Chapter Chosen

Cell : the unit of life

Book Store

Download books and chapters from book store.
Currently only available for.
CBSE

Previous Year Papers

Download the PDF Question Papers Free for off line practice and view the Solutions online.
Currently only available for.
Class 10 Class 12
Split the following redox reactions in oxidation and reduction half reactions:
left parenthesis straight a right parenthesis space 2 straight K left parenthesis straight s right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space space 2 KCl left parenthesis straight s right parenthesis
left parenthesis straight b right parenthesis space 2 Al left parenthesis straight s right parenthesis space plus space 3 Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space space rightwards arrow space space space 2 Al to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space 3 Cu left parenthesis straight s right parenthesis

(a) The given reaction
             2 straight K left parenthesis straight s right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis space space space rightwards arrow space space space 2 KCl left parenthesis straight s right parenthesis
can space be space split space into space two space half space reaction space as colon
(i) Oxidation half-reaction.
                               2 straight K space rightwards arrow space space 2 straight K to the power of plus space plus space 2 straight e to the power of minus
(ii) Reduction half reaction:
                              Cl subscript 2 space plus space 2 straight e to the power of minus space space rightwards arrow space space space 2 Cl to the power of minus

(b) The given reaction
          2 Al left parenthesis straight s right parenthesis space plus space 3 Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space space space rightwards arrow space space space 2 Al to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space 3 Cu left parenthesis straight s right parenthesis
can space be space split space into space two space half space reaction colon
(i) Oxidation half reaction:
                    2 Al left parenthesis straight s right parenthesis space space rightwards arrow space space space 2 Al to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus 6 straight e to the power of minus
(ii) Reduction half reaction:
               3 Cu to the power of 2 plus end exponent space plus space 6 straight e to the power of minus space space space rightwards arrow space space space 3 Cu left parenthesis straight s right parenthesis


How will you represent an electrochemical cell with the help of cell notation or cell diagram?

A galvanic cell can always be represented by a cell diagram.

(i) The anode is written on the left-hand side and represented by writing metal first and then the metal ions (or electrolyte). The two are separated by a vertical line.
Zn | Zn2+ (1M)
Pt, H2(1 atm); H+(1M)

(ii) The cathode is written on the right-hand side and is represented by writing metal ions (or electrolyte) first and then metal (or solid phase). The two are separated by a vertical line.
Cu2+ (1M) | Cu

(iii) The salt bridge is represented by two vertical lines separating the two half cells. Daniell cell is represented as;

Zn | Zn2+ 1M) || Cu2+ (1M) | Cu


Write the anode reaction, the cathode reaction and the net cell reaction for the following cells. Which electrode will be the positive terminal in each cell?
1. space space Zn left parenthesis straight s right parenthesis space vertical line space space Zn to the power of 2 plus end exponent space vertical line vertical line space Br to the power of minus comma space space space Br subscript 2 space vertical line space Pt left parenthesis straight s right parenthesis
2. space space space Cr left parenthesis straight s right parenthesis space vertical line space Cr to the power of 3 plus end exponent space vertical line vertical line space straight I to the power of minus comma space space straight I subscript 2 space straight I space Pt left parenthesis straight s right parenthesis
3. space space space Pt left parenthesis straight s right parenthesis space vertical line space straight H subscript 2 left parenthesis straight g right parenthesis comma space straight H to the power of plus left parenthesis aq right parenthesis space vertical line vertical line space Cu to the power of 2 plus end exponent vertical line space Cu left parenthesis straight s right parenthesis.

1.   For the cell
    Zn left parenthesis straight s right parenthesis space plus space Zn to the power of 2 plus end exponent space vertical line vertical line space Br to the power of minus comma space space Br subscript 2 vertical line space Pt left parenthesis straight s right parenthesis
the space two space half space reactions space can space be space represented space as colon
left parenthesis straight i right parenthesis space Anode space reaction space left parenthesis oxidation space half space reaction right parenthesis colon
space space space space space space space space space space Zn left parenthesis straight s right parenthesis space space space rightwards arrow space space space Zn to the power of 2 plus end exponent space plus space 2 straight e to the power of minus
left parenthesis ii right parenthesis space Cathode space reaction space left parenthesis Reduction space half space reaction right parenthesis colon
space space space space space space space space space space space space Br subscript 2 plus space 2 straight e to the power of minus space rightwards arrow space 2 Br to the power of minus
Net space cell space reaction space left square bracket by space adding space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis right square bracket colon
space space space space space space space space Zn left parenthesis straight s right parenthesis space plus space Br subscript 2 space space rightwards arrow space space space Zn to the power of 2 plus end exponent space plus space 2 Br to the power of minus
Positive terminal:   The bromine electrode where reduction takes place.

