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Grade: 12
        














1.      Exactly 0.200 mole electrons is passed through two electrolytic cells in series. One contains silver ion, and the other, zinc  ion .assume that the only cathode reaction in each cell is the reduction  of the ion to the metal. How many grams of each metal will be deposited? (at. Mass of zn = 65, ag = 108)


a.       108g ag and 65 g zn.


b.      108 ag and 32.5g zn.


c.       21.6 ag and 6.5 g zn.


d.      21.6 g ag and 13 g zn.


 


2.       A steady current of 30.0A for 70.2 min corresponds to a passage of                                                  a.   1.2610^5  electrons.


 b.  1.26×10^5 f.


 c.  1.31 f.


 d.  1.31 c.


 


3.   Cu+ is not stable and undergoes disproportion. E for cu+ disproportionation.


(E°  cu2+/cu =0.153V , E°  cu+/cu=0.53V).


 


 

10 years ago

Answers : (4)

AskiitianExpert Shine
10 Points
							

Hi

Ans 1:

For silver , the conversion is Ag+ + e- -> Ag

Therefore 1 mole of electrons are reqd to make 1 mole i.e 108 gm of silver. hence .2 moles of electron will make .2x108 = 21.6 gm of silver.

 

For zinc, the connversion is Zn2+ + 2e- -> Zn

Therefore 2 moles of elctrons are reqd to make 1 mole i.e 65 gm of zinc, hence .2 mole electrons shall make .2x65/2 = 6.5 gm of zinc.

10 years ago
AskiitianExpert Shine
10 Points
							

Hi

Ans 2:

For a steady flow, the current I in amperes can be calculated with the following equation:

I = {Q \over t}

where

Q is the electric charge in coulombs transferred
t is the time in seconds

More generally, electric current can be represented as the time rate of change of charge, or

I = \frac{dQ}{dt}.

therefore, Q= 30 A x 70.2 x 60 sec = 126360 coulombs

1 faraday = 96 485.3415 coulombs

 

Therefore answer is 126360/96485.3415 = 1.31 faraday

10 years ago
AskiitianExpert Shine
10 Points
							

Hi

Please repost the third question, the question is not clear.

10 years ago
Ramesh V
70 Points
							

1)       for silver deposition :       Ag+     +     e-             ------>   Ag

                                                                     1 mole                   1 mole

         so , 0.2 moles of Ag is deposited i.e., 0.2*108 = 21.6 grams

        

        for zinc deposition :   Zn2+     +   2e-                ------>    Zn

                                                              2 mole                       1 mole

        so , 0.1 moles of Zn is deposited i.e., 0.1*65 =  6.5 grams

        So option is C

 

2)   Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes

     so Q = i*t

       Q=30*70.2*60

     Q = 126360 Coulombs

    but 1 faraday = 96485 Coulombs

    So its Q = 1.31 faraday

    So option is C

 

 

3) I want to make a small correction to question reg. elecric potential of  cu2+/cu+ ( taken frm standard books )

Its cu2+/cu+ =0.153V  i.e.,                     cu2+ + e-   ------>  cu           E0 = 0.153 V

Now going into problem:  Cu+ solutions, tend to give a disproportion reaction:

                                                       2Cu+ ----- >   Cu + Cu2+

                      
                     cu+ + e-    ------>  cu                                E0 = 0.53 V        so,  nE0 = 0.53 V   

                     cu+            ------>  cu2+ + e-               E0 = - 0.153 V       so,   nE0 = - 0.153 V

on adding above rxns we get  
 2Cu+ ----- >   Cu + Cu2+                  with  E0 = +0.377 V  

10 years ago
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