Answer the following in brief. Write electrode reactions for the electrolysis of aqueous NaCl. - Chemistry

Advertisements
Advertisements
Answer in Brief

Answer the following in brief.

Write electrode reactions for the electrolysis of aqueous NaCl.

Advertisements

Solution

  • Reduction half-reaction at cathode:

At cathode, two reduction reactions compete.

i. Reduction of sodium ions.

`"Na"_(("aq"))^+ + "e"^(-) -> "Na"_("s"), "E"^circ = - 2.71 "V"`

ii. Reduction of water to hydrogen gas.

2H2O(l) + 2e- → H2(g) + `2"OH"_(("aq"))^-,` E° = - 0.83 V

The standard potential for the reduction of water is higher than that for the reduction of Na+. Hence, water has a much greater tendency to get reduced than the Na+ ion. Therefore, reduction of water is the cathode reaction when the aqueous NaCl is electrolysed.

  • Oxidation half-reaction at anode: 

At anode, there will be competition between oxidation of Cl ion to Cl2 gas as in the case of molten NaCl and the oxidation of water to O2 gas.

i. Oxidation of Cl- ions to chlorine gas

`2 "Cl"_(("aq"))^(-) -> "Cl"_(2("g")) + 2"e"^(-), "E"_"oxd"^circ` = - 1.36 V

ii. Oxidation of water to oxygen gas.

`2"H"_2"O"_(("l")) -> "O"_(2("g")) + 4"H"_(("aq"))^+ + 2 "e"^(-),  "E"_"oxd"^circ` = - 0.4 V

The standard electrode potential for the oxidation of water is greater than that of Cl ion or water has a greater tendency to undergo oxidation. Hence, an anode half-reaction would be oxidation of water. However, experiments have shown that the gas produced at the anode is Cl2 and not O2. This suggests that anode reaction is oxidation of Cl to Cl2 gas. This is because of overvoltage.

  • Net cell reaction:

The net cell reaction is the sum of two electrode reactions.

`2 "Cl"_(("aq"))^(-) -> "Cl"_(2("g")) + 2"e"^(-)`                     (Oxidation half reaction at anode)

`2"H"_2"O"_(("l")) + 2 "e"^(-) -> "H"_(2("g")) + 2"OH"_(("aq"))^-`    (Reductionhalfreactionat cathode)

_______________________________________________________________________________

`2 "Cl"_(("aq"))^(-) + 2"H"_2"O"_(("l")) -> "Cl"_(2("g")) + "H"_(2("g"))  + 2"OH"_(("aq"))^-`  (Overall cell reaction)

Concept: Electrolytic Cell
  Is there an error in this question or solution?
Chapter 5: Electrochemistry - Exercises [Page 118]

APPEARS IN

Balbharati Chemistry 12th Standard HSC for Maharashtra State Board
Chapter 5 Electrochemistry
Exercises | Q 3.03 | Page 118

RELATED QUESTIONS

Answer the following in one or two sentences.

Write the electrode reactions during electrolysis of molten KCl.


Answer the following in one or two sentences.

How many electrons would have a total charge of 1 coulomb?


Answer the following:

Explain electrolysis of molten NaCl.


Answer the following:

What current strength in amperes will be required to produce 2.4 g of Cu from CuSO4 solution in 1 hour? Molar mass of Cu = 63.5 g mol–1.


Answer the following:

How will you calculate the moles of electrons passed and mass of the substance produced during electrolysis of a salt solution using reaction stoichiometry?


Answer the following:

What are anode and cathode of H2 - O2 fuel cell? Name the electrolyte used in it. Write electrode reactions and net cell reaction taking place in the fuel cell.


When molten ionic compound is electrolyzed, a metal is formed at _______.


A cell constituted by two electrodes A (`"E"_("A"^+//"A")^0` = 0.35 V) and B (`"E"_("B"^+//"B")^0` = + 0.42 V) has value of `"E"_"cell"^0` equal to _________.


Name the process by which water produces hydrogen gas at cathode during electrolysis of aqueous NaCl.


Draw a well labelled diagram of a conductivity cell. Also write net cell reactions involved in electrolysis of aqueous NaCl.


Write a mathematical formula for mole ratio. How long will it take to produce 2.415g of Ag metal from its salt solution by passing a current of 3A? Molar mass of Ag= 107.9 g mol-1.


Explain construction, working in terms of cell reactions and the results of electrolysis of fused NaCl.


How many moles of electrons are required for reduction of 2 moles of Zn2+ to Zn? How many Faradays of electricity will be required?


How many moles of electrons are passed when 0.8 A current is passed for one hour through molten NaCl?


During the electrolysis of aqueous NaCl, the gas liberated at the cathode is ______.


How much coulomb is one faraday?


The standard electrode potential of electrode

\[\ce{\underset{(0.02M)}{Zn^2+ (aq)} || Zn(s)}\] is -0.76 V. Calculate its electrode potential.


Share
Notifications



      Forgot password?
Use app×