For all Agricultural, Medical, Pharmacy and Engineering Entrance Examinations held across India.

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1 For all Agricultural, Medical, Pharmacy and Engineering Entrance Examinations held across India. Absolute NEET UG & JEE (Main) CHEMISTRY Vol. 1. Salient Features Precise theory for every topic. Exhaustive subtopic wise coverage of MCQs. 011 MCQs including questions from various competitive exams. Includes MCQs from AIPMT & Re-Test 015, NEET P-I & P-II 016, JEE (Main) 015 & 16. Relevant Hints provided. Quick Review and Additional Information to build concepts. Topic-wise test at the end of each chapter. Solutions/hints to Topic Test available in downloadable PDF format at Printed at: Jasmine Art Printers Pvt. Ltd., Navi Mumbai Target Publications Pvt. Ltd. No part of this book may be reproduced or transmitted in any form or by any means, C.D. ROM/Audio Video Cassettes or electronic, mechanical including photocopying; recording or by any information storage and retrieval system without permission in writing from the Publisher. 1110_110_JUP P.O. No

2 PREFACE Target s Absolute Chemistry Vol - 1. is compiled according to the notified Std. XI syllabus for NEET-UG & JEE (Main). The content of this book is framed after reviewing various state syllabi as well as the ones prepared by CBSE, NCERT and COBSE. The sections of Theory, Quick Review, Formulae, MCQs and Topic Test form the backbone of every chapter and ensure adequate revision. These MCQs are framed considering the importance given to every topic as per the NEET-UG & JEE (Main) exam. They are a healthy mix of theoretical, numerical, multi-step and graphical based questions. The level of difficulty of these questions is at par with that of various competitive examinations like CBSE, AIIMS, CPMT, JEE, AIEEE, TS EAMCET (Med. and Engg.), BCECE, Assam CEE, AP EAMCET (Med. and Engg.) & the likes. Also to keep students updated, questions from most recent examinations such as AIPMT/NEET, MHT CET, KCET, GUJ CET, WB JEEM, JEE (Main), of years 015 and 016 are exclusively covered. In the development of each chapter, we have ensured the inclusion of important points that are enclosed within a box. These topics will enhance students knowledge and provide them an edge to score better in the highly competitive exams. We are confident that this book will cater to needs of students across a varied background and effectively assist them to achieve their goal. We welcome readers comments and suggestions which will enable us to refine and enrich this book further. Please write to us at: mail@targetpublications.org All the best to all Aspirants! Yours faithfully, Authors Index No. Topic Name Page No. 8 Redox Reactions 1 9 Hydrogen s-block Elements (Alkali and Alkaline Earth Metals) Some p-block Elements Organic Chemistry - Some Basic Principles and Techniques Alkanes Alkenes Alkynes Aromatic Hydrocarbons Environmental Chemistry 419 'Chapters 1 to 7 are a part of Absolute Chemistry Vol - 1.1'

3 08 Redox Reactions Chapter 08: Redox Reactions 8.0 Introduction 8.1 Concept of oxidation and reduction 8. Redox (Oxidation reduction ) 8.3 Oxidation number 8.4 Change in oxidation number 8.5 Balancing redox in terms of loss and gain of electrons 8.0 Introduction Chemical reaction: A reaction in which two substances chemically react with each other to give products is called chemical reaction. Chemical Precipitation Oxidation-reduction or Redox Acid-base Neutralization Importance of redox : i. The redox are a very important group of which occur with almost every element. ii. These are involved in large number of processes in nature (biological and industrial). iii. They take place in burning of fuels such as gasoline, oil, natural gas, organic substances of carbon and hydrogen and so on. iv. The redox are involved in household bleaching. v. The metallic elements are extracted from their ores by oxidation-reduction. vi. The functioning of batteries is based on redox. vii. The corrosion of metals involve redox. 8.1 Concept of oxidation and reduction Oxidation: i. According to the classical concept, Oxidation is defined as the addition of oxygen or any other electronegative element or removal of hydrogen or any other electropositive element. ii. According to the modern concept, Oxidation is a process which involves loss of electrons. It is also called de-electronation. iii. Oxidation increases the oxidation number of the element in the given substance and it involves, a. Addition of oxygen. C + O CO b. Addition of an electronegative element. Zn + S ZnS c. Removal of hydrogen. H S + Br HBr + S d. Removal of an electropositive element/radical. KI + Cl KCl + I 1

