Page 39 - NCERT Science Class 10 English Medium

n The strength of an acid or an alkali can be tested by using a scale called the pH
scale (0-14) which gives the measure of hydrogen ion concentration in a solution.

n A neutral solution has a pH of exactly 7, while an acidic solution has a pH less
than 7 and a basic solution a pH more than 7.
n Living beings carry out their metabolic activities within an optimal pH range.
n Mixing concentrated acids or bases with water is a highly exothermic process.
n Acids and bases neutralise each other to form corresponding salts and water.
n Water of crystallisation is the fixed number of water molecules present in one formula
unit of a salt.
n Salts have various uses in everyday life and in industries.

E X E R C I S E S

1. A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky.
The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a
given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount
HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
5. Write word equations and then balanced equations for the reaction taking
place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.
6. Compounds such as alcohols and glucose also contain hydrogen but are not
categorised as acids. Describe an Activity to prove it.
7. Why does distilled water not conduct electricity, whereas rain water does?

34 Science

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