Since HCl is a very weak reducing agent, it can not reduce H2S04 to S02 and hence HCl is not oxidised to Cl2. (iii) In O3, the O.N. Thus, there is no fallacy about the O.N. Answer: In a disproportionation reaction an element in one oxidation state is simultaneously oxidised and reduced. (i) C in CH3COOH (ii) S in S2O8-2 However, for covalent compounds oxidation and reduction or redox reactio… (c) 2. Answer: Let the oxidation number of S in H2SO4 be x. Question 5. Since the oxidation potential of Ag is much higher than that of H2O, therefore, (d) 2K(s) +F2(g)——> 2K+F–(s) Question 10. Question 14. OX of sulphur bonded with coordinate bond = 5, Average oxidation number = 5 + 5 + 0 + 0 / 4 = 5 / 2, There are two types of nitrogen atoms. Writing electrode potential for each half reaction from Table 8.1, we have. F2(g) + 2I–(aq) ———-> 2F–(aq) + I2(s); Cl2 (g) + 2Br–(aq) ————> 2Cl–(aq) + Br2 (Z) This article provides the revision notes of the Redox Reactions chapter of Class 11 Chemistry for the students so that they can give a quick glance of the chapter. Answer: (a) Cl2, HCl, HOCl, HOClO, HOClO2, HOClO3 respectively. Which of these will actually get discharged would depend upon their electrode potentials which are given below: Suggest structure of these compounds. 4. (CN)2(g) + 2OH–(aq) —–> CN–(aq) + CNO–(aq) + H2O(l) Question 3. Question 6. Answer: It is based upon the relative positions of these metals in the activity series. Question 21. Two questions should be asked to determine if a reaction is a redox reaction: Question 12. Calculate the oxidation number of Cr in [Cr (H2O)6]3+ ion. (b) The purpose of writing O2 two times suggests that O2  is being obtained from each of the two reactants. The O.N. of S by chemical bonding method. Question 10. Since P undergoes decrease as well as increase in oxidation state thus it is an example of disproportionation reaction. Fluorine reacts with ice and results in the change: If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. (i) by 2 and add it to Eq. Therefore, CuO is reduced to Cu but H 2 is oxidised to H 2 0. But the amount of O2 which is actually available is 20.0 g which is less than the amount which is needed. Answer: The balanced equation for the reaction is: MnO2 (s) + 4HF(l) ———–> No reaction. However, if formed, the compound acts as a very strong oxidising agent. (b)Fe2+ +Cr2O72-+ H+ ——–> Fe3+ + Cr3++ H2O, Question 5. Answer: Oxidation involves increase in O.N while reduction involves decrease in O.N. Slide 6: You used a “which” clause in the wrong place. Redox reactions are balanced by … of Fe decreases from +3 if Fe 2 O 3 to 0 in Fe while that of C increases from +2 in CO to +4 in CO 2. P4 acts both as an oxidising as well as a reducing agent. Where there is oxidation, there is always reduction – Chemistry is essentially a study of redox systems. We use the reaction between copper and silver nitrate to show a displacement reaction. Thus, it is a redox reaction. K+/K = -2.93 V, Ag+/Ag = 0.80 V, Hg2+/Hg = 0.79 V, Mg2+/Mg = -2.37 V, Their electrode potentials are: of S cannot be more than six since it has only six electrons in the valence shell. Answer: EMF of a cell is the difference in the electrode potentials of the two electrodes in a cell when no current flows through the cell. The Mn3+ ion is unstable in solution and undergoes disproportionation to give Mn2+, MnO2 and H+ ion. (a) F (b) Br (c) I (d) Cl Therefore, we must consider its structure, K+[I —I <— I]–. CU2++ 2e– ———> Cu(s); E° = +0.34 V The oxidation number of atoms in their elemental state is taken as zero. (b) HCHO is oxidised, Ag+   is reduced.Ag+  is oxidising agent whereas HCHO is reducing agent. Question 11. (a) Formulate