Key Points - 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 of Acids:
(i) Mineral Acids: These are acids prepared from minrals present in the earth’s crust.
(ii) Organic Acids: These are acids produced by plants and animals (exception, hydrochloric acid).
(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. Acid + Base -  Salt + Water . Example: HCl + NaOH -  NaCl + H 2O

Neutralisation in Everyday Life:
(i)  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 of an acid, a base or a neutral solution.
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Classificaiton of Indicators:
Natural Indicators:
(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 Indicators:
(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.