Tag: oxidation- reduction reactions

Quizzes (4) Questions (35)

Questions Related to oxidation- reduction reactions

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

The negative Zn pole of Daniel cell, sending a constant current through a circuit, decreases in mass by 0.13 g in 30 minutes. If the chemical equivalent of Zn and Cu and 32.5 and 31.5 respectively, the increase in the mass of the positive Cu pole in this time is : 

  1. 0.180 g

  2. 0.141 g

  3. 0.126 g

  4. 0.242 g
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Faraday's laws of electrolysis, the mass deposited is proportional to the chemical equivalent. The mass of Cu deposited = (Mass of Zn lost * Equivalent weight of Cu) / Equivalent weight of Zn = (0.13 * 31.5) / 32.5 = 0.126 g.

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

The passage of electricity in the Daniell cell when $Zn$ and $Cu$ electrodes are connected is from:

  1. $Cu$ to $Zn$ in the cell
  2. $Cu$ to $Zn$ outside the cell
  3. $Zn$ to $Cu$ outside the cell
  4. $Zn$ to $Cu$ in the cell
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In Daniell cell, Zn acts an anode and Cu acts as cathode, electron flow takes place from anode to cathode and hence, electricity flows from Cu to Zn outside the cell.

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

Daniel cell operates under nonstandard state conditions. If the equation of the cell reaction is multiplied by 2 then:

  1. $E$ and $E^o$ remain unchanged
  2. $E$ is doubled
  3. $n$ remains unchanged in Nernst equation
  4. $Q$ is halved in Nernst equation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nernst's equation states ${ E } _{ cell }={ E } _{ cell }^{ 0 }+\dfrac { RT }{ nF } ln\left[ { M }^{ + } \right] $

Where $E$ and ${ E }^{ 0 }$ of cell are independent of volume/quantity of reacting species in electrolyte, they are intunsic properties of cell. Hence, on doubling cell equation of Daniel cell.
$Zn\left| { Zn }^{ 2+ } \right| \left| { Cu }^{ 2+ } \right| Cu$,
its e.m.f $(E)$ and standard e.m.f $\left( { E }^{ 0 } \right) $ remain unchanged where ${ E }^{ 0 }$ stays at $1.09V$.

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

For the Daniel cell involving the cell reaction${ Zn } _{ (s) }+{ { Cu }^{ +2 } } _{ (aq) }\rightleftharpoons { { { Zn }^{ +2 } } } _{ (aq) }+{ Cu } _{ (s) }$ the standard free energies of formation of  ${ Zn } _{ (s) }$, ${ Cu } _{ (s) }$, ${ { Cu }^{ +2 } } _{ (aq) }$ and ${ { { Zn }^{ +2 } } } _{ (aq) }$ are 0, 0, 64.4 KJ/Mole and -154.0 KJ/Mole, respectively. Calculate the standard EMF of the cell?

  1. $2.13 Volts$
  2. $1.13 Volts$
  3. $2.26 Volts$
  4. $3.42 Volts$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\because \quad \Delta { G }^{ 0 }=\left( { G } _{ { Zn }^{ 2+ } }^{ 0 }-{ G } _{ { Cu }^{ 2+ } }^{ 0 } \right) $ $= (-154-64.4) KJ/Mole$

$\therefore(-2\times{E}^{0}\times F)$ $=(-218.4\times {10}^3)$
$\therefore E^0=1.1316\quad volt$

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

Which of the following statement is TRUE for the electrochemical Daniel cell :

  1. Electron flow from Zinc electrode to Copper electrode.

  2. Current flows from zinc electrode to copper electrode.

  3. Cation moves towards copper electrode.

  4. Cation moves towards zinc electrode.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

During reaction of $Zn\rightarrow{Zn}^{2+}+{2e}^{-}$ extra electron goes from anode to cathode or flow of $e^-$ from Zinc to Copper takes place and current flows from Copper to Zinc.