Potassium Dichromate & Permanganate — Practice Questions

Free NEET Chemistry multiple-choice questions on Potassium Dichromate & Permanganate. Attempt each question and reveal the answer with a full explanation.

In the acidic medium, which of the following is the correct balanced half-reaction for the reduction of MnO 4 - to Mn 2+ ? MnO 4 - + 8H + + 5e - Mn 2+ + 4H 2O MnO 4 - + 4H + + 3e - MnO 2 + 2H 2O MnO 4 - + 8H + + 3e - Mn 2+ + 4H 2O MnO 4 - + 4H + + 5e - Mn 2+ + 2H 2O When acidified potassium permanganate is used to oxidize Fe 2+ to Fe 3+ , the color change observed is from: Purple to colorless Purple to green Orange to green Pink to blue What happens when a solution of K 2Cr 2O 7 is treated with an excess of NaOH ? The orange color changes to yellow A green precipitate is formed The solution becomes colorless A blue complex is formed When K 2Cr 2O 7 is heated with NaCl and concentrated H 2SO 4 , deep red vapors are evolved. The compound responsible for these vapors is: CrO 2Cl 2 CrCl 3 CrO 3 Na 2CrO 4 Potassium dichromate ( K 2Cr 2O 7 ) is often preferred over Sodium dichromate ( Na 2Cr 2O 7 ) in volumetric analysis (titrations) because: K 2Cr 2O 7 is not hygroscopic, whereas Na 2Cr 2O 7 is K 2Cr 2O 7 is a stronger oxidizing agent K 2Cr 2O 7 is more soluble in water Na 2Cr 2O 7 is cheaper and easier to produce In the titration of oxalic acid against KMnO 4 , the n -factor (valence factor) for KMnO 4 and oxalic acid respectively are: 5 and 2 2 and 5 3 and 2 5 and 1 In the decomposition of Potassium chlorate ( KClO 3 ), Manganese dioxide ( MnO 2 ) is used as a catalyst. At the end of the reaction, MnO 2 is: Unchanged in mass and chemical composition Reduced to Mn 2+ Oxidized to MnO 4 2- Completely consumed In the reaction: MnO 4 - + 8H + + 5e - Mn 2+ + 4H 2O , the n -factor of KMnO 4 is: 5 3 1 2 In the ferrate(VI) ion, FeO 4 2- , which is stable only in strongly alkaline solutions, the oxidation state of Iron is: +6 +4 +3 +8 The color of the manganate ion ( MnO 4 2- ) is: Green Purple Pink Colorless The reaction of toluene with chromyl chloride ( CrO 2Cl 2 ) to give benzaldehyde is known as: Etard reaction Stephen reaction Rosenmund reduction Gattermann-Koch reaction Chromate ion ( CrO 4 2- ) and dichromate ion ( Cr 2O 7 2- ) exist in equilibrium. At what pH is the chromate ion predominantly converted to the dichromate ion? Low pH (Acidic) High pH (Alkaline) pH = 7 (Neutral) pH = 14 (Strongly Basic) Which of the following compounds is used as a 'Primary Standard' in redox titrations? K 2Cr 2O 7 KMnO 4 Na 2Cr 2O 7 NaOH The product obtained when K 2Cr 2O 7 is reacted with H 2O 2 in the presence of sulphuric acid and ether is a deep blue solution. The formula of this blue compound is: CrO 5 Cr 2O 3 CrO 3 CrO 4 2- Which of the following oxoanions of Chromium is stable only in an alkaline medium? CrO 4 2- Cr 2O 7 2- CrO 2 - Cr 2O 3 When acidified KMnO 4 is reacted with KNO 2 (potassium nitrite), the oxidation state of Nitrogen changes from: +3 to +5 +2 to +4 +3 to +4 +5 to +3 Which of the following compounds is used as a 'depolarizer' in dry cells (Leclanché cell)? MnO 2 KMnO 4 PbO 2 CrO 3 What is the n -factor of K 2Cr 2O 7 when it acts as an oxidizing agent in an acidic medium? 