2. For the cell Cr left parenthesis straight s right parenthesis space plus space Cr to the power of 3 plus end exponent space parallel to space space straight I to the power of minus comma space space straight I subscript 2 space vertical line space Pt left parenthesis straight s right parenthesis
The two half reactions can be represented as:
(i) Anode reaction (oxidation half reaction):
                Cr left parenthesis straight s right parenthesis space rightwards arrow space space space Cr to the power of 3 plus end exponent space left parenthesis aq right parenthesis space plus space 3 straight e to the power of minus
(ii) Cathode reaction (reduction half reaction):
               straight I subscript 2 space plus space 2 straight e to the power of minus space space space rightwards arrow space space 2 straight I to the power of minus
Net cell reaction: It is obtained by multiplying equation (i) by 2 and equation (ii) by 3 and then adding.
2 Cr left parenthesis straight s right parenthesis space space space rightwards arrow space space space space 2 Cr to the power of 3 plus end exponent space plus space 6 straight e to the power of minus
3 straight l subscript 2 left parenthesis straight s right parenthesis space plus space 6 straight e to the power of minus space space rightwards arrow space space space 6 straight I to the power of minus
2 Cr left parenthesis straight s right parenthesis space plus space 3 straight I subscript 2 left parenthesis straight s right parenthesis space rightwards arrow space space 2 Cr to the power of 3 plus end exponent space plus space 6 straight I to the power of minus

Positive terminal. The iodine electrode where reduction takes place.

3. For cell Pt left parenthesis straight s right parenthesis vertical line space straight H subscript 2 left parenthesis straight g right parenthesis comma space straight H to the power of plus left parenthesis aq right parenthesis space parallel to space Cu to the power of 2 plus end exponent space vertical line space Cu left parenthesis straight s right parenthesis
the two half reactions can be represented as:
(i) Anode reaction (oxidation half reaction):
                     straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space space 2 straight H to the power of plus left parenthesis aq right parenthesis space plus space 2 straight e to the power of minus
(ii) Cathode reaction (reduction half reaction):
                   Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight e to the power of minus space space space rightwards arrow space space space Cu left parenthesis straight s right parenthesis
Net cell reaction:  It is obtained by adding equations (i) and (ii).
straight H subscript 2 left parenthesis straight g right parenthesis space plus space Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space rightwards arrow space space 2 straight H to the power of plus left parenthesis aq right parenthesis space plus space Cu left parenthesis straight s right parenthesis
Positive terminal: The copper electrode where reduction takes place.


What do you mean by redox couple ?


A redox couple may be defined as a combination of the oxidised and reduce forms of the same substance taking part in an oxidation or reduction half reactions. A redox couple is usually represented by separating the oxidised form and the reduced form of a vertical line which represents the interface (solid/solution). For example, in a galvanic cell, the two redox couples are represented as Zn2+/Zn and Cu2+/Cu. In both cases, oxidised form is put before the reduced form.

Consider the following reactions which produce electricity in a galvanic cell:
left parenthesis straight i right parenthesis space 2 Fe to the power of 2 plus end exponent space plus space Cl subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space space 2 Fe to the power of 3 plus end exponent space plus space 2 Cl to the power of minus
left parenthesis ii right parenthesis space Cd left parenthesis straight s right parenthesis space plus space straight I subscript 2 space space space rightwards arrow space space space space Cd to the power of 2 plus end exponent space plus space 2 straight I to the power of minus
left parenthesis iii right parenthesis space 2 Cr left parenthesis straight s right parenthesis space plus space 3 Cu to the power of 2 plus end exponent space rightwards arrow space space 3 Cu left parenthesis straight s right parenthesis space plus space 2 Cr to the power of 3 plus end exponent
Write the anode and cathode reactions for galvanic cell. Specify the nature of anodes and cathodes. Write the cell in the usual notation.