4 Chemistry Vol 1. (Med. and Engg.) Reduction: i. According to the classical concept, Reduction is defined as the addition of hydrogen or any other electropositive element or removal of oxygen or any other electronegative element ii. According to the modern concept, Reduction is a process which involves gain of electrons. It is also called electronation. iii. Reduction decreases the oxidation number of the element in the given substance and it involves, a. Addition of hydrogen. Cl + H HCl b. Addition of an electropositive element. HgCl + SnCl Hg Cl + SnCl 4 c. Removal of oxygen. ZnO + C Zn + CO d. Removal of an electronegative element/ radical. FeCl 3 + H FeCl + HCl Oxidizing agent: i. The substance which gains one or more electrons (i.e.itself gets reduced) is called oxidizing agent or oxidant. ii. Oxidizing agent increases the oxidation number of an element in a given substance. Eg. O, Cl, Br, H O, HNO 3, CO, etc. Reducing agent: i. The substance which loses one or more electrons (i.e.,itself gets oxidized) is called reducing agent or reductant. ii. Reducing agent lowers the oxidation number of an element in a given substance. Eg. H, Fe, Cu, C, LiAIH 4, Sodium amalgam etc. 8. Redox (Oxidation reduction ) Redox : i. The in which both oxidation and reduction occur simultaneously (together) are called redox. ii. In these, one substance acts as a reducing agent and itself gets oxidized while another substance acts as an oxidizing agent and itself gets reduced. Eg. Reaction between zinc and copper (II) salt occuring in a battery. In this reaction, zinc loses electrons and gets oxidized, whereas Cu + ions gain electrons and get reduced. loss of e : Oxidation Zn (s) + Cu Zn + Cu (s) iii. iv. gain of e : Reduction In the direct redox reaction, the transferance of electrons is limited to very small distances and therefore, no useful electrical work could be obtained. In these, chemical energy appears as heat. If the transferance of electrons from zinc to copper ions is allowed to occur through some metallic wires, useful electrical work could be performed. Such redox are called Indirect redox and electrical energy is produced during such spontaneous instead of heat energy. v. In this case, zinc acts as a reducing agent or reductant, while Cu + ions act as an oxidizing agent or oxidant. Other examples of redox are, Zn + HCl ZnCl + H 5Fe + + 8H + + MnO 4 5Fe 3+ + Mn + + 4H O vi. Examples for substances which can act both as oxidising as well as reducing agents are SO, H O, HNO etc.

5 Chapter 08: Redox Reactions Half : Every redox reaction according to the electronic concept consists of two known as half-. These are: i. Oxidation half reaction (loss of electrons). ii. Reduction half reaction (gain of electrons). Eg. The reaction involving zinc and dilute HCl. The two half are: aq Zn (s) Zn + e aq H + e H (g) Zn (s) + H aq Zn aq + H (g) (oxidation half reaction) (reduction half reaction) (overall reaction) Types of redox : Redox Combination Decomposition Displacement Disproportionation Metal displacement Non-metal displacement i. Combination : a. The chemical in which two or more substances (elements or compounds) combine to form a single substance are called combination. b. A combination reaction may be expressed as, A + B C c. For combination reaction to be a redox reaction one or both A and B must be in the elementary form. Eg C (s) + O (g) CO ; (g) 3Mg (s) + N (g) Mg 3 N (s) ii. iii. Decomposition : a. The chemical in which a compound breaks up into two or more simple substances are called decomposition. b. The decomposition are the opposite of combination. c. A decomposition reaction is the breakdown of a compound into two or more compounds atleast one of which must be in the elemental state. Eg Δ H O (l) H (g) + O (g) ; Δ KClO 3(s) KCl (s) + 3O (g) Note: All decomposition are not redox. Eg. Decomposition of calcium carbonate is not a redox reaction Δ CaCO 3(s) CaO (s) + CO (g) Displacement : a. The in which one ion (or atom) in a compound is replaced by an ion (or atom) of other element are called displacement. b. Displacement may be expressed as: X + YZ XZ + Y 3

