12. How do you count for the following observations?
(a) Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
(b) When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why?
Answer:
(a) While manufacturing benzoic acid from toluene, alcoholic potassium permanganate is used as an oxidant due to the given reasons.
(i) In a neutral medium,
We can see that the same compound is oxidized and reduced simultaneously in the reaction.
The reactions in which the same compound is oxidized and reduced is known as disproportionation reaction. Then, we can say that the alkaline decomposition of cyanogens is a disproportionation reaction.
21. The
22.Consider the elements:
Cs, Ne, I and F
(a) Identify the element that exhibits only negative oxidation.
(b) Identify the element that exhibits only positive oxidation.
(c) Identify the element that exhibits both negative and positive oxidation states.
(d) Identify the element that exhibits neither negative nor positive oxidation state?
Answer:
(a) F exhibits only negative oxidation no. That is -1.
(b) Cs exhibits only positive oxidation no. That is +1.
(c) I exhibits both negative and positive oxidation no. That is -1, +1, +3, +5 and +7.
(d) Ne exhibits neither negative nor positive oxidation no. That is 0.
23. Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.
Answer:
The redox reaction is as given below:
24. Refer to the periodic table given in your book and now answer the following questions:
(a) Select the possible non–metals that can show disproportionation reaction?
(b) Select three metals that show disproportionation reaction?
Answer:
One of the reacting elements always has an element that can exist in at least 3 oxidation numbers.
(i) The non–metals which can show disproportionation reactions are P, Cl and S.
(ii) The three metals which can show disproportionation reactions are Mn, Ga and Cu.
25. In Ostwald’s process for the manufacture of nitric acid, the first step involves the oxidation of ammonia gas by oxygen gas to give nitric oxide gas and steam. What is the maximum weight of nitric oxide that can be obtained starting only with 10.00 g. of ammonia and 20.00 g of oxygen?
Answer:
The balanced reaction is as given below:
28. Arrange the given metals in the order in which they displace each other from the solution of their salts.
Al, Fe, Cu, Zn, Mg
Answer:
A metal with stronger reducing power displaces another metal with weaker reducing power from its solution of salt.
The order of the increasing reducing power of the given metals is as given below:
Cu < Fe < Zn < Al < Mg
Therefore, Mg can displace Al from its salt solution, but Al cannot displace Mg. Thus, the order in which the given metals displace each other from the solution of their salts is as given below: Mg >Al>Zn> Fe >Cu
29. Given the standard electrode potentials,
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