Question
Explain Daniell cell with diagram and explain different condition when external potential is applied in opposite direction.
✓
Answer
→ Daniell cell is a voltaic cell in which chemical energy convert into electrical energy.
→ In Daniell cell Zn metal rod act as anode and Cu metal rod act as cathode.
→ In Daniell cell the following reaction occurs.
$
Zn ( s )+ Cu ^{+2}( aq ) \rightarrow Zn ^{+2}( aq )+ Cu ( s )
$
→ When concentration for $Cu ^{+2}$ and $Zn ^{+2}$ ion is unit $(1 M )$ then cell potential of this cell is 1.1 V
→ such a device is called galvanic or a voltaic cell.
(1) Condition - a $\left( E _{\text {ext }}<1.1 V\right)$
→ If an external opposite potential is applied and increased slowly, we find that the reaction continues to take place till the opposing voltage reaches the value 1.1V
When $E _{ ext }<1.1 V$
(i) Electrons flow from the Zn rod to the Cu rod hence current flows from the Cu to Zn.
(ii) Zinc dissolves at anode and copper deposits at cathode.
(2) Condition - b $($ Eext $=1.1 V)$
→ The reaction stops altogether and no current flows through the cell.
When $E _{\text {ext }}=1.1 V$
(i) No flow of electrons or current
(ii) No chemical reaction observed.
(3) Condition - c (Eext > 1.1V)
→ Any further increase in the external potential again starts the reaction but in the opposite direction.
→The cell now functions as an electrolytic cell, a device for using electrical energy to carry non- spontaneous chemical reactions.
When $E _{ ext }>1.1 V$
(i) Electrons flow from Cu to Zn, and current flows from Zn to Cu.
(ii) Zinc is deposited at the zinc electrode and copper dissolves at copper electrode.
→ In Daniell cell Zn metal rod act as anode and Cu metal rod act as cathode.
→ In Daniell cell the following reaction occurs.
$
Zn ( s )+ Cu ^{+2}( aq ) \rightarrow Zn ^{+2}( aq )+ Cu ( s )
$
→ When concentration for $Cu ^{+2}$ and $Zn ^{+2}$ ion is unit $(1 M )$ then cell potential of this cell is 1.1 V
→ such a device is called galvanic or a voltaic cell.
(1) Condition - a $\left( E _{\text {ext }}<1.1 V\right)$
→ If an external opposite potential is applied and increased slowly, we find that the reaction continues to take place till the opposing voltage reaches the value 1.1V
When $E _{ ext }<1.1 V$
(i) Electrons flow from the Zn rod to the Cu rod hence current flows from the Cu to Zn.
(ii) Zinc dissolves at anode and copper deposits at cathode.
(2) Condition - b $($ Eext $=1.1 V)$
→ The reaction stops altogether and no current flows through the cell.
When $E _{\text {ext }}=1.1 V$
(i) No flow of electrons or current
(ii) No chemical reaction observed.
(3) Condition - c (Eext > 1.1V)
→ Any further increase in the external potential again starts the reaction but in the opposite direction.
→The cell now functions as an electrolytic cell, a device for using electrical energy to carry non- spontaneous chemical reactions.
When $E _{ ext }>1.1 V$
(i) Electrons flow from Cu to Zn, and current flows from Zn to Cu.
(ii) Zinc is deposited at the zinc electrode and copper dissolves at copper electrode.
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iii.What care is generally taken during intravenous injections and why?
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ii. The preservation of meat by salting and of fruits by adding sugar protects against bacterial action. How?
iii. Why the direction of osmosis gets reversed if a pressure larger than the osmotic pressure is applied to the solution side? Write its one application.
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iii.What care is generally taken during intravenous injections and why?
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Aariv Sharma is very fond of a special drink made by his grandmother using different fruits available in their hometown. It has an outstanding taste and also provide great health benefits of natural fruits. He thought of utilizing his grandmother recipe to create a new product in the beverage market that provide health benefits and also contain fizziness of various soft drinks available in the market.
i. How he can add fizz to the special drink made by his grandmother? (1)
ii. What is the law stated in the chapter that can help Aariv to make his drink fizzy? (1)
iii. What precautions he should take while bottling so that his product does not lose fizz during storage and handling across long distances? (2)