Page 48 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

ii. Our stomach produces hydrochloric acid that helps in digestion of food. Sometimes

acid is secreted in large amount that causes indigestion. To get relief, we take an ant-
acid, such as milk of magnesia (magnesium hydroxide), a base , that neutralizes the

effect of excess acid.
iii. If the soil is too acidic, farmers treat it with a base such as slaked (calcium hydroxide)
that neutralises the excess of acid.

If the soil becomes too basic, farmers treat it with organic matter, such as compost or
manure.

iv. The waste from the factories is mostly acidic. So, it should be treated by adding bases
before releasing them directly into the water bodies.

v Salts are ionic compounds that are formed when an acid reacts with a base. They are usually
soluble in water. For example, NaCl (sodium chloride).

v In solid form, salts have high melting points. Their aqueous solutions are good conductors
of electricity.
v Salts are of three types–neutral, acidic and basic.

v Neutral salts are formed by the neutralisation reaction between strong acids and strong
bases. for example, NaCl (sodium chloride).

v Acidic salts are formed by the reaction of a strong acid with a weak base. For example,
NH Cl (ammonium chloride).
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v The reaction of a strong base with a weak acid results in the formation of a basic salt. For
example, Na CO (sodium carbonate).
2 3
v Salts are basically solid at room temperature. They can be white solids or of some other
colour.
v In 1766, Henry Cavendish conducted an experiment that involved a metal and he poured

acid on it. A gas was produced, which he called ‘inflammable gas’, which is now known as
hydrogen. Not only did he discover hydrogen, he also experimented how hydrogen reacted

with air. Cavendish also successfully made ‘fixed air’ or carbon dioxide as it is now known by
dissolving alkalis in acids.

Exercise

A. Tick (3) the correct answer.

1. Which of the following forms is a cation?
(a) Hydrogen (b) Copper (c) Magnesium (d) All of these

Ans. (d)
2. A .................... feels slippery to touch.

(a) Acid (b) Base (c) Salt (d) All of these
Ans (b)

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