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Redox Reactions And Electro Chemistry Mcq
Quiz 5
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Q.1
The brown ring complex is formulated as [Fe(H2O5NO+]SOthe oxidation number of iron is .. [ IIT 1987]
0%
a)1
0%
b) 2
0%
c)3
0%
d)0
Explanation
Answer: (a)
Q.2
The oxidation number in S8, S2F2, H2S respectively are [IIT 1999]
0%
a)0, +1 and -2
0%
b) +2, +1 and -2
0%
c)0, +1 and +2
0%
d)-2, +1 and -2
Explanation
Answer: (a)
Q.3
The reaction of KMnO4 and HCl results is [ CPMT 2000]
0%
a)Oxidation of Mn in KMnO4 and production of Cl2
0%
b) reduction of Mn in KMnO4 and production of H2
0%
c)Oxidation of Mn in KMnO4 and production of H2
0%
d)Reduction of Mn in KMnO4 and production of Cl2
Explanation
2KMnO4 +16HCl → 2KCl +2MnCl2 + 8H2O + 5Cl2 Here oxidation number of Mn decreases from +7 to +2 and oxidation number of Chlorine increases from -1 to 0 Answer:(d)
Q.4
On reduction of KMnO4 by oxalic acid in acidic medium, the oxidation number of Mn changes. What is the magnitude of this change? [ MP PMT 2000]
0%
a) From 7 to 2
0%
b) From 6 to 2
0%
c) From 5 to 2
0%
d) From 7 to 4
Explanation
MnO4- + 8H+ +5e- → Mn2+ + 4H2O Here oxidation number of Mn changes from +7 in KMnO4 to +2 in Mn2+ Answer: (a)
Q.5
The oxidation state of chromium in potassium dichromate (K2Cr2O7) is ..[AFMC 1999]
0%
a)-5
0%
b) +6
0%
c)+2
0%
d)-2
Explanation
Answer: (b)
Q.6
Consider the following reaction5H2O2 + xClO2 +2OH- → xCl- +yO2 + 6H2OThe reaction is balanced is ...[CPMT 2000]
0%
a) x=5, y=2
0%
b) x=2, y=5
0%
c)x=4, y=10
0%
d)x=5, y=5
Explanation
Answer: (b)
Q.7
the set of numerical coefficients that balance the equation K2CrO4 + HCl → K2Cr2O7 + KCl + H2O is [kerala CEE 2001]
0%
a) 1, 1, 2, 2, 1
0%
b) 2, 2, 1, 1, 1
0%
c)2, 1, 1, 2, 1
0%
d)2, 2, 1, 2, 1
Explanation
Answer:(d)
Q.8
oxidation number of S in H2S2O8 is [ MP PMT 2002]
0%
a) +2
0%
b) +4
0%
c) +6
0%
d) +7
Explanation
Sulphuric acid contain one peroxide link thus two atoms of oxygen have oxidation number -1 each remaining have -2 thus 2×(+1) + 2x + 6×(-2) +2 ×(-1)=0 ∴x=+6 Answer: (c)
Q.9
The oxidation state of osmium (OS) in OsO4 is [ AIIMS 1999]
0%
a)+7
0%
b) +6
0%
c)+4
0%
d)+8
Explanation
Answer: (d)
Q.10
Which of the following molecules can acts as an oxidising as well as reducing agent? [ kerala MEE2000]
0%
a) H2S
0%
b) SO3
0%
c)H2O2
0%
d)H2SO4
Explanation
Sulphur exhibits oxidation numbers of -2, 0, +2, +4 and +6, In first option oxidation state of S is -2 thus can not reduce further , in second 'b' option sulphur oxidation state is +6 hence can not increase , and in fourth option oxidation state of S is +6 can not increase furtherBut incase of H2O2 oxidation state of Oxygen can be reduced to -1 to -2 and increase from -1 to 0 thus option 'c' is correctAnswer: (c)
Q.11
The oxidation states of sulphur in the SO3-, S2O42- and S2O62- follows the order
0%
a)S2O4-2
0%
b)SO3 2-
0%
c)S2O4-2
0%
d)S2O62-
Explanation
Oxidation number in SO3-=+4S2O42-=+3S2O62-=+5 Answer:(a)
Q.12
Student states that burning of lime is an oxidation process. the reason he sites is that an oxide of metal is produced on burning Which of the following statement about the above reaction is correct?
