Tag: changes - physical and chemical
Questions Related to changes - physical and chemical
Maximum conductivity would be of :
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$K _{3}Fe(CN) _{6}[0.1 M Solution]$
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$K _{3}Ni(CN) _{6}[0.1 M Solution]$
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$FeSO _{4}.Al _{2}(SO _{4}) _{3}.24H _{2}O[0.1 M Solution]$
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$Na _{3}[Ag(S _{2}O _{3}) _{2}][0.1 M Solution]$
When the lead accumulator is charged, it acts as:
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an electrolytic cell
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a galvanic cell
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a Daniel cell
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none of the above
During the charging of a lead accumulator cell, the electical energy is stored in the form of chemical energy. Thus, the electrical energy derives non-spontaneous chemical reactions. Hence, during charging, the lead accumulator cell acts as an electrolytic cell.
When lead storage battery is charged:
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lead dioxide dissolves
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sulphuric acid is regenerated
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lead electrode becomes coated with lead sulphate
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the concentration of sulphuric acid decreases
During charging of lead storage battery, sulphuric acid is regenerated. The net cell reaction during charging is $ PbS{ O } _{ 4 } +{ 2{ H } _{ 2 }O } \xrightarrow { } Pb + Pb{ O } _{ 2 } + 2{ H } _{ 2 }{ SO } _{ 4 } $
Number of Faradays involved in the net reaction of Lead accumulator is __________.
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1
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0.5
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2
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cannot be predicted
For lead accumulator battery, the oxidation reaction at anode requires two moles of electrons. Similarly, the reduction reaction at cathode requires two moles of electrons. Hence, the number of Faradays involved in the net reaction of Lead accumulator is 2.
Note: 1 Faraday is equal to the amount of charge on 1 mole of electrons.
During the charging of lead accumulator battery voltage varies from:
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$2.15$ V to $1.88$ V
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$1.88$ V to $2.0$ V
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$1.88$ V to $2.15$ V
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does not change
When the lead accumulator battery is charged, the voltage range is 1.88 V to 2.15 V as the concentration of sulphuric acid varies from 5% to 40%.
In electrochemical passivity:
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thin visible oxide film is formed
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thin invisible oxide film is formed
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thick visible oxide film is formed
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thick invisible oxide films formed
During electrochemical passivisation, the metal surface is made inactive by formation of thin invisible oxide layer on the surface.
Iron is not protected from rusting by:
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galvanization
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electroplating with $Ni$ or $Cr$
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heating the iron to redness in steam
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treating it with $H _{3}PO _{4}$
Phosphoric acid will not form a protective coating of iron oxide on the surface of iron. A strong oxidizing agent such as nitric acid is required for this process.
The technique of protecting a metal from corrosion by connecting it to a second metal (that is more easily oxidized) is called:
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galvanization
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anodic protection
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cathodic protection
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sacrificial protection
In cathodic protection, the more easily oxidized metal is attached to the metal which is to be protected. This results in corrosion of more easily oxidized metal. The other metal is thus protected from corrosion.
Iron can be prevented from rusting by:
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connecting iron to more electropositive metal a case of cathodic protection.
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connecting iron to more electropositive metal a case of anodic protection.
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connecting iron to less electropositive metal a case of anodic protection.
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connecting iron to less electropositive metal a case of cathodic protection.
Cathodic protection: A technique to control corrosion of a metal surface by making it work as a cathode of an electrochemical cell by placing in contact with the metal to be protected another more easily corroded metal to act as the anode of the electrochemical cell. Most commonly used to protect steel, water pipelines, and storage tanks.
Anodic protection: A technique to control corrosion of a metal by making it work as anode developing a passive film on the metal. It used in extremely corrosive conditions and most extensively used to store and handle sulphuric acid container.
Hence, option A and C are correct
Which of the following statements is/are incorrect ?
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Rust is $Fe _{2}O _{3}$
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Zn - Cu cell is called Daniell cell.
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Saline water slows down rusting.
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Pure metals undergo corrosion faster than impure metals.
Correct statements are given below:
b. Correct.
c. Saline water fastens the rusting.
d. Pure metals undergo corrosion slower than impure metals.