possible compounds of’Cl’ in its O.S. Why is standard hydrogen electrode called reversible electrode? of Cu decreases from + 2 in CuO to 0 in Cu but that of H increases from 0 in H2 to +1 in H20. Tro - Chapter 16 2 Oxidation-Reduction Reactions • oxidation-reduction reactions are also called redox reactions • all redox reactions involve the transfer of electrons from one atom to another • spontaneous redox reactions are generally exothermic, and we can use their released energy as a source of energy for other applications Answer: Question 14. (a) HNO3 acts only as an oxidising agent while HNO3 can act both as reducing and oxidising agent.  Answer: The average O.N. and hence it acts as an oxidant only. To do so, Eq. Answer:Â. Chemical reactions which involves both oxidation as well as reduction process simultaneously, are known as redox reactions (‘red’) from reduction and ‘ox’ from oxidation). Revision Video. Redox reaction can be balanced through (i) Ion electron method (ii) Oxidation number method. (a) Calculate the oxidation number of (I) sulphate, (e) Iron (III) sulphate, (f) Chromium (III) oxide. Justify-giving reactions that among halogens, fluorine is the best oxidant and among hydrohalic compounds, hydroiodic add is the best reductant. Since the electrode potential of CU2+(aq) ions is much higher than that of H2O, therefore, at the cathode, it is CU2+(aq) ions which are reduced and not H2Omolecules. Step II Split the redox reaction into its oxidation-half and reduction half-reaction. Oxides of metals and non-metals such as MgO, CrO3, CO2, etc. (i) For acidic and neutral solutions Add H2O molecule to the side deficient in oxygen and H+ to the side deficient in hydrogen. of C. Justify that the following reactions are redox reactions: (b) The possible reaction between Ag+(aq) and Cu(s) is Cu(s) + 2Ag+  (aq)—> Cu2+(aq) + 2Ag(s) Question 9. The reactions taking place in electrochemical cells are redox reactions. N2H4(g) + ClO4(aq) ———–> NO(g) + Cr(aq) Redox reactions grade 11 2. Using PowerPoint lecture notes, present redox reactions to students. (iii) A dilute solution of H2S04with platinum electrodes. (a) Select the possible non-metals that can show disproportionation reaction. The two methods are- Oxidation Number Method & Half-Reaction Method. Question 8. H2S04 is added to an inorganic mixture containing chloride, HCl is produced but if a mixture contains bromide, then we get red vapours of bromine. If, however, excess of O2 is used, the initially formed CO gets oxidised to CO2 in which oxidation state of C is + 4. (i), the sign of the electrode potential as given in Table 8.1 is reversed. of C in cyanate ion, CNO =x-3-2 = -lora: = +4 The four information about the reaction are: Similarly, at the anode, either Ag metal of the anode or H2O molecules may be oxidised. Here, each K atom as lost one electron to form K+ while F2 has gained two electrons to form two F– ions. Slides 3 – 5: Same comments as for Slide 2. (b) ClO4 – does not show disproportionation reaction. (a) Therefore, it is more appropriate to write the equation for photosynthesis as (iii) because it emphasises that 12H2O are used per molecule of carbohydrate formed and 6H2O are produced during the process. The p-Block Elements . In a balanced chemical equation the atoms of various species involved in the reactants and products must be equal in number. Why? Answer: Question 8. Suggest a list of substances where carbon can exhibit oxidation states from -4 to +4 and nitrogen from -3 to +5. Oxidation number for alkali metals is +1 and for alkaline earth metals is + 2. The excess chlorine is removed by treating with sulphur dioxide. If we use a piece of platinum coated