Question

The following takes place in a voltaic cell:
Zn(s) + Cu2+(1 M) → Cu(s) + Zn2+(1 M).
The cell has a voltage of +1.10 V.
Choose the answer that best relates to
questions 1-4.
(A) there is no change in the voltage
(B) the voltage becomes zero
(C) the voltage increases
(D) the voltage decreases, but stays
positive
(E) the voltage becomes negative
1. What happens to the voltage when a
saturated ZnSO4 solution is added to
the zinc compartment of the cell?
2. What happens to the cell voltage
when the copper electrode is made
smaller?
3. What happens to the cell voltage
when the salt bridge is filled with
deionized water instead of 1 M
KNO3?
4. What happens to the cell voltage
after the cell has operated for 10
minutes?

Could you please explain why?

Answer 1

1. What happens to the voltage when a saturated ZnSO4 solution is added to the zinc compartment of the cell?Answer: the voltage decreases, but stays positive.

2. What happens to the cell voltage when the copper electrode is made smaller? Answer: there is no change in the voltage

3. What happens to the cell voltage when the salt bridge is filled with deionized water instead of 1 M KNO3? Answer:  the voltage becomes zero
4. What happens to the cell voltage after the cell has operated for 10 minutes? Answer: the voltage decreases, but stays positive.

2) When the copper electrode is made smaller , the cell voltage will not change because size of the electrode doesn't affect voltage.Voltage depends on the chemical nature of the electrode not on the size.

3) in this cell, electrons are released by zinc (anode) and accepted by copper(cathode).Due to the movement of electrons charge get accumulated near the two electrodes which prevents further flow of electrons and hence voltage becomes zero.

Salt bridge maintains the charge balance.The electrons from anode move through the wire towards cathode, leaving unbalanced positive charge In order to maintain neutrality, the negatively charged ions in the salt bridge will migrate into the anodic half cell. Similarly, cathode accepts electrons and to maintain electroneutarlty positive charged ions of the salt bridge migrate into the cathodic half cell.

So, when the salt bridge is filledd with deionized water instead of KNO3 , the voltage will become zero because deionized water will not be able to maintain the electroneutarlty of the cell.

4) The cell voltage will decrease after the cell has operated for ten minutes because as the time passes more of the zinc will oxidizes to Zn2+ and more of the copper will get accumulated because of reduction of Cu2+. So, [Zn2+] concentration will increase and [Cu2+] decreases. [Zn2+]/[Cu2+] ratio increases and hence Ecell decreases. This will happen till the equilibrium is reached and then reaction will stop as Ecell becomes zero.