Page 47 - Science Class 07

3. Name the acid found in lemon.
4. What happens when red litmus-paper is tested with base?

5. What do you mean by neutral substances?

Classification : Grouping substances on similar characteristics

Acidic substances : Substances which contain acid
Basic substances : Substances which react with acid to form salt and water
Neutral substances : Substances which are neither acidic nor basic in nature

Organic acids : All the naturally occurring weak acids
Inorganic acids : Strong acids prepared in laboratories
Alkalis : Water soluble bases

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i A substance is a sample of matter whose physical and chemical properties are the same
throughout the sample because the matter has a constant composition.
i The word acid is derived from the Latin world ‘Acidus’ which means sour.
i Sour taste of fruits and vegetables say that acid is present in them, e.g., lemon and oranges
contain citric acid hence, called citrus fruits.

i All the organic acids are of biological origin.
i Hydrochloric acid (HCl), Nitric acid (HNO ), Sulphuric acid (H SO ), Phosphoric acid and
3 2 4
(H PO ), etc. are inorganic or strong acids.
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i Indicators change their colours when added to a solution containing an acidic or a basic
substance.
i Bases are formed by burning of metals in the presence of oxygen.

i Some metallic oxides can be dissolved in water and form alkalis.
i The complete reaction of an acid with a base to form a salt and water is called neutralization.

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A. Tick (3) the correct op on.
1. Which of the following is not an acid-base indicator?
(a) Blue litmus (b) Methyl orange
(c) Phenolphthalein (d) Digene
2. Which of the following is a strong acid?
(a) Ni ric acid (b) Citric acid

(c) Ace c acid (d) Tartaric acid

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