0%
a) Both the statement and reason are correct and reason are the correct explanation of the statement
0%
b) Both the statement and reason are correct and reason are the correct but reason is not correct explanation of the statement
0%
c) The statement is correct but the reason is incorrect
0%
d) The statement is incorrect but reason is correct
Explanation
Lime is CaCO3 on heating it produces CaO ( Metal oxide) CaCO3 → CaO +CO2 thus Statement burning of lime is oxidation is incorrect but the reason is correct Answer: (d)
Q.13
Of the following reactions, only one is a redox reaction. identify it [ CPMT 2000]
0%
a)Ca((OH)2 + 2HCl → CaCl2 + 2H2O
0%
b) BaCl2 +MgSO4 → BaSO4 + MgCl2
0%
c)2S2O72- + 2H2O → 4SO42- + 4H+
0%
d)Cu2S + 2FeO → 2Cu + SO2
Explanation
In option 'd' Oxidation number of Cu changed from +1 to 0, Fe Changed from +2 to 0 S changed from -2 to +4 thus option 'd' is redox reactionAnswer: (d)
Q.14
Equivalent mass of oxidising agent in the reactionSO2 + 2H2S → 3S + 2H2O [ DEC 2000]
0%
a) 32
0%
b) 64
0%
c)16
0%
d)8
Explanation
in given equation oxidation number of S increased by 4 thus equivalent weight=molecular weight/4=64/4=16Answer: (c)
Q.15
For the reactionMx+ + MnO4- → MO3- +Mn2+ + ½ O2If one mole of MnO4- oxidises 1.67moles of Mx+ to Mn3-, then the value of x in the reaction is
0%
a)5
0%
b)3
0%
c)2
0%
d)1
Explanation
Oxidation number of Mn is reduced by 5 thus five electrons are accepted by the Mn which are released by 1.67 moles of Mx+ ∴ 1 mole of Mx+ will lose electrons=5/167=3/ mole(approx) Since Mx+ changes to MO3- Oxidation number of M is +5 in MO3- ∴ x + 3=5 , x=2 Answer:(c)
Q.16
Number of moles of KMnO4 required to oxidise one mole of Fe(C2O4) in acidic medium is
0%
a) 0.6
0%
b) 1.67
0%
c) 0.2
0%
d) 0.4
Explanation
Fe(C2O4) ↔ Fe2+ + C2O4- both Fe2+ and C2O4- are oxidised by MnO4- in acidic medium Fe2+ → Fe3+ +e- C2O4- → 2CO2 + 2e- Thus Fe(C2O4) → Fe3+ +2CO2 + 3e- Balanced redox reaction will be 3MnO4- + 24H+ +5Fe3+ + 10CO2 +12H2O Thus 5Fe(C2O5)=3MnO4- ∴ 1Fe(C2O4)=3/5 MnO4-=0.6 MnO4- Answer: (a)
Q.17
A metal ion M3+ loses 3 electrons, its oxidation number will be [ CPMT 1999]
0%
a)+3
0%
b) +6
0%
c)0
0%
d)-3
Explanation
M3+ → M6+ + 3e-Thus oxidation number of metal is +6Answer: (b)
Q.18
The oxidation number of iron in Fe3O4 is [ CBE PMT 1999]
0%
a) +2
0%
b) +3
0%
c)8/3
0%
d)2/3
Explanation
Answer: (c)
Q.19
The chemical that undergoes self oxidation and self reduction in the same reaction is [ Tamil nadu CET 20001]
0%
a) benzyl alcohol
0%
b) acetone
0%
c)formaldehyde
0%
d)acetic acid
Explanation
Formaldehyde (HCHO) is reduced to CH3OH and also it is oxidized to HCOOH in Cannizzaro's reaction in presence of Conc. NaOH solution ( disproportionate reaction) 2HCHO + NaOH (50%) → CH3OH + HCOONa Answer:(c)
Q.20
In which of the following complexes, oxidation state of metal is zero? [ MPPET 1998]
0%
a) [Pt(NH2)2Cl2]
0%
b) [Cr(CO)6]
0%
c) [Cr(NH3)3Cl3]