6 Chemistry Vol 1. (Med. and Engg.) iv. c. These are of two types: 1. Metal displacement: In these, a metal in a compound can be displaced by another metal in the uncombined state. Eg. V O 5(s) + 5Ca (s) V (s) + 5CaO (s). Non-metal displacement: The non-metal displacement redox include hydrogen displacement and a rarely occurring reaction involving oxygen displacement. i. All alkali metals and some alkaline earth metals (Ca, Sr and Ba) which are very good reductants, will displace hydrogen from cold water. Eg Na (s) + H O (l) NaOH + H (g) ii. Less active metals such as magnesium and iron react with steam to produce hydrogen gas. Eg Mg (s) + H O (l) Mg(OH) + H (g) iii. Many metals, including those which do not react with cold water, are capable of displacing hydrogen from acids. Eg Mg (s) + HCl MgCl + H (g) iv. Metals like cadmium and tin do not react with steam, but react with acids to displace hydrogen gas. Eg CuSO 4 + Zn (s) Cu (s) + ZnSO Cd (s) + HCl CdCl + H (g) Disproportionation : a. In a disproportionation reaction, an element in one oxidation state is simultaneously oxidized and reduced. b. Atleast one reacting substance in a disproportionation reaction always contains an element that has both higher and lower oxidation states existing for that element. Eg. The decomposition of hydrogen peroxide is an example of the reaction, where oxygen element experiences disproportionation. Reduced O (g) H O H O (l) Oxidized In this reaction, oxidation number of O decreases from 1 to (in H O) and increases from 1 to 0 (in O ). Note: 1. All redox are exothermic.. Phosphorus, sulphur and chlorine undergo disproportionation in the alkaline medium as shown below: Reduced 4 0 P 4(s) OH + 3H O (l) PH 3(g) + 3HPO Oxidized In this reaction, oxidation number of P increases from 0 to + 1 (in HPO ) and decreases from 0 to 3 (in PH 3 ).

7 Chapter 08: Redox Reactions 8.3 Oxidation number Oxidation number: i. The charge which an atom appears to have, when all other atoms are removed from it as ions is known as oxidation number. OR The oxidation number or oxidation state of an atom in a molecule or ion is defined as the number of charges it would carry if electrons were completely transferred. ii. Metals invariably have positive oxidation states, while non-metals may have positive or negative oxidation states. iii. Transition metals usually display several oxidation states. iv. The highest positive oxidation state for s-block elements is equal to its group number but for p-block elements it is equal to group number minus 10 (except for noble gases). v. However, the highest negative oxidation state for p-block elements is equal to eight minus (8 ) the number of electrons in the valence shell. Eg. In the third period, the highest positive oxidation state or number increases from + 1 to + 7 as shown below: Group Element Na Mg Al Si P S Cl Compounds NaCl MgSO 4 AlF 3 SiCl 4 IF 5, P 4 O 10 SF 6, SO 3 HClO 4, Cl O 7 Oxidation state of the underlined element in the compound Rules to assign oxidation number or oxidation states to an atom: i. If there is a covalent bond between, a. two same atoms then, oxidation number of both the atoms will be zero. Eg. In a chlorine molecule, the oxidation number of both the chlorine atoms is zero. b. two different atoms then, electrons are counted more towards electronegative atom and, 1. more electronegative atom will be negative.. less electronegative atom will be positive. Eg. In a HCl molecule, the oxidation number of chlorine (more electronegative atom) is 1 and that of hydrogen (lesser electronegative atom) is +1. ii. If there is a co - ordinate bond between two atoms then, a. Oxidation number of acceptor atom will be. b. Oxidation number of donor atom will be +. iii. The oxidation number of an element in the free or elementary state or in any of its allotropic forms is always zero. iv. Eg. Oxidation numbers of helium in He, hydrogen in H, Oxygen in O or O 3 are zero. The oxidation number of an element in a single (monoatomic) ion is same as the charge on the ion. Eg. Oxidation number of K + is + 1, and Ca + is +. v. In binary compounds of metals and non-metals the oxidation number of metals is always positive while that of non-metals is negative. Eg. In NaCl, the oxidation number of sodium is + 1 and that of chlorine is 1. vi. vii. In compounds formed by the combination of non-metallic atoms, the atom with higher electronegativity is given negative oxidation number. Eg. In HCl, the oxidation number of chlorine is 1 because of it s high electronegativity. In all compounds of hydrogen, the oxidation number of hydrogen is + 1 except in hydrides of active metals such as LiH, NaH, KH, MgH, etc., where hydrogen has the oxidation number of 1. 5

