate Answer.

Question. Which of the following is most reactive towards nucleophilic substitution reaction?
(a) C6H5Cl
(b) CH2=CHCl
(c) ClCH2CH=CH2
(d) CH3CH=CHCl
Answer. C

Question. Isopropyl chloride undergoes hydrolysis by
(a) SNmechanism
(b) SN2mechanism
(c) SN1 and SN2mechanism
(d) neither SN1 and SNmechanism
Answer. C

Question. The most reactive nucleophile among the following is
(a) CH3O-
(b) C6H5O-
(c) (CH3)2CHO-
(d) (CH3)3CO-
Answer. A

Question. Tertiary alkyl halides are practically inert to substitution by SN2mechanism because of
(a) insolubility
(b) instability
(c) inductive effect
(d) stearic hindrance.
Answer. D

Question. Account for the following :
(a) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
(b) Alkyl halides, though polar, are immiscible with water.
(c) Grignard’s reagents should be prepared under anhydrous conditions.
Answer. (a) Electron pairs of Cl atom are in conjugation with n electrons of the benzene ring so C-Cl bond in chlorobenzene acquires some double bond character while C-Cl bond in cyclohexyl chloride is a pure single bond. C – Cl bond in chlorobenzene is shorter than in cyclohexyl chloride. Since dipole moment is a product of charge and distance, so chlorobenzene has lower dipole moment than cyclohexyl chloride.
(b) Alkyl halides are polar molecules, therefore, their molecules are held together by dipole-dipole attraction. The molecules of H2O are held together by H-bonds. Since the new forces of attraction between water and alkyl halide molecules are weaker than the forces of attraction already existing between alkyl halide- alkyl halide molecules and water- water molecules, therefore, alkyl halides are immiscible with water.
(c) Grignard’s reagents are very reactive. They react with alcohol, water, amines etc. to form corresponding hydrocarbon. R-MgX + HOH → RH + Mg(OH)X Therefore, Grignard’s reagents must be prepared under anhydrous conditions

Question. Give reasons : (a) n-Butyl bromide has higher boiling point than f-butyl bromide
(b) Racemic mixture is optically inactive.
(c) The presence of nitro group (-NO2) at o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.
Answer.
(a) n-Butyl bromide has higher boiling point than f-butyl bromide because it has larger surface area hence have more Van der Waals’ forces.
(b) Rotation due to one enantiomer is cancelled by another enantiomer.
(c) The presence of nitro group (-NO2) at ortho and para positions withdraws the electron density’ from benzene ring and thus facilitating the attack of nucleophile.

Question. a) Account for the following : (i) Electrophilic substitution reactions in haloarenes occur slowly.
(ii) Haloalkanes, though polar, are insoluble in water.
(b) Arrange the following compounds in increasing order of reactivity towards SN2 displacement: 2-Bromo-2-Methylbutane, 1-Bromopentane, 2-Bromopentane 
Answer. (a) (i) Due to -I effect of halogen atom, it withdraws electrons from the benzene ring and thus ring gets deactivated.
(ii) They fail to form hydrogen bonds with water. More energy is required to break hydrogen bonds in water and less energy is released when new attractions are set up.
(b) 2-Bromo-2-Methylbutane < 2-Bromopentane < 1-Bromopentane

 

CBSE Class 12 Chemistry Halo Alkanes and Halo arenes Questions

(ix) (CCl3)3 CCl
2. Write the structure of following halogen compounds
(i) 2-chloro-3-methylpentane
(ii) 2-(2-chlorophenyl)-1-iodooctane
(iii) 1-bromo-4-sec-butyl-2–methylebenzene.
(iv) p-bromotoluene.
(v) chlorophenylmethane

3. Arrange the following in the increasing order of properly indicated :
(i) bromomethane, chloromethane, dichloromethane. (Increasing order of boiling points).
(ii) 1-chloropropane, isopropyl chloride, 1-chlorobutane (Increasing order of boiling point)
(iii) dichloromethane, chloroform, carbon terachloride. (Increasing order of dipole moment.
(iv) CH3F, CH3Cl, CH3Br, CH3l (Increasing reactivity towards nucleophilic substitution and increasing order of dipole moment)
(v) o,m.p-dichlorobenzenes (Increasing order of melting points).

