B. Statements given below are incorrect. Write
the correct statements.
1. Chemical formula of aluminium sulphate is
Al(SO)
2. When magnesium is placed in contact with
oxygen, it forms magnesium hydroxide.
3. The substance/substances which take part
in a chemical reaction is are known as
active substance/substances.
4. When a chemical equation is made concise
by using symbols and formulae, then it is
called balanced equation.
5. When wood burns in air, then this reaction
is violated the law of conservation of mass.
Answers
Answer:
Q 1.
Why should magnesium ribbon be cleaned before burning in air?
SOLUTION:
Ans : Magnesium ribbon is cleaned before burning so that coating of impurity (such as oxide) formed on its surface is removed and it becomes pure magnesium.
Q 2.
Write the balanced equations for the following chemical reactions.
(a) Hydrogen + chlorine → hydrogen chloride
(b) Barium chloride + aluminium sulphate → barium sulphate + aluminium chloride
(c) Sodium + water → sodium hydroxide + hydrogen
SOLUTION:
Ans :
Q 3.
Write a balanced chemical equation with state symbols for the following reactions :
(a) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(b) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water
SOLUTION:
Ans :
Q 4.
A solution of the substance X is used for white washing.
(i) Name the substance X and write its formula.
(ii) Write the reaction of the substance X with water.
SOLUTION:
Ans : (i) The substance X is calcium oxide (also called quick lime). Its formula is CaO.
(ii)
Q 5.
Why is double the amount of gas collected in one of the test tubes in electrolysis of water than the amount collected in the other? Name the gas.
SOLUTION:
Ans : On electrolysis, water decomposes according to the reaction,
Thus, water decomposes to give hydrogen and oxygen in the ratio 2 : 1 by volume. The double volume of the gas collected is hydrogen.
Q 6.
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
SOLUTION:
Ans : The reaction between copper(II) sulphate and iron is represented as
In this displacement reaction, a more active element iron displaces another less reactive element from its compound copper(II) sulphate. The brown copper metal gets deposited on the iron nails. The colour of the solution changes from blue to light green due to the formation of Fe2+ ions.
Q 7.
Give an example of a double displacement reaction.
SOLUTION:
Ans : In the reaction of silver nitrate and sodium chloride, the silver exchanges its nitrate ions with chloride ions of sodium chloride and forms a precipitate of silver chloride. The chemical reaction is
Q 8.
Identify the substances that are oxidized and the substances that are reduced in the following reactions :
(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
SOLUTION:
Ans :
Q 9.
Which of the statements about the reaction below are incorrect?
(i) Lead is getting reduced.
(ii) Carbon dioxide is getting oxidised.
(iii) Carbon is getting oxidised.
(iv) Lead oxide is getting reduced.
A. (i) and (ii)
B. (i) and (iii)
C. (i), (ii) and (iii)
D. all of these
SOLUTION:
Ans : (A)
Q 10.
Fe2 O 3 + 2Al → Al 2 O 3 + 2Fe The above reaction is an example of a
A. combination reaction
B. double displacement reaction
C. decomposition reaction
D. displacement reaction
SOLUTION:
Ans : (D) It is an example of displacement reaction.Fe of Fe2O3 has been displaced by Al.
the chemical formula of aluminum sulphate is Al2(SO4) 3