8 Chemistry Vol 1. (Med. and Engg.) viii. The oxidation number of oxygen is in most of the compounds. However, there are two exceptions. a. The first exception is peroxides and superoxides in which oxygen atoms are directly linked to each other. Eg. In peroxides i.e. H O, each oxygen atom is assigned an oxidation number of 1 and in superoxides i.e. KO, RbO etc. each oxygen atom is assigned an oxidation number of 1/. b. The second exception is found in compounds in which oxygen is bonded to fluorine. Eg. In OF (oxygen difluoride) the oxidation no. of O is + and in O F (dioxygen fluoride), the oxidation no. of each O is +1. ix. The most electronegative element, fluorine always has an oxidation number 1. For other halogens, the oxidation number is generally 1, but there are exceptions, when these are bonded to a more electronegative halogen atom or oxygen. Eg. In HI, the oxidation number of I is 1 but in IF 5, it is + 5 and in IF 7, it is + 7. x. For neutral molecule, the sum of the oxidation numbers of all the atoms is equal to zero. Eg. In NH 3, Nitrogen is in 3 oxidation state, whereas hydrogen is in + 1 oxidation state and there are three hydrogen atoms present. Therefore the net charge is zero i.e. 3 and + 3 equals to zero. 8.4 Change in oxidation number i. The oxidation number is more oftenly termed as oxidation state. ii. In an oxidation process, the oxidation number of the element increases in the given substance whereas in a reduction process, the oxidation number of the element decreases in the given substance. iii. Oxidising agent increases the oxidation number of an element in a given substance whereas Reducing agent lowers the oxidation number of an element in a given substance. iv. Redox involve the change in oxidation number of interacting species. Eg. The reaction between zinc and hydrochloric acid. The oxidation number of all the atoms are written above their respective symbols, Oxidized 0 Zn HCl + 1 ZnCl + 0 H Reduced In this reaction, the oxidation number (O. N.) of zinc increases from 0 to + and that of hydrogen decreases from + 1 to 0, while that of chlorine remains unchanged. Thus, zinc is oxidized while hydrogen is reduced. 8.5 Balancing redox in terms of loss and gain of electrons Methods for balancing redox Oxidation number method Ion-electron method (Half-reaction method) Oxidation number method: The oxidation number method for balancing the redox follows the basic principle that the total increase in oxidation number must be equal to total decrease in oxidation number. Steps involved in balancing of redox by the oxidation number method are given as follows: i. Write the unbalanced net equation for the redox reaction. Balance the equation for all atoms except H and O. 6

9 Chapter 08: Redox Reactions ii. Assign the oxidation numbers to all atoms in the reactants and the products, using the rules to assign oxidation number. Identify the atoms undergoing change in oxidation numbers. iii. Show an increase in oxidation number per atom of the oxidized species and hence, the net increase in oxidation number. Similarly, show a decrease in oxidation number per atom of the reduced species and the net decrease in oxidation number. iv. Determine the factor that will make the total increase and decrease in oxidation numbers equal. Insert these coefficients into the equation. v. Balance oxygen atoms by adding H O to the side containing less O atoms, one H O for one O atom. Balance H atoms by adding H + ions, to the side with less H atoms. vi. If the reaction occurs in basic medium, then add OH ions, equal to the number of H + on both sides of the equation. The H + and OH ions appearing on the same side of the reaction are combined to give H O molecules. vii. Check the balanced equation to make sure that the reaction is balanced with respect to both the number of atoms of each element and the charges. Note: For a reaction in alkaline medium all the steps are applicable. However, if the reaction occurs in acidic medium, point (vi) is omitted. a. Reaction occurring in acidic medium: 3+ H O + CrO 7 O (g) + Cr 1. Balance Cr atom and assign oxidation number to each atom. H O + Cr O 3+ O (g) Identify the atoms undergoing change in oxidation number. The oxidation number of Cr reduces from + 6 to + 3. i.e., undergoes reduction by gain of three electrons and is an oxidizing agent. The oxidation number of O increases from 1 to 0 by loss of two electrons. i.e., it acts as a reducing agent and itself gets oxidized. H O + CrO 7 O (g) + 3+ Cr Gain of e Loss of e 3. Find the total increase in oxidation number for the oxidized atom and total decrease in oxidation number for the reduced atom. i. Increase in oxidation number : O ( 1) O (0). Increase per atom = + 1 Net increase = +. ii. Decrease in oxidation number : Cr (+ 6) Cr (+ 3) Decrease per atom = 3 Net decrease = Choose the factors that will make net increase and decrease equal. The net increase must be multiplied by 3. Hence, the coefficient 3 is needed for the O species on both sides. 3H O + CrO O (g) + Cr 5. Balance the equation for O atoms by adding H O to the side with less O atoms. There are 13 (O) atoms on the left side and 6 (O) atoms on the right side. Hence, add 7 H O molecule to the right side. 3H O + Cr O 3+ 3O (g) + Cr + 7H O (l) 7 Cr 6. Balance the equation for H atoms by adding H + ions on the side with less H atoms. There are 6 (H) atoms on left side whereas 14 (H) atoms on right side. Hence add 8H + to the left side. 3H O + CrO H 3O (g) + Cr + 7H O (l) Thus, the equation is balanced for both charge as well as atoms. 7

Oxidation, Reduction, Red-ox reactions, Types

Oxidation, Reduction, Red-ox reactions, Types 1) Oxidation number is the charge which an atom appears to acquire in a molecule, when all the bonding electrons are counted to more electro negative element.