ACIDS: • These are the substances which have sour in taste. • They turn blue litmus solution to red. • They give H ions in aqueous solution Examples of Acids : - HCl - Hydrochloric Acid BASES • These substances are bitter in taste. • They turn red litmus solution to blue. • They give OH ions in aqueous solution. Examples of Bases : - NaOH - Sodium Hydroxide KOH - Potassium Hydroxide Alkalis - These are the bases soluble in water. like - NaOH (sodium Hydroxide) INDICATORS There are the substance that changes their colour / smell in different types of substances. Types of Indicators l. Natural Indicators - Those indicators found in nature by trees called Natural Indicators Ex - Litmus, Turmeric 2. Synthetic Indicators - These are the chemical substance prepare in laboratories. Ex- Phenolphthalein, Methyl Orange 3. Olfactory indicators - These substances have different odour in acids and Bases. Ex - Onion, clove oil, Vanilla Essence. Indicators: Substances which change their colour/smell in different types of substances (like acids and bases). Types of Indicators: (i) Natural indicators (ii) Synthetic indicators (iii) Olfactory indicators (i) Natural indicators: Found in nature in plants. Examples: Litmus, red cabbage leaves extract, flowers of hydrangea plant, turmeric. (ii) Synthetic indicators: These are chemical substances. Examples: Methyl orange, phenolphthalein. (iii) Olfactory indicators: These substances have different odour in acid and bases.

1. ACIDS, BASES & SALTS
Class 7 | Science

2. ACIDS
Acids are sour in taste.
They change colour of blue
litmus paper into red.
Examples: Orange, Lemon, Curd

3. BASES
Bases are bitter in taste.
They change colour of red
litmus paper into blue.
Examples: Baking soda, Soaps

4. SALTS
Salts can be acidic, basic or
neutral.
When an acid reacts with a
base, salt and water are formed.
Example: Sodium Chloride

5. Indicators
Substances that are used to indicate whether a
substance is acid or base are known as indicators.
Natural
Indicator
• Turmeric
• Chine rose petals
• Litmus
Synthetic
Indicator
• Phenolphthalein
• Methyl orange

6. Turmeric (Natural Indicator)
Turmeric is of Yellow colour.
It is used to test the Basic
solution.
Indicator Colour in
Acid
Colour in
Base
Turmeric Yellow Red/pink

7. China Rose (Natural Indicator)
China rose is of Pink colour.
It is used to test both Acids
and Bases.
Indicator Colour in
Acid
Colour in
Base
China Rose Dark pink Green

8. Litmus(Natural Indicator)
Litmus is extracted from
Lichens. It comes in the form of
strips of two colours.
Indicator Colour in
Acid
Colour in
Base
Red Litmus Paper No change Blue
Blue Litmus Paper Red No change

9. Phenolphthalein (Synthetic Indicator)
Phenolphthalein is a colorless
compound. It is used to test the
Basic solution.
Indicator Colour in
Acid
Colour in
Base
Phenolphthalein Colourless Pink

10. Methyl Orange (Synthetic Indicator)
Phenolphthalein is an orange
colour substance. It is used to
test both acids and Bases.
Indicator Colour in
Acid
Colour in
Base
Methyl Orange Red Yellow