Subject

Chemistry

Class

CBSE Class 12

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Sample Papers

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 Multiple Choice QuestionsLong Answer Type

31.

(a) Define the following terms:

(i) Ideal solution

(ii) Azeotrope

(iii) Osmotic pressure

(b) A solution of glucose (C6H12O6) in water is labeled as 10% by weight. What would be the molality of the solution?

(Molar mass of glucose = 180 g mol-1)

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32.

(a) Give reasons for the following:

(i) Mn3+ is a good oxidising agent.

(ii)   Values are not regular for first row transition metals (3d series).

(iii) Although ‘F’ is more electronegative than ‘O’, the highest Mn fluoride is MnF4, whereas the highest oxide is Mn2O7.

(b) Complete the following equations:

 


(a) Outer electronic configuration f Mn is 3d5 4s2.

Outer electronic configuration of Mn3+ is 3d4 4s0.

Now Mn3+ is a strong oxidising agent. A good oxidizing agent reduces itself . i.e. gains electrons from other. Its tends to gain one more electron to acquire stable electronic configuration. If it gains one electron, its configuration will be 3d5, which is stable .this is the reason, it acts as a good reducing agent.

 

(ii)  Values are not regular which can be explained by the irregular variation of ionisation enthalpies i.e. iH1 + iH2 and also the sublimation enthalpies which are relatively much less for manganese and vanadium.

(iii) The ability of oxygen to stabilise the higher oxidation state exceeds that of fluorine. Also, the ability of oxygen to form multiple bonds with metals favours Mn2O7. Therefore, the highest Mn fluoride is MnF4 whereas highest oxide is Mn2O7. In Mn2O7, each Mn is tetrahedrally surrounded by O's including a Mn—O—Mn bridge.


b) 
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33.

(a) Why do transition elements show variable oxidation states?

(i) Name the element showing the maximum number of oxidation states among the first series of transition metals from Sc (Z = 21) to Zn (Z = 30).

(ii) Name the element which shows only +3 oxidation state.

(b) What is lanthanoid contraction? Name an important alloy which contains some of the lanthanoid metals.

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34.

(a) How will you convert the following? 

(i) Propanone to Propan-2-ol

(ii) Ethanal to 2-hydroxy propanoic acid

(iii) Toluene to benzoic acid


(b) Give simple chemical test to distinguish between:

(i) Pentan-2-one and Pentan-3-one

(ii) Ethanal and Propanal

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35.

(a) Write the products of the following reactions:

(b) Which acid of each pair shown here would you expect to be stronger?

(i) F — CH2 —COOH or Cl — CH2 — COOH

(ii) 

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