CHEMISTRY REVUSUON QUESTIONS
CLASS 10
CLASS 10
1.
What is aqua regia?
Ans :
It is a mixture of conc. HCl and conc. HNO3 in the ratio of 3 : 1.
1
2.
A bud of petunia became reddish purple after first shower of rain. What does it indicate ?
Ans :
The rain was acid-rain.
2
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?
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
(c) 1 M NaOH pH = 14.0 (d) Tomato juice pH = 4.0
3
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
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
CaCO3 (s) + 2HCl → CaCl2 + H2O + CO2
3
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
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.