6 3 5 2 The reaction of KMnO 4 with oxalic acid ( H 2C 2O 4 ) in acidic medium results in the evolution of which gas? CO 2 CO O 2 H 2 Which of the following does not give oxygen on heating? KClO3 Zn(ClO3)2 K2Cr2O7 (NH4)2Cr2O7 Which one of the following statements is correct when SO2 is passed through acidified K2Cr2O7 solution ? The solution turns blue The solution is decolourized SO2 is reduced Green Cr2(SO4)3 is formed In the neutral or faintly alkaline medium, KMnO4 oxidises iodide into iodate. The change in oxidation state of manganese in this reaction is from +6 to +4 +7 to +3 +6 to +5 +7 to +4 The geometry of the MnO 4 - ion is: Tetrahedral Square planar Octahedral Trigonal bipyramidal What is the oxidation state of Cr in the blue-colored complex formed when K 2Cr 2O 7 reacts with H 2O 2 in an acidic medium? +6 +5 +3 +10 Manganate ion ( MnO 4 2- ) disproportionates in acidic solution to give: MnO 4 - and MnO 2 Mn 2+ and MnO 2 Mn 2+ and MnO 4 - MnO 2 and H 2O In the titration of FeSO 4 with KMnO 4 in the presence of HCl , which of the following occurs? HCl is oxidized to Cl 2 by KMnO 4 HCl acts as a catalyst KMnO 4 is not reduced FeSO 4 is not oxidized Acidified K 2Cr 2O 7 solution turns green when Na 2SO 3 is added to it. This is due to the formation of: Cr 2(SO 4) 3 CrO 4 2- Cr 2(SO 3) 3 CrSO 4 In the preparation of K 2Cr 2O 7 from chromite ore, the first step involves the fusion of the ore with: Na 2CO 3 in the presence of air NaOH in the absence of air H 2SO 4 and K 2SO 4 K 2CO 3 and Al 2O 3 When acidified KMnO 4 reacts with H 2C 2O 4 (oxalic acid), the Mn 2+ ions formed act as a catalyst. This phenomenon is known as: Autocatalysis Homogeneous catalysis Heterogeneous catalysis Induced catalysis In the reaction 2KMnO 4 + 16HCl 2KCl + 2MnCl 2 + 8H 2O + 5X , the product X is: Cl 2 O 2 ClO 2 H 2 The E (M 3+ /M 2+ ) value for chromium is -0.41 V and for manganese is +1.57 V . This indicates that: Cr 2+ is a reducing agent and Mn 3+ is an oxidizing agent Cr 3+ is a reducing agent and Mn 2+ is an oxidizing agent Both Cr 2+ and Mn 3+ are reducing agents Both Cr 2+ and Mn 3+ are oxidizing agents In the dichromate ion ( Cr 2O 7 2- ), the Cr-O-Cr bond angle is approximately: 126 109 180 90 The magnetic nature of MnO 4 2- and MnO 4 - ions respectively are: Paramagnetic, Diamagnetic Diamagnetic, Paramagnetic Both Paramagnetic Both Diamagnetic The chromyl chloride test is used for the detection of: Cl - ions Cr 3+ ions CrO 4 2- ions SO 4 2- ions The reaction of aqueous KMnO 4 with H 2O 2 in acidic conditions gives: Mn 2+ + O 2 MnO 2 + O 2 Mn 2+ + O 3 MnO 4 2- + O 2 Which of the following oxides of Manganese is purely basic? MnO Mn 2O 3 MnO 2 Mn 2O 7 In the volumetric estimation of Fe 2+ ions, which of the following is NOT used to acidify KMnO 4 ? HCl Dilute H 2SO 4 Concentrated H 2SO 4 Both HCl and Concentrated H 2SO 4 When alkaline KMnO 4 reacts with iodide ( I - ), the final oxidation state of Manganese is: +4 +2 +6 +7 The incorrect statement regarding the K 2Cr 2O 7 is: The CrO 4 2- ion is more stable in acidic medium than Cr 2O 7 2- It is used as a primary standard in volumetric analysis It reacts with H 2S to give sulfur The Cr-O terminal bond lengths are shorter than the bridged Cr-O bond lengths The equivalent weight of KMnO 4 in a neutral medium (where MnO 4 - is reduced to MnO 2 ) is (Molecular Weight = M ): M/3 M/5 M/1 M/6 Acidified K 2Cr 2O 7 reacts with H 2S to produce: Colloidal Sulphur SO 2 SO 3 H 2SO 4 Which of the following is an example of a 'disproportionation' reaction of a transition metal oxoanion in acidic medium? 