CHEMISTRY REVUSUON QUESTIONS
CLASS 10

1.

What is aqua regia?

Ans :

It is a mixture of conc. HCl and conc. HNO₃ in the ratio of 3 : 1.

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2.

A bud of petunia became reddish purple after first shower of rain. What does it indicate ?

Ans :

The rain was acid-rain.

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3.

Given below are the pH values of four different liquids :
7.0, 14.0, 4.0, 2.0
Which of these could be that of
(a) lemon juice,
(b) distilled water,
(c) 1 M sodium hydroxide solution,
(d) tomato juice?

Ans :

(a) Lemon juice pH = 2.0 (b) Distilled water pH = 7.0
(c) 1 M NaOH pH = 14.0 (d) Tomato juice pH = 4.0

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4.

Explain the action of dilute hydrochloric acid on the following with chemical equations:

(a) Magnesium ribbon (b) Sodium hydroxide (c) Crushed egg shells

Ans :

(a) Hydrogen gas will be formed, e.g.
Mg (s) + 2HCl (dil) → MgCl₂ (aq) + H₂ (s)
(b) Sodium chloride and water will be formed, e.g.
NaOH + HCl → NaCl + H₂O

(c) Crushed egg shells are made up of CaCO₃ which reacts with dil HCl to give brisk effervescence due to CO₂, e.g.
CaCO₃ (s) + 2HCl → CaCl₂ + H₂O + CO₂

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5.

On passing excess carbon dioxide gas through lime water, it first turns milky and then becomes colourless. Explain why? Write all the chemical equations of the reactions involved.

Ans :

Ca(OH)₂ + CO₂ → CaCO₃(s) + H₂O
CaCO₃(s) + CO₂(g) + H₂O(l) → Ca(HCO₃)₂

Lime water turns milky due to the formation of calcium carbonate. It becomes colourless when excess of CO₂ is passed due to formation of Ca(HCO₃)₂ which is soluble in water.