Chapter - 5 Acids, Bases and Salts
There are three types of Substances: Acids, Bases and Indicators.
Acids: Acids are sour in taste.
They are corrosive in nature.
A concentrated acid cuts through clothes and eats away the wool.
If it falls on the skin. it can cause burns.
They are good conductors of electricity, as they allow the passage of electric current through
them.
Types ofAcids:
(i) Organic Acids: These are acids produced by plants and animals (exception hydrochloric acid)
(ii) Mineral Acids: These are acids prepared from minerals present in the earth's crust.
(iii) Weak Acids: These do not dissociate completely in solution. Example: nitric acid,
sulphuric acid.
(iv) Strong Acids: These dissociate completely in solution. Example: tartaric acid, lactic
acid.
Neutralization: it is the reaction between an acid and a base which results in formation of salt and water.
Neutralisation in Everyday Life:
Indigestion: Too much acid in stomach causes indigestion. It is neutralized by taking
an antacid like milk of magnesia.
(ii) Ant sting: When an ant bites, it injects formic acid into the skin. The effect is
neutralized by rubbing moist baking soda (sodium hydrogencarbonate) or calamine
(containing zinc carbonate).
(iii) Soil treatment: When the soil is too acidic, it is neutralized by treating with quicklime
(calcium oxide) or slaked lime (calcium hydroxide).
Acid turns blue litmus red. Bases turn red litmus blue.
Substances which are neither acidic nor basic are called neutral.
Solutions of substances that show different colour in acidic. basic and neutral solutions are
called indicators.
An acid and a base neutralise each other and form a salt. A salt may be acidic, basic or neutral In nature.
Bases: Bases are bitter in taste and soapy to touch.
Two types of Bases:
(i) Weak Bases: These naturally produce less hydroxide ions in solution. Example:
magnesium hydroxide, ammonium hydroxide.
(ii) Strong Bases: These produce more number of hydroxide ions on dissolving in water.
Example: caustic soda, caustic potash.
Indicators: it is special chemical that changes its colour to indicate the presence of a
chemical substance.
It is used to confirm the presence ofan acid, a base or a neutral solution.
Classificaiton of Indicators:
Natural lndicators:
(i) Litmus: it is extracted from lichens. It is available in the form of strips of paper or in
the form of a solution.
(ii) Turmeric: it remains yellow in neutral and acidic solutions but turns red in alkaline
solutions.
(iii) China rose: it turns acidic solutions to dark pink (magenta) and basic solution to
green.
(iv) Red cabbage: it turns acidic solutions to red and basic solutions to blue.
Other lndicators:
(i) Methyl Orange: it gives pinkish red colour with acidic solutions and yellow colour
with bases.
(ii) Phenolphthalein: it is an acid-base indicator. It is colourless in acidic solutions but
turns pink in alkali solutions.
class 7 science ch 4 acid base and salt
Class 7 science pdf notes
Chapter 1
Chapter 2
Chapter 3
Chapter 4 )
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chater 10
Chapter 11
Chapter 12
