Bateries reasearch task

Madhu Edirisinghege

25/02/11

B) Evaluate the DRY CELL in comparison to a SILVER BUTTON CELL in terms of chemistry, cost and practicality, impact on society and environmental impact.

The dry cell and silver button cell are two types of cells that used widely throughout society. These cells differ in there chemistry, cost/practicality, impact of society and impact on the environment.

The dry cell consists of a zinc outer casing which acts as the negative electrode. An aqueous paste of ammonium chloride, powdered carbon and manganese dioxide around the carbon cathode create the rest of the cell. At the negative terminal zinc is oxidised while, ammonium ions, manganese dioxide and water are reduced. The cell produced a voltage of 1.5V overall.

Oxidation: Zn → Zn2+ + 2e-

Reduction: ...

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Oxidation: Zn → Zn2+ + 2e-

Reduction: NH4+ + MnO2 + H2O + e- →Mn (OH)3 + NH3

The silver button cell has a steel case which is in contact with powdered silver oxide to form the cathode. While the steel case in contact with powdered zinc forms the anode. A paste of potassium hydroxide separates the two substances and acts as a porous medium. At the negative terminal the zinc oxides in an aqueous solution with hydroxide ions to form zinc oxide and water, whilst at the positive terminal silver oxide and water reduce to form silver solid and hydroxide ions. The cell has an overall voltage of 1.3V.

Oxidation: 2MnO2 (s) + H2O (l) + 2e− →Mn2O3 (s) + 2OH− (aq)

Reduction: Ag2O(s) + H2O(l) + 2e- → 2Ag(s) + 2OH-(aq)

In terms of chemistry both cells differ greatly from the reactant to size and shape. The dry cell however has a slightly higher voltage than the silver button cell.

Both cells have positives and negatives in relation to there cost and practicality. A positive aspect in both cells is that a voltage is maintained over a long period of time, a negative however is that in the dry cell this voltage is lower than in the button cell. The button cell can deliver high currents where as the dry cell can not. The dry cell is relatively in expensive where as the silver button cell is much more expensive due to the presence of silver. The cost of silver for the cell is significant, each cell can cost up to $20, the cost of a dry cell can be anywhere between $3 to $5. The button cell is relatively small in comparison to the button cell, the light weight and small size enable its use in delicate devices such as hearing aids and pacemakers in conjunction with its light weight its ability to deliver current over a long period of time also enables these uses. A disadvantage in both cells is that they can not be recharged.

Both cells have impact upon society. Both cells have enabled greater use of technology within society, however to varying degrees. The dry cell for instance enables the use of small, portable entertainment devices for greater enjoyment of society for example, portable radios. The button cell however also has this benefit, as well as enabling those with hearing difficulties and heart complications to continue enjoying life. That is due to the small size, non toxic nature and ability to supply and high, constant voltage over a long period of time the silver button cell it can be used in medical devices such as hearing aids and heart pacemakers.

The button cell and dry cell also have impact upon the environment. The dry cell contains acidic paste containing manganese which reacts with the zinc casing in order to produce a current. This means that there is a high chance of the cell leaking. Zinc is a heavy metal and manganese is corrosive, if the batteries are burned or are placed inland fill the metals can be released into the environment. In large quantities it can have detrimental effects. The zinc can enter water systems polluting underground water systems and surface water and air pollution if burned. It would also have an impact on society as the workers who are exposed to the heavy metal and corrosive substances are more susceptible to developing abnormalities which can be fatal, such as cancer. Similarly in the button cell silver has major impacts on aquatic life. If was found the high levels of silver can lead to decreased major organ functions and is particularly lethal to aquatic plant species. The button cell also contains the corrosive substance potassium hydroxide which also causes abnormalities in organisms in high concentrations.

In comparing the two cells in cost and practicality, impact on society and environmental impact, the silver cell has some important advantages over the dry cell. The silver button cell has much longer life than the dry cell. That is it can deliver a consistently higher voltage over a greater period of time, this is especially important in medical devices. The silver button cell is also less likely to leak thus less chance of having detrimental effects on the environment. Overall the silver button cell has the properties of the dry cell and other features which enables its use in a diverse range of situations.

BATTERIES RESEARCH

Labelled diagram of the DRY CELL (include anode, cathode, reactions at the anode & cathode, electrolytes and voltage)

BIBLIOGRAPHY

Books

Roebuck, C. M.. "Production of Materials." Excel HSC chemistry . Glebe, N.S.W.: Pascal Press, 2000. 34-51.
Stamell, Jim. "The Production of Materials." Excel HSC chemistry . Glebe, N.S.W.: Pascal Press, 2008. 40-57.
Gribben, Peter. Excel HSC chemistry pocket book years 11-12 . Glebe, N.S.W.: Pascal Press, 2001. Print.
Smith, Roland. "Nuclear Chemistry." Conquering Chemistry. 3 ed. Sydney: McGraw-Hill Book Company Australia Pty Limited, 2000. 67- 84. Print.
Schell, Marilyn, and Margeret Hogan. "Production of Materials." Dot Point HSC Chemistry. Sydney: Science Press, 2007. 39-43. Print.
Carson, Peter, David Heffernan, and Peter Loucopoulos. "Production of Materials." Spotlight Chemistry HSC. Sydney: Science Press, 2005. 56-66. Print.

Internet

Silver - Ag - Chemical properties, Health and environmental effects." Water Treatment and Purification - Lenntech. N.p., n.d. Web. 27 Feb. 2011. <http://www.lenntech.com/periodic/elements/ag.htm>.

"Battery Chemistry Tutorial and FAQ from PowerStream: Custom battery chargers and power supplies for OEMs." PowerStream Power Supplies and Chargers for OEMs in a Hurry. N.p., n.d. Web. 23 Feb. 2011. <http://www.powerstream.com/BatteryFAQ.html>.

"Dry-Cell Batteries - WDNR." Welcome to the Wisconsin Department of Natural Resources website.... N.p., n.d. Web. 27 Feb. 2011. <http://dnr.wi.gov/org/aw/wm/recycle/newpages/drycellbattery.htm>.