with finely divided black containing hydrogen gas absorbed in it. (b) O3(g) + H2O2 (l) ———–> H2O(l) + O2(g) + O2(g) The structure of H2SO5 is In case of coordinate bond, it gives +2 value of oxidation number to less electronegative atom and -2 values to more electronegative atom when coordinate bond is directed formless electronegative atom to more electronegative atom . CuCl2(aq) ——-> CU2+(aq) + 2Cl–(aq) from -1 to zero. A reaction in which oxidation and reduction are carried out separately in two separate half-cells, is known as indirect redox reaction. Reduction half equation: H2O2(aq) + 2H+(aq) + 2e– ———> 2H2O(l) …(ii) What is oxidation number of Fe in [Fe(CO)5] ? Thus, at cathode, either CU2+(aq) or H2O molecules are reduced. Similarly at the anode, either SO42-(aq) ions or H2O molecules are oxidised. Redox Reactions . MnO2 (s) + 4HCl(aq) ——-> MnCl2(aq) + Cl2(aq) + 2H2O Chapter Wise Important Questions Class 11 Chemistry. In other words, the oxidation number of oxidant decreases in a redox reaction. Thus, it is a redox reaction. On the reaction evaluation should be made separately as, The oxidation states of elements exhibiting variable oxidation states are specified by Roman numerals such as I, II, III, IV, etc., within parenthesis after the symbol or name of the element. What is meant by cell potential? 2HBr + H2S04 —–> Br2+ S02 + 2H2O; 2HI + H2S04 ——> I2 + S02 + 2H2O (d) Cr2O72- (aq) + S02 (g)——> Cr3+ (aq) + SO42-(aq) (in acidic solution) Give one example. Redox Reactions Class 11 Notes Chemistry Chapter 8. Answer: (i) C is a reducing agent while O2 is an oxidising agent. For p-block elements [Except F and 0], the highest oxidation number is equal to their group number and lowest oxidation number is equal to the group number minus eight. Answer: Question 9. Question 8. Why? Name the best reducing agent. Question 2. Answer: In the laboratory, benzoic acid is usually prepared by alkaline KMnO4 oxidation of toluene. Chapter 9. In the reaction . (e) 8. (d) 7. Question 2. (ii) The O.N. Further, oxygen is removed from Fe2O3 and added to CO, therefore, Fe2O3 is reduced while CO is oxidised. Justify that this reaction is a redox reaction. Answer: (i) KMnO4 ; K(+l); Mn(+7), 0(-2) 2H2O(Z) + 2e– ————> H2(g) + 2OH–(aq); E° = -0.83 V …(ii) Here O.N. (b) Cs. M4O2 + 4HCI ————-> M4Cl2 + Cl2 + 2H20 Step IV Equalize the total increase or decrease in oxidation number, 8H+ + 4 Mg + 2HNO3 + 8NO3– → 4 Mg (NO3)2 + N2O + 5H2O, 4 Mg + 10 HNO3 → 4 Mg (NO3)2 + N2O + 5H2O, All CBSE Notes for Class 11 Chemistry Maths Notes Physics Notes Biology Notes. Answer: Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if oxidising agent is in excess. Question 20. 2H2O(l) ————–> 02(g) +4H+(aq)+4e– ; E° = -1.23 V …(iv) 160 g of 02 produce NO = 120 g (c) Oxidation half equation: Fe2+(aq) ———> Fe3+(aq) + e– …(i) It may have + or – sign. (i) Intermolecular redox reactions In such reactions, oxidation and reduction take place separately in two compounds. Question 3.Which of the following is most powerful oxidizing agent in the following. Further F reduces Cu2+ to Cu+ but Br does not. Learn more about Oxidation Number, Redox Reactions, Formula for Compounds of NCERT with BYJU'S. This chapter is regarded by many as one of the most important chapters in the CBSE class 11 chemistry syllabus, owing to the fact that the entire field of electrochemistry deals with redox reactions. Reduction half equation: Ag+(aq) +e–———-> Ag(s); E° = +0.80 V …(i) In electrochemical cell anode is written on L.H.S while cathode is written on R.H.S. Play this game to review Chemistry. Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions. 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