Friday 31 August 2018

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.
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?
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
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
(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
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
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.

Monday 27 August 2018

Wednesday 15 August 2018