0%
d) [Ce(en)2Cl2]
Explanation
Oxidation state of metal in metal carbonyls is zeroAnswer: (b)
Q.21
Which statement is not correct? [ MPCET1999]
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a)Potassium permanganate is a powerful oxidising substance
0%
b) Potassium permanganate is a weaker oxidising agent than potassium dichromate
0%
c)Potassium permanganate is a stronger oxidising agent than potassium dichromate
0%
d)Potassium dichromate oxidises a secondary alcohol into ketone
Explanation
KMnO4 can gains 5e- per mole while K2Cr2O7 gains 6e- per mole. therefore potassium permanganate is weaker oxidising agent than potassium dichromateAnswer: (c)
Q.22
In the chemical reaction Ag2O + H2O + 2e- → 2Ag + 2OH- [kerala CEE 2000]
0%
a) Water is oxidised
0%
b) Electrons are reduced
0%
c)Silver is oxidised
0%
d)silver is reduced
Explanation
Answer: (d)
Q.23
When KMnO4 acts as an oxidising agent and ultimately form MnO4-2, MnO2, Mn2O3 and Mn+2, then the number of electrons transferred in each case respectively is [ AIEEE 2002]
0%
a) 4, 3, 1, 5
0%
b) 1, 5, 3, 7
0%
c)1, 3, 4, 5
0%
d)3, 5, 7, 1
Explanation
Oxidation number in KMnO4=+7 MnO4-2=+6MnO2=4Mn2O3=+3Mn+2=+2 Answer:(c)
Q.24
A compound of Xe and F is found to have 53.3% Xe(atomic weight=133). Oxidation number of Xe in this compound is
0%
a) +2
0%
b) 0
0%
c) +4
0%
d) +6
Explanation
Number of Atoms of Xe 53.3/133=0.398 Number of atoms of F 46.7/19=2.45 Taking ration as 2.45 /0.398=6/1 Thus Xe one atom and Fe 6 atom formula is XeF6 Oxidation number of Xe is +6 Answer: (d)
Q.25
The oxidation number of Cobalt in K2[Co(NO2)6] is .. [ EAMCE 1998]
0%
a)0
0%
b) +4
0%
c)+3
0%
d)+6
Explanation
Answer: (c)
Q.26
What is the coefficient of oxalate ion in the following reaction?MnO4- + C2O42- + H+ → Mn2+ + CO2 + H2O [ JIPMER 1999]
0%
a) 4
0%
b) 2
0%
c)3
0%
d)5
Explanation
Balance equation[MnO4- + 8H+ + 5e- → Mn + 4H2] × 2[C2O42- → 2CO2 +2e-] × 5 Add above two equations coefficient of oxalate ion is 5Answer: (d)
Q.27
Which of the following is not reducing agent? [ DEC 2000]
0%
a) SO2
0%
b) H2O2
0%
c)CO2
0%
d)NO2
Explanation
Incase of option 'c' oxidation state of C is +4 and can not be increased further thus can not act as reducing agent Answer:(c)
Q.28
In the reaction 2KMn4 +16HCl → 5Cl2 + 2MnCl2 +2KCl + 8H2Othe reduced product is [ kerala MEE 2003]
0%
a) Cl2
0%
b) MnCl2
0%
c) H2O
0%
d) KCl
Explanation
Mn in above reaction reduced thus MnCl2 is reduced product Answer: (b)
Q.29
If molecular weight of KMnO4 is 'M' then its equivalent weight in acidic medium would be .. [ MP PMT 1998]
0%
a)M
0%
b) M/2
0%
c)M/5
0%
d)M/4
Explanation
MnO4- + 8H+ +5e- → Mn + 4H2OIt is five-electron exchange thus equivalent weight=M/5Answer: (c)
Q.30
In H2O2, the oxidation state of oxygen is [ CPMT 2000]
0%
a) -2
0%
b) -1
0%
c)0
0%
d)-4
Explanation
bonding is H-O-O-H Answer: (b)
0 h : 0 m : 1 s
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