Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) +...
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Transcript of Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) +...
![Page 1: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/1.jpg)
Dry cells
![Page 2: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/2.jpg)
Simple chemical cell
Zinc
![Page 3: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/3.jpg)
Simple chemical cell
Overall equation (Redox reaction):
Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s) Ionic equation:
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) Half equations:
Zn(s) Zn2+(aq) + 2e- Oxidation
Cu2+(aq) + 2e- Cu(s) Reduction
![Page 4: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/4.jpg)
Daniell cell
![Page 5: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/5.jpg)
Daniell cell Anode (oxidation / -ve ele
ctrode):Zn(s) Zn2+(aq) + 2e-
Cathode (reduction / +ve electrode):Cu2+(aq) + 2e- Cu(s)
Overall cell equation (Redox reaction):Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)
![Page 6: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/6.jpg)
Daniell cell
Disadvantages Liquid electrolyte may spill out inconvenient
to be used Require porous pot for separation of two
different electrolytes Low voltage ~ 1.1V
![Page 7: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/7.jpg)
Dry cell
Use a paste of electrolyte instead of aqueous electrolyte. Zinc-carbon cell Alkaline manganese cell Silver oxide cell / Button cell Nickel-cadmium cell (rechargeable)
![Page 8: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/8.jpg)
Zinc-carbon cell
![Page 9: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/9.jpg)
Zinc-carbon cell
Anode (oxidation / -ve electrode): zinc Cathode (reduction / +ve electrode): carbo
n Electrolyte: moist paste of ammonium chlo
ride Oxidizing agent: manganese(IV) oxide Additive: carbon powder is added to increa
se the conductivity
![Page 10: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/10.jpg)
Zinc-carbon cell
Anode (oxidation / -ve electrode):
Zn(s) Zn2+(aq) + 2e- Cathode (reduction / +ve electrode):
2NH4+(aq) + 2e– 2NH3(aq) + H2(g)
Hydrogen accumulates at electrode and decreases the current of the cell. This problem is solved by manganese(IV) oxide, an oxidizing agent that removes the hydrogen.
2MnO2(s) + H2(g) Mn2O3(s) + H2O()
![Page 11: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/11.jpg)
Zinc-carbon cell
Ammonia is taken up by zinc ions.Zn2+(aq) + 2NH3(aq) + 2Cl–(aq) Zn(NH3)2Cl2(s)
Overall cell equation:2MnO2(s) + 2NH4Cl(aq) + Zn(s) Zn(NH3)2Cl2(s) + H2O() + Mn2O3(s)
The overall voltage of this cell is 1.5 volts.
![Page 12: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/12.jpg)
Zinc-carbon cell
Disadvantages If current is drawn from the cell rapidly, the gaseous
product cannot be removed fast enough. The voltage drops as a result. It is restored after standing.
The lifetime of the cell is relatively short. There is a slow direct reaction between the zinc electrode and ammonium ions. After some time, the zinc case becomes thinner and the paste leaks out. The leakage problem can be solved by enclosing the whole cell in a steel or plastic case.
![Page 13: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/13.jpg)
Alkaline manganese cell
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Alkaline manganese cell
Anode (oxidation / -ve electrode): zinc powder
Cathode (reduction / +ve electrode): manganese(IV) oxide
Electrolyte: potassium hydroxide
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Alkaline manganese cell
Anode (oxidation / -ve electrode):Zn(s) + 2OH–(aq) ZnO(s) + H2O(l) + 2e–
Cathode (reduction / +ve electrode):2MnO2(s) + H2O(l) + 2e– Mn2O3(s) + 2OH–(aq)
The overall cell reaction is:Zn(s) + 2MnO2(s) ZnO(s) + Mn2O3(s)
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Alkaline manganese cell
Its lifetime is longer than that of a zinc-carbon cell. The outer steel case is not involved in the
reaction. Therefore, this cell does not leak. It is used when larger currents are needed,
for example in motorized toys. It is much more expensive than a zinc-
carbon cell. It gives 1.5 V.
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Silver oxide cell
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Silver oxide cell
Anode (oxidation / -ve electrode): zinc powder
Cathode (reduction / +ve electrode): silver oxide
Electrolyte: potassium hydroxide
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Silver oxide cell
Anode (oxidation / -ve electrode):Zn(s) + 2OH–(aq) ZnO(s) + H2O(l) + 2e–
Cathode (reduction / +ve electrode):Ag2O(s) + H2O(l) + 2e– 2Ag(s) + 2OH–(aq)
The overall cell reaction is:
Zn(s) + Ag2O(s) ZnO(s) + 2Ag(s)
![Page 20: Dry cells. Simple chemical cell Zinc Simple chemical cell Overall equation (Redox reaction): Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) Ionic equation:](https://reader035.fdocuments.net/reader035/viewer/2022062320/56649d8e5503460f94a77400/html5/thumbnails/20.jpg)
Silver oxide cell
The silver oxide cell is small. It lasts for a long time. It also gives a steady current. It is more expensive than other types of dry
cell. It gives 1.5 V.
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Nickel-cadmium cell (Ni-Cd)
Anode (oxidation / -ve electrode): cadmium
Cathode (reduction / +ve electrode): nickel(IV) oxide
Electrolyte: potassium hydroxide
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Nickel-cadmium cell (Ni-Cd)
It is classified as a secondary cell (rechargeable cell).
It gives a larger current. It is more expensive. It gives 1.25 volts. When the cell is recharged, an electric
current is passed through it in the direction opposite to that of the cell reaction.
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Pollution problems
Cells contain toxic materials. mercury in zinc-carbon cell cadmium in nickel-cadmium cell
Materials inside the cells do not decompose even after a long time.