When a silvery grey powder of a solid (A) is mixed with a powder of solid (B) no reaction occurs. But if the mixture is ignited and lighted using magnesium ribbon a reaction occurs with the evolution of a large amount of heat forming product (C) which settles down as liquid metal and the solid product (D) formed floats on the liquid (C). (C) in solid form reacts with moisture to form rust. The amount of heat generated during the reaction is so high that the reaction is used in welding of electric conductors, joints in railway tracks. Based on this information, answer any four questions from (a) to (e).
(a) Identify A and C?
(i) A – Al and C – Fe
(ii) A – Fe and C – Al
(iii) A – Mg and C- Al
(iv) A – Al and C - Cu
Answer
The reaction of a mixture of A and B in the presence of magnesium ribbon to form a liquid metal and oxide of D is the thermite reaction.
According to this, A is Al because it is a grey colored metal and C is Fe because it forms rust in the presence of air and moisture.
So, the correct answer is (i) A - Al and C - Fe
(b) Identify B and D which are oxides of:
(i) B – Fe, D – Al
(ii) B – Mg, D – Al
(iii) B – Al D - Cu
(iv) B – Al D – Fe
Answer
From the equation of thermite reaction,
B is an oxide of Fe , and D of Aluminum .
The correct answer is (i)
(c) Amphoteric oxides are:
(i) Metal oxides which do not react with acids but react with bases.
(ii) Metal oxides which react with both acids as well as bases.
(iii) Metal oxides which react with acids but do not react with bases.
(iv) Metal oxides which show no reaction with either acids or bases.
Answer
Ambhi means both. Therefore, the metal oxides which are able to react with both acid and base to form salt and water are known as amphoteric oxides.
So, the correct answer is (ii) Metal oxides which react with both acids as well as bases.
(d) Which of the following is amphoteric in nature:
(i) Both aluminium oxide and zinc oxide
(ii) Only zinc oxide
(iii) Only aluminium oxide
(iv) Neither of them.
Answer
Both aluminium oxide and zinc oxide are amphoteric in nature. Their reaction with acids and bases is given below:
Aluminium Oxide Acting as a Basic Oxide
Aluminium Oxide Acting as an Acidic Oxide
Similarly, ZnO is also an amphoteric oxide.
Zinc Oxide Acting as a Basic Oxide
Zinc Oxide Acting as an Acidic Oxide
So, the correct answer is (i)
(e) The reaction in which heat is generated is called as:
(i) Exothermic reaction
(ii) Endothermic reaction
(iii) Decomposition reaction
(iv) Precipitation reaction
Answer
Exo means out and thermic means heat . Hence, the reactions in which heat is generated are known as exothermic reactions .
So, the correct answer is (i) Exothermic reaction