bold 1 bold. bold space bold 2 bold Fe to the power of bold 2 bold plus end exponent bold space bold plus bold space bold Cl subscript bold 2 bold left parenthesis bold g bold right parenthesis bold space bold space bold rightwards arrow bold space bold space bold space bold 2 bold Fe to the power of bold 3 bold plus end exponent bold space bold plus bold space bold 2 bold Cl to the power of bold minus
bold left parenthesis bold i bold right parenthesis bold space bold Anode bold space bold reaction bold space bold left parenthesis bold Oxidation bold space bold half bold space bold reaction bold right parenthesis bold colon
bold space bold space bold space bold space bold space bold 2 bold Fe to the power of bold 2 bold plus end exponent bold space bold space bold space bold space bold rightwards arrow bold space bold space bold space bold space bold 2 bold Fe to the power of bold 3 bold plus end exponent bold space bold plus bold space bold 2 bold e to the power of bold minus
bold left parenthesis bold ii bold right parenthesis bold space bold Cathode bold space bold reaction bold space bold left parenthesis bold Reduction bold space bold half bold space bold reaction bold right parenthesis
bold space bold space bold space bold space bold space bold space bold space bold space bold Cl subscript bold 2 bold space bold plus bold space bold 2 bold e to the power of bold minus bold space bold space bold rightwards arrow bold space bold space bold space bold 2 bold Cl to the power of bold minus
bold therefore bold space bold space bold space bold space bold Cell bold space bold notation bold space bold is bold space bold Fe to the power of bold 2 bold plus end exponent bold space bold vertical line bold space bold Fe to the power of bold 3 bold plus end exponent bold space bold vertical line bold vertical line bold space bold Cl to the power of bold minus bold comma bold space bold space bold Cl subscript bold 2 bold space bold vertical line bold space bold Pt bold left parenthesis bold s bold right parenthesis

bold 2 bold. bold space bold space bold Cd bold left parenthesis bold s bold right parenthesis bold space bold plus bold space bold I subscript bold 2 bold space bold space bold space bold rightwards arrow bold space bold space bold space bold Cd to the power of bold 2 bold plus end exponent bold space bold plus bold space bold 2 bold I to the power of bold minus
bold left parenthesis bold i bold right parenthesis bold space bold Andoe bold space bold reaction bold space bold left parenthesis bold oxidation bold space bold half bold space bold reaction bold right parenthesis bold colon
bold space bold space bold space bold space bold space bold space bold Cd bold left parenthesis bold s bold right parenthesis bold space bold space bold space bold rightwards arrow bold space bold space bold space bold Cd to the power of bold 2 bold plus end exponent bold space bold plus bold space bold 2 bold e to the power of bold minus
bold left parenthesis bold ii bold right parenthesis bold space bold Cathode bold space bold reaction bold space bold left parenthesis bold Reduction bold space bold half bold space bold reaction bold right parenthesis bold colon
bold space bold space bold space bold space bold space bold space bold I subscript bold 2 bold space bold plus bold space bold 2 bold e to the power of bold minus bold space bold space bold space bold rightwards arrow bold space bold space bold space bold 2 bold I to the power of bold minus
bold therefore bold space bold space bold space bold space bold Cell bold space bold notation bold space bold is bold space bold Cd bold vertical line bold Cd to the power of bold 2 bold plus end exponent bold space bold vertical line bold vertical line bold space bold I to the power of bold minus bold comma bold space bold space bold I subscript bold 2 bold space bold Pt bold left parenthesis bold s bold right parenthesis

bold 3 bold. bold space bold space bold 2 bold Cr bold left parenthesis bold s bold right parenthesis bold space bold plus bold space bold 3 bold Cu to the power of bold 2 bold plus end exponent bold space bold space bold rightwards arrow bold space bold space bold space bold 3 bold Cu bold left parenthesis bold s bold right parenthesis bold space bold plus bold space bold 2 bold Cr to the power of bold 3 bold plus end exponent
bold left parenthesis bold i bold right parenthesis bold space bold Anode bold space bold reaction bold space bold left parenthesis bold oxidation bold space bold half bold space bold reaction bold right parenthesis bold colon
bold space bold space bold space bold space bold space bold space bold space bold space bold 2 bold Cr bold left parenthesis bold s bold right parenthesis bold space bold rightwards arrow bold space bold space bold space bold 2 bold Cr to the power of bold 3 bold plus end exponent bold space bold plus bold space bold 6 bold e to the power of bold minus
bold left parenthesis bold ii bold right parenthesis bold space bold Cathode bold space bold reaction bold space bold left parenthesis bold Reduction bold space bold half bold space bold reaction bold right parenthesis bold.
bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold 3 bold Cu to the power of bold 2 bold plus end exponent bold space bold plus bold space bold 6 bold e to the power of bold minus bold space bold space bold space bold rightwards arrow bold space bold space bold space bold 3 bold Cu bold left parenthesis bold s bold right parenthesis
bold therefore bold space bold space bold Cell bold space bold notation bold space bold is bold space bold Cr bold space bold vertical line bold space bold Cr to the power of bold 3 bold plus end exponent bold vertical line bold space bold vertical line bold vertical line bold space bold Cu to the power of bold 2 bold plus end exponent bold space bold vertical line bold space bold Cu