3MnO 4 2- + 4H + 2MnO 4 - + MnO 2 + 2H 2O 2MnO 4 - + 16H + + 5C 2O 4 2- 2Mn 2+ + 10CO 2 + 8H 2O Cr 2O 7 2- + 14H + + 6Fe 2+ 2Cr 3+ + 6Fe 3+ + 7H 2O MnO 2 + 4HCl MnCl 2 + Cl 2 + 2H 2O The number of Cr-O terminal bonds and Cr-O-Cr bridge bonds in the dichromate ion ( Cr 2O 7 2- ) are respectively: 6 and 1 4 and 2 6 and 2 3 and 1 The E (M 3+ /M 2+ ) value is highly positive for Manganese ( +1.57 V ) because: Mn 2+ has a stable d 5 configuration Mn 3+ has a stable d 4 configuration Mn 2+ is easily oxidized Manganese has high enthalpy of atomization What are the products formed when potassium permanganate ( KMnO 4 ) is heated at 513 K ? K 2MnO 4, MnO 2, O 2 K 2MnO 4, MnO, O 2 KMnO 2, MnO 2, O 3 K 2MnO 4, Mn 2O 7, O 2 In the volumetric analysis of oxalic acid using KMnO 4 , the solution is heated to about 60 C to: Increase the rate of reaction Make the endpoint sharper Prevent the decomposition of KMnO 4 Increase the solubility of MnSO 4 The color of K 2CrO 4 changes to orange on addition of an acid. This is because of the formation of: Cr 2O 7 2- Cr 3+ CrO 3 CrO 5 Which of the following products is formed when KMnO 4 is treated with H 2S in acidic medium? Sulfur SO 2 SO 3 H 2SO 4 In the chromyl chloride test, the final yellow precipitate formed when the vapors are passed into NaOH and then treated with lead acetate is: PbCrO 4 PbCl 2 Na 2CrO 4 CrO 2Cl 2 What is the oxidation state of Manganese in the product formed when KMnO 4 is heated with solid KOH at high temperatures? +6 +4 +2 +7 What is the product formed when KMnO 4 reacts with SO 2 in an acidic medium? H 2SO 4 and Mn 2+ S and Mn 2+ Na 2SO 3 and MnO 2 H 2S and Mn 2+ Which of the following properties makes Potassium dichromate ( K 2Cr 2O 7 ) more suitable than Sodium dichromate ( Na 2Cr 2O 7 ) for use as a primary standard in volumetric analysis? It is non-hygroscopic in nature It is more soluble in water It has a lower molecular mass It is a stronger oxidizing agent The intense purple color of the permanganate ion ( MnO 4 - ) is attributed to: Ligand-to-Metal Charge Transfer (LMCT) d-d transition Metal-to-Ligand Charge Transfer (MLCT) f-f transition What is the product of the thermal decomposition of Potassium dichromate ( K 2Cr 2O 7 )? K 2CrO 4, Cr 2O 3 and O 2 CrO 3 and K 2O K 2CrO 4 and CrO 3 KMnO 4 and O 2 In the dichromate ion ( Cr 2O 7 2- ), the hybridization of the bridging oxygen atom is: sp 3 sp 2 sp dsp 2 The structure of the dichromate ion ( Cr 2O 7 2- ) consists of: Two tetrahedra sharing one corner Two tetrahedra sharing one edge Two tetrahedra sharing one face One tetrahedron and one octahedron When SO 2 gas is passed through an acidified solution of K 2Cr 2O 7 , the solution turns green. The balanced equation for the reduction half-reaction is: Cr 2O 7 2- + 14H + + 6e - 2Cr 3+ + 7H 2O SO 2 + 2H 2O SO 4 2- + 4H + + 2e - Cr 2O 7 2- + 8H + + 6e - 2Cr 3+ + 4H 2O CrO 4 2- + 4H 2O + 3e - Cr(OH) 3 + 5OH - In the alkaline dry cell (battery), the cathode reaction involves the reduction of: MnO 2 to MnO(OH) Zn to ZnO PbO 2 to PbSO 4 NiO(OH) to Ni(OH) 2 When KMnO 4 reacts with H 2O 2 in an acidic medium, the gas evolved is: O 2 H 2 CO 2 O 3 What is the hybridisation of Manganese in the MnO 4 2- ion? sp 3 dsp 2 d 2sp 3 sp 3d The preparation of potassium permanganate ( KMnO 4 ) involves the alkaline oxidative fusion of pyrolusite ore ( MnO 2 ). What is the color and oxidation state of the intermediate compound formed after fusion with KOH in the presence of O 2 ? Dark green, +6 Purple, +7 Light pink, +2 Brown, +4 The reaction of dilute Nitric acid ( HNO 3 ) with Copper metal yields which gas? NO NO 2 N 2O H 2 The structure of the Manganate ion ( MnO 4 2- ) involves which type of hybridization and magnetic nature? sd 3 , Paramagnetic sp 3 , Diamagnetic dsp 2 , Paramagnetic d 2sp 3 , Diamagnetic What is the product formed when KMnO 4 reacts