Page 31 - Curriculum Visions Dynamic Book

 A secondary battery works by converting chemical
energy to electrical energy. For this to happen there
have to be two different materials as electrodes, and an electrode: a conductor that forms one terminal of a cell. electron-carrying liquid, an electrolyte. The condition of
the electrolyte changes as it charges and discharges.
acidity: a general term for the strength of an acid in a solution.
electrolyte: a solution that conducts electricity.
Negative electrode made of lead
 The battery is fully charged. The negative electrode is formed
of spongy lead, and
the positive electrode
is lead dioxide. The concentration of sulphuric acid is at a maximum.
ion: an atom, or group of atoms, that has gained or lost one Sulphuric acid or more electrons and so developed an electrical charge.
electrolyte Ions carry electrical current through solutions.
Positive electrode made of lead dioxide
 The battery is being discharged through use. The two electrode materials begin to be converted to lead sulphate. The concentration of sulphuric acid is decreasing.
Lead sulphate is deposited on both electrodes.
Measuring the charge of a battery by its sulphuric acid concentration
As the cell gives out its electricity, the sulphuric acid is used up and becomes more dilute. This means that the state
of charge of a battery can be measured by its acid concentration using a hydrometer.
 To use a hydrometer, the acid is drawn up the syringe by squeezing and then releasing the rubber bulb. The float inside the hydrometer is marked with coloured bands. The higher the float rises, the more concentrated the acid, the greater the acid density, the better the battery charge. Floats that sink low in the hydrometer show a weak (low density) electrolyte, and thus a dilute acid. This means that the battery is discharged.
A cell
Hydrometer Car battery
 The battery is fully discharged. The electrodes are now covered with lead sulphate and the sulphuric acid concentration is very low. (Charging the battery using a generator will return the battery to the state in .)
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