CBSE Class 10 Science 2018 · Paper 31(B) · Question 17(b)

Metals and Non-metals 5 marks Medium

(1)A non-metal ‘P’ which is the largest constituent of air, when heated with hydrogen in $1 : 3$ ratio in the presence of catalyst (Fe) gives a gas Q.
(2)On heating P with oxygen an oxide R is formed.
(3)If this oxide (R) is passed into water in the presence of air, an acid S is formed which acts as a strong oxidizing agent. (a) Identify P, Q, R and S, and give chemical equations of the reactions involved to justify your answer. (b) To which group and period of modern periodic table does this non-metal P belong ?

Answer

P is nitrogen, Q ammonia, R nitric oxide and S nitric acid; nitrogen is in group 15, period 2.

(a) P is nitrogen,

N_{2}

, the largest constituent of air. Q is ammonia,

NH_{3}

N_{2} + 3 H_{2} Fe, heat 2 NH_{3}

R is nitric oxide, NO:

N_{2} + O_{2} heat 2 NO

S is nitric acid,

HNO_{3}

, a strong oxidising agent: in air,

2 NO + O_{2} \to 2 NO_{2}

, and then

4 NO_{2} + O_{2} + 2 H_{2} O \to 4 HNO_{3}

(Nitrogen dioxide,

NO_{2}

, is also accepted for R.) (b) Nitrogen (atomic number

7

, electronic configuration

2, 5

) belongs to group

15

and period

2

of the modern periodic table.

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