with an excess of KI in a strongly alkaline medium? IO 3 - I 2 I 3 - I - In the reaction Cr 2O 7 2- + H 2O 2CrO 4 2- + 2H + , what happens when the pH of the solution is increased? The equilibrium shifts to the right, forming yellow chromate. The equilibrium shifts to the left, forming orange dichromate. No change occurs. Chromium undergoes disproportionation. KMnO4 can be prepared from K2MnO4 as per the reaction: 3 MnO4 2- + 2 H2O <=> 2 MnO4 - + MnO2 + 4 OH - The reaction can go to completion by removing OH - ions by adding HCl KOH CO2 SO2 In the reaction Cr 2O 7 2- + 14H + + 6I - 2Cr 3+ + 3I 2 + 7H 2O , which species is acting as the reducing agent? I - Cr 2O 7 2- H + Cr 3+ In acidic medium, H2O2 changes Cr2O7 2- to CrO5 which has two (-O-O) bonds. Oxidation state of Cr in CrO5 is :- + 5 + 3 + 6 - 10 The reaction of aqueous KMnO4 with H2O2 in acidic conditions gives :- Mn 4+ and O2 Mn 2+ and O2 Mn 2+ and O3 Mn 4+ and MnO2 The manganate and permanganate ions are tetrahedral, due to : The -bonding involves overlap of d-orbitals of oxygen with d-orbitals of manganese The -bonding involves overlap of p-orbitals of oxygen with d-orbitals of manganese There is no -bonding The -bonding involves overlap of p-orbitals of oxygen with p-orbitals of manganese What is the product formed when KMnO 4 reacts with I - in a neutral or faintly alkaline medium? IO 3 - I 2 I 3 - IO 4 - The purple color of KMnO 4 is due to: L M charge transfer transition d-d transition M L charge transfer transition - transition What is the change in the oxidation state of Manganese when KMnO 4 is reduced in a strongly alkaline medium? From +7 to +6 From +7 to +4 From +7 to +2 From +7 to +3 The number of moles of KMnO 4 reduced by one mole of KI in alkaline medium is: 2 1 5 0.2 When KMnO 4 reacts with thiosulfate ( S 2O 3 2- ) in a neutral or faintly alkaline medium, the product formed is: SO 4 2- S S 4O 6 2- SO 3 2- What is the number of moles of KMnO 4 required to oxidize one mole of ferrous oxalate ( FeC 2O 4 ) in an acidic medium? 3/5 2/5 1/5 5/3 The yellow color of the chromate ion ( CrO 4 2- ) and orange color of dichromate ion ( Cr 2O 7 2- ) is primarily due to: Ligand to metal charge transfer ( LMCT ) d-d transitions Metal to ligand charge transfer ( MLCT ) f-d transitions In the MnO 4 - ion, the four Mn-O bonds are equivalent due to: Resonance Hyperconjugation p -p bonding only Octahedral geometry When K 2Cr 2O 7 reacts with cold, concentrated H 2SO 4 , which of the following is formed? CrO 3 Cr 2(SO 4) 3 CrO 2Cl 2 Cr 2O 3 Identify the correct statement about MnO 4 2- (manganate ion). It is green in color and paramagnetic It is purple in color and diamagnetic It is green in color and diamagnetic It is purple in color and paramagnetic When KMnO 4 is treated with cold concentrated H 2SO 4 , an explosive oil-like compound is formed. This compound is: Mn 2O 7 MnO 2 MnSO 4 Mn 2O 3 In the dichromate ion ( Cr 2O 7 2- ), there are two types of Cr-O bonds. Which of the following is true regarding their bond lengths? The terminal Cr-O bonds are shorter than the bridging Cr-O-Cr bonds All Cr-O bonds are of equal length due to resonance The terminal Cr-O bonds are longer than the bridging Cr-O-Cr bonds The terminal bonds have a bond order of 1 Among the following oxoanions, which one is expected to be colorless? ReO 4 - MnO 4 - CrO 4 2- FeO 4 2- The green paramagnetic species formed by heating KMnO4 at 513 K is K2MnO4 Mn3O4 MnO KO2 When KMnO 4 is added to a solution of Sn 2+ in acidic medium, the Sn 2+ is converted to: Sn 4+ Sn SnO 2 Sn 3+