Page 209 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Electrolyte-definition, percentage of sulphuric acid and water effects of improper ratio of acid and water
on battery life

Electrolyte
A liquid substance that dissolves when an electric current flows through it is called an electrolyte. E.g. Sulfuric
acid, sodium chloride etc. Dilute sulfuric acid (H SO ) is used as the electrolyte for lead acid batteries. Specific
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gravity of pure sulfuric acid is 1.84. Dilution of this pure sulfuric acid is usually done by mixing one-part sulfuric acid
with seven parts distilled water to bring its specific gravity from 1.300 to 1.230. As per the battery manufacturer’s
recommendation if the battery cell contains P.V.C. 1.200 Vs if separators are used. Th. 1.230 Vs. Th. Use
electrolyte containing The electrolyte level in the battery cell should be 1/2” to 3/4” above the plates.
Percentage of sulphuric acid and water effects of improper ratio of acid and water on battery life -
The % sulfuric acid in a lead-acid battery electrolyte is around 37 - 38%. this concentration can do effect on the
battery’s performance.

High Acid Concentration: Too much sulfuric acid cause corrosion of the lead plates, battery life and potential
damage to the battery casing.
Low Acid Concentration: Insufficient sulfuric acid can reduce battery capacity and reduced ability of charge.

It is difficult to maintain acid-to-water ratio when adding electrolyte to a battery.
Batteries store electrical energy in chemical form. When the battery is fully charged, the positive plate, PbO, is
dark brown in color, while the negative plate, Pb, is gray in color and a spa of sulfuric acid, H,SO, (electrolyte).
Gravity ranges from 1.20 to 1.30. Each cell of a battery has a voltage of 2.2 volts. Thus is the whole battery
situation. Now when the current is taken from the battery, the sulfuric acid decomposes and H and SO ions are
separated from it. Of these, hydrogen (H ) is liberated to lead peroxide (PbO,) and is first converted into lead oxide
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(PbO), which, on mixing with sulfuric acid, is converted into lead sulphate (PbSO,). Water (H O) is produced in
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this process. The sulfate group (SO ) released during the decomposition of sulfuric acid is released from spongy
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lead (Pb) and is also converted into lead sulfate (PbSO,). Thus both the plates are converted into lead sulphate
(PbSO,) and appear white in color and as the water content increases in acid, the specific gravity of the acid
decreases.
Now when a current is sent through the cell to charge the battery, on the positive plate PbSO, SO, H O PbO,+
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2H,SO, and On the negative plate, PbSO, + H = Pb + H SO chemically reacts so that one plate becomes PbO,
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and the other Pb. The specific gravity of sulfuric acid increases due to the loss of water in the chemical process.
Specific gravity of water, acid and electrolyte. Temperature

effect on specific gravity. Battery troubles and their
remedies

Objectives: At the end of this lesson you shall be able to

• explain about specific gravity of water, acid and electrolyte
• demonstrate temperature effect on specific gravity
• demonstrate battery troubles and their remedies

Specific gravity of water, acid and electrolyte. Temperature effect on specific gravity
Specific gravity of water: The density of water is always considered to be 1. This makes it a standard for
comparing the density of other substances.
Specific gravity of acid: An acid is a substance in chemistry that either gives away a proton or accepts an
electron pair during reactions. Acids usually taste sour and can change the color of litmus paper to red. They’re
often grouped into strong or weak categories depending on how easily they break apart in water, releasing
hydrogen ions (H+). Examples include hydrochloric acid (HCl) and citric acid.

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CITS : Automotive - Mechanic Diesel - Lesson 57 - 61