In an alkaline battery, the anode (negative terminal) is made of zinc powder. This allows for a greater surface area which results in an increased rate of reaction and hence a greater rate of electron flow. The cathode (positive terminal) is composed of manganese dioxide. Alkaline batteries are comparable to zinc-carbon batteries, but the difference is that alkaline batteries use potassium hydroxide (KOH) as an electrolyte rather than ammonium chloride or zinc chloride.
They last approximately five times longer than a dry cell, pictured below and have an application in appliances which require intermittent bursts of high current such as a toy car.
The half-reactions are:
Zn (s) + 2OH-(aq) → ZnO (s) + H2O (l) + 2e−
2MnO2 (s) + H2O (l) + 2e− →Mn2O3 (s) + 2OH− (aq)
A dry cell is pictured on the right. Click to see the internal structure. The electrolyte is a paste made up of ammonium chloride and zinc chloride as opposed to potassium hydroxide, as is the case with an alkaline battery. When trying to recharge non-rechargeable battery, at least one of the oxidation-reduction reactions may not be reversible and at times the unwanted reactions take place to produce gas. This can be a dangerous situation.
At the anode (-) oxidation of the zinc case produces electrons according to the equation below
Zn(s) => Zn2+(aq) + 2e-
At the cathode (+) reduction of MnO2 occurs pretty much according according to the equation below.
A new cell produces about 1.5 volts, but this differs considerably as the battery is used. As the cell discharges products build up around the electrodes and can effectively cease the forward reaction. This occurs after prolonged use and the battery can recover if allowed to stand for a while to allow the products to diffuse away from the electrodes. For example ammonia gas can build up at the cathode and effectively insulate it from the electrolyte. After a while the gas diffuses away. Warming the cell increases the rate of diffusion and helps the cell recover quicker.
Apart from the difference in electrolyte how does the alkaline cell differ from the dry cell.
An alkaline battery uses zinc powder as the anode. This has the effect of
A battery left operating in a toy car for several weeks starts to break apart. Why?
What is the overall equation of a dry cell and an alkaline cell?
Why are dry cells prone to failure after long periods of use, even though they still have enough reactants for a longer period of usage?
Although dry cells can be made in very small sizes they are not used for watches and cameras rather mercury-zinc button cells are used. Why?
