5.5 CHAPTER 5. THE CHEMICAL INDUSTRY
- A battery consists of one or more voltaic cells, each of which is madeup of two
half cells that are connected in series by a conductive electrolyte. Eachhalf cell
has a net electromotiveforce (emf) or voltage.The net voltage of the battery is
the difference betweenthe voltages of the half-cells. This potential difference
between the two half cells is what causes an electric current to flow. - A primary battery cannot be recharged, but a secondary battery can be recharged.
- The capacity of a battery depends on the chemical reactions in the cells, the
quantity of electrolyteand electrode material in the cell, and the discharge
conditions of the battery. - The relationship between the current, discharge time and capacity of abattery is
expressed by Peukert’s law:
Cp= Ikt
In the equation, ’Cp’ represents the battery’s capacity (Ah), I is the discharge
current (A), k is the Peukert constant and t is thetime of discharge (hours).
- Two common types ofbatteries are lead-acid batteries and the zinc-carbon dry
cell. - In a lead-acid battery, each cell consists of electrodes of lead (Pb) and lead (IV)
oxide (PbO 2 ) in an electrolyte of sulfuric acid (H 2 SO 4 ). When the battery dis-
charges, both electrodes turn into lead (II) sulphate (PbSO 4 ) and the electrolyte
loses sulfuric acid to become mostly water. - A zinc-carbon cell is made up of an outer zinc container, which acts as the anode.
The cathode is the central carbon rod, surrounded by a mixture of carbon and
manganese (IV) oxide (MnO 2 ). The electrolyte is a paste of ammonium chloride
(NH 4 Cl). A fibrous fabric separates the two electrodes, and a brass pin in the
centre of the cell conducts electricity to the outside circuit. - Despite their many advantages, batteries are made of potentially toxicmaterials
and can be damaging tothe environment.
Chapter 5 End of Chapter Exercises
- Give one word or term for each of the following descriptions:
(a) A solid organic compound that can be usedto produce liquid
fuels.
(b) The process used toconvert heavy hydrocarbons into light hydro-
carbons.
(c) The process of separating nitrogen from liquid air.
(d) The main raw material in the chloralkali industry.