Board Paper of Class 12 2018 Chemistry - Solutions

(a) Fill in the blanks by choosing the appropriate word/words from those given in the brackets:
(square pyramidal, electrical, 74, 26, sp³d², sp³d, chemical, 68, 32, tetrahedral, yellow, white, iodoform, Lucas)
(i) A Galvanic cell converts _______ energy into ______ energy.
(ii) The percentage of unoccupied spaces in bcc and fcc arrangements are _______ and ________ respectively.
(iii) Propan-2-ol on reaction with iodine and sodium hydroxide gives ______ precipitate and the reaction is called ________test.
(iv) The geometry of XeOF₄ molecule is ________ and the hybridisation of xenon atom in the molecule is __________.

(b) Complete the following statements by selecting the correct alternative from the choices given:
(i) During the course of an S_N1 reaction, the intermediate species formed is:
(ii) Purification of aluminium by electrolytic refining is called:
(iii) An aqueous solution of urea freezes at −0·186°C, K_f for water = 1·86 K kg mol^–1, K_b for water = 0·512 K kg mol^–1. The boiling point of urea solution will be:
​(iv) In the dehydration of alcohols to alkenes by heating with concentrated sulphuric acid, the initiation step is:

(c) Match the following:
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(i)	Rate constant	(a)	Dialysis
(ii)	Biodegradable polymer	(b)	Glycine
(iii)	Zwitter ion	(c)	Arrhenius equation
(iv)	Purification of colloids	(d)	PHBV

(d) Answer the following questions:
(i) (1) Why does the density of transition elements increase from Titanium to Copper? (at. no. Ti = 22, Cu = 29)
​(ii) Identify the compounds A, B, C and D.
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(iii) Calculate the osmotic pressure of a solution prepared by dissolving 0·025g of K₂SO₄ in 2·0 litres of water at 25°C assuming that K₂SO₄ is completely dissociated. (mol. wt. of K₂SO₄ = 174 g mol^–1)

​(iv) What type of isomerism is shown by the following coordination compounds: VIEW SOLUTION

(i) Write the rate law expression for the reaction A + B + C → D + E , if the order of reaction is first, second and zero with respect to A, B and C, respectively.
(ii) How many times the rate of reaction will increase if the concentration of A, B and C are doubled in the equation given in (i) above?

OR

The rate of reaction becomes four times when the temperature changes from 293 K to 313 K. Calculate the energy of activation (E_a) of the reaction assuming that it does not change with temperature. (R = 8·314 J K^–1 mol^–1) VIEW SOLUTION

(a) How do antiseptics differ from disinfectants?

(b) State the role of the following chemicals in the food industry: VIEW SOLUTION

An aromatic organic compound [A] on heating with NH₃ and Cu₂O at high pressure gives [B]. The compound [B] on treatment with ice cold solution of NaNO₂ and HCl gives [C], which on heating with Cu/HCl gives compound [A] again. Identify the compounds [A], [B] and [C]. Write the name of the reaction for the conversion of [B] to [C]. VIEW SOLUTION

Write the names of the monomers for each of the following polymers:
(a) Bakelite
(b) Nylon – 2 – nylon – 6 VIEW SOLUTION

Name the purine bases and pyrimidine bases present in RNA and DNA. VIEW SOLUTION

How will you obtain the following? (Give balanced equation.)
(i) Picric acid from phenol.
(ii) Ethyl chloride from diethyl ether.

OR

How will you obtain the following? (Give balanced equation.)
(i) Anisole from phenol
(ii) Ethyl acetate from ethanol. VIEW SOLUTION

40% of a first order reaction is completed in 50 minutes. How much time will it take for the completion of 80% of this reaction? VIEW SOLUTION

The freezing point of a solution containing 5·85g of NaCl in 100g of water is −3·348°C. Calculate van’t Hoff factor ‘i’ for this solution. What will be the experimental molecular weight of NaCl?
(K_f for water = 1·86 K kg mol^–1, at. wt. Na = 23, Cl = 35·5)

OR

An aqueous solution containing 12·48g of barium chloride (BaCl₂) in 1000g of water, boils at 100·0832°C. Calculate the degree of dissociation of barium chloride. (K_b for water = 0·52 K kg mol^–1, at. wt. Ba = 137, Cl = 35·5) VIEW SOLUTION

Examine the defective crystal given below and answer the question that follows:
 

A+	B–	A+	B–	A+
B–		B–	A+	B–
A+	B–	A+		A+
B–	A+	B–	A+	B–

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State if the above defect is stoichiometric or non-stoichiometric. How does this defect affect the density of the crystal? Also, write the term used for this type of defect. VIEW SOLUTION

Give reason for each of the following:
(a) For ferric hydroxide sol the coagulating power of phosphate ion is more than chloride ion.
(b) Medicines are more effective in their colloidal form.
(c) Gelatin is added to ice creams. VIEW SOLUTION

(a) For the complex ion [Fe(CN)₆]^3–, state: (b) Write the IUPAC name of [Co(en)₂Cl₂]⁺ ion and draw the structures of its geometrical isomers. VIEW SOLUTION

Explain why:
(i) Mn²⁺ is more stable than Fe²⁺ towards oxidation to +3 state.

(At. no. of Mn = 25, Fe = 26)

(ii) Transition elements usually form coloured ions.

(iii) Zr and Hf exhibit similar properties.

(At. no. of Zr = 40, Hf = 72)

OR

Complete and balance the following chemical equations:
(i) KMnO₄ + KI + H₂SO₄ → _____ + ______ + ______ + _______
(ii) K₂Cr₂O₇ + H₂SO₄ + H₂S → _____ + ______ + ______ + _______
(iii) KMnO₄ + H₂SO₄ + FeSO₄ → _____ + ______ + ______ + _______ VIEW SOLUTION

(a) Arrange the following in the increasing order of their basic strength:

b) Give a balanced chemical equation to convert methyl cyanide to ethyl alcohol.

(c) What happens when benzene diazonium chloride reacts with phenol in weak alkaline medium? (Give balanced equation). VIEW SOLUTION

Name the sulphide ore of Copper. Describe how pure copper is extracted from this ore. VIEW SOLUTION

(i) Calculate the emf and Δ𝐺° for the cell reaction at 25°C:
Given E° Zn²⁺/Zn = –0·763 and E°Cd²⁺/Cd = –0·403V

(ii) Define the following terms:

OR

(i) The specific conductivity of a solution containing 5 g of anhydrous BaCl₂ (mol. wt. = 208) in 1000 cm³ of a solution is found to be 0·0058 ohm^–1cm^–1_. (ii) What is an electrochemical series? How is it useful in predicting whether a metal can liberate hydrogen from acid or not? VIEW SOLUTION

(i) Explain why:
(ii) Draw the structures of the following:

OR

(i) Explain why:
​(ii) Complete and balance the following reactions: VIEW SOLUTION

(i) Give balanced equations for the following reactions:
​(ii) Give one chemical test each to distinguish between the following pairs of compounds:

OR

(i) Write chemical equations to illustrate the following name reactions:
​(ii) Explain why: VIEW SOLUTION