4. Complete the following reactions

 CBSE Class 12 Chemistry - Halo Alkanes and Halo arenes Questions

Please refer to the link below for CBSE Class 12 Chemistry Halo Alkanes and Halo arenes Questions

Unit 12 Aldehydes, Ketones and Carboxylic Acids
CBSE Class 12 Chemistry Aldehydes Ketons Carboxylic Acids Questions

More Study Material

CBSE Class 12 Chemistry Unit 10 Haloalkanes And Haloarenes Assignment

We hope you liked the above assignment for Unit 10 Haloalkanes And Haloarenes which has been designed as per the latest syllabus for Class 12 Chemistry released by CBSE. Students of Class 12 should download and practice the above Assignments for Class 12 Chemistry regularly. We have provided all types of questions like MCQs, short answer questions, objective questions and long answer questions in the Class 12 Chemistry practice sheet in Pdf. All questions have been designed for Chemistry by looking into the pattern of problems asked in previous year examinations. 

Assignment for Chemistry CBSE Class 12 Unit 10 Haloalkanes And Haloarenes

Our team of expert teachers have referred to NCERT book for Class 12 Chemistry to design the Chemistry Class 12 Assignments. If you practice at least one test paper daily, you will get higher marks in Class 12 exams this year. Daily practice of Chemistry course notes and related study material will help you to clear all your doubts and have stronger understanding of all concepts. You can download all Revision notes for Class 12 Chemistry also from www.studiestoday.com absolutely free of cost.

Unit 10 Haloalkanes And Haloarenes Assignment Chemistry CBSE Class 12

All questions and their answers for the assignment given above for Class 12 Chemistry have been developed as per the latest curriculum and books issued for the current academic year. The students of Class 12 can rest assured that the best teachers have designed the questions of Chemistry so that you are able to revise the entire syllabus if you do the assignments. Lot of MCQ questions for Class 12 Chemistry have also been given in the worksheets and assignments for regular use. All study material for Class 12 Chemistry students have been given on studiestoday.

Unit 10 Haloalkanes And Haloarenes Assignment CBSE Class 12 Chemistry

Regular assignment practice helps to get a more comprehensive understanding of Unit 10 Haloalkanes And Haloarenes concepts. Assignments play a crucial role in understanding Unit 10 Haloalkanes And Haloarenes in CBSE Class 12. Students can download all the assignments of the same chapter in Class 12 Chemistry in Pdf format. You can print them or read them online on your computer or mobile.

CBSE Chemistry Class 12 Unit 10 Haloalkanes And Haloarenes Assignment

CBSE Class 12 Chemistry latest books have been used for coming up with the latest questions and solutions for the above assignment. If you have revised all concepts relating to Unit 10 Haloalkanes And Haloarenes then you should attempt all questions given in the test sheets above. We have also provided lot of Worksheets for Class 12 Chemistry which you can use to further make your self stronger in Chemistry

Where can I download in PDF assignments for CBSE Class 12 Chemistry Unit 10 Haloalkanes And Haloarenes

You can download free Pdf assignments for CBSE Class 12 Chemistry Unit 10 Haloalkanes And Haloarenes from StudiesToday.com

The assignments for Unit 10 Haloalkanes And Haloarenes Class 12 Chemistry for have been made based on which syllabus

The Unit 10 Haloalkanes And Haloarenes Class 12 Chemistry Assignments have been designed based on latest CBSE syllabus for Class 12 Chemistry issued for the current academic year

Can I download and print these printable assignments for Chemistry Unit 10 Haloalkanes And Haloarenes Class 12

Yes, These printable assignments for Unit 10 Haloalkanes And Haloarenes Class 12 Chemistry are free to download and print

How many topics are covered in Unit 10 Haloalkanes And Haloarenes Chemistry assignments for Class 12

All topics given in Unit 10 Haloalkanes And Haloarenes Chemistry Class 12 Book for the current academic year have been covered in the given assignment

Is there any charge for this assignment for Unit 10 Haloalkanes And Haloarenes Chemistry Class 12

No, all Printable Assignments for Unit 10 Haloalkanes And Haloarenes Class 12 Chemistry have been given for free and can be downloaded in Pdf format

How can I download the printable test assignments for Unit 10 Haloalkanes And Haloarenes Chemistry Class 12

Just click on the View or Download button below, then another window with the Pdf will be visible, just click on the Pdf icon to download the free assignments for Unit 10 Haloalkanes And Haloarenes Class 12 Chemistry

Are these assignments available for all chapters in Class 12 Chemistry

Yes, apart from Chemistry you can download free assignments for all subjects in Class 12

Can I download solved assignments for Unit 10 Haloalkanes And Haloarenes CBSE Class 12 Chemistry

Our team of expert teachers at studiestoday.com have provided all answers for the practice questions which have been given in Class 12 Chemistry Unit 10 Haloalkanes And Haloarenes assignments