XII – ISC Chemistry Paper 2018

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ISC Paper 2018

Chemistry

Maximum Marks: 70

Time allowed: 3 hours

  • Answer all questions in Part I and six questions from Part II, choosing two questions from Section A, two from Section B and two from Section C.
  • All working, including rough work, should be done on the same sheet as, and adjacent to, the rest of the answer.
  • The intended marks for questions or parts of questions are given in brackets [ ].
  • Balanced equations must be given wherever possible and diagrams where they are helpful.
  • When solving numerical problems, all essential working must be shown.
  • In working out problems use the following data:

Gas constant R = 1.987 cal deg-1 mol-1 = 8.314 JK-1 mol-1 = 0.0821 dm3 atm K-1 mol-1 . 1L atm = 1 dm3 atm = 101.3 J. 1 Faraday = 96500 Coulombs.

Avogadro’s number = 6.023 × 1023

Part – I (20 Marks)

Answer all questions.

Question 1.

(a) Fill in the blanks by choosing the appropriate word/words from those given in the brackets:

[4×1]

(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 ________.

Solution

 

Explanation: 

(b) Complete the following statements by selecting the correct alternative from the choices given: [4×1]

(i) During the course of an SN1 reaction, the intermediate species formed is:

(1) a carbocation

(2) a free radical

(3) a carbanion

(4) an intermediate complex

Solution

 

Explanation: 

(ii) Purification of aluminium by electrolytic refining is called:

(1) Serpeck’s process

(2) Hoope’s process

(3) Hall’s process

(4) Baeyer’s process

Solution

 

Explanation: 

(iii) An aqueous solution of urea freezes at – 0.186°C, Kf for water = 1.86 K kg mol–1, Kb for water = 0.512 K kg mol–1. The boiling point of urea solution will be:

(1) 373.065 K

(2) 373.186 K

(3) 373.512 K

(4) 373.0512 K

Solution

 

Explanation: 

(iv) In the dehydration of alcohols to alkenes by heating with concentrated sulphuric acid, the initiation step is:

(1) formation of carbocation

(2) formation of an ester

(3) protonation of alcohol molecule

(4) elimination of water

Solution

 

Explanation: 

(c) Match the following: [4×1]

(i) Rate constant                                                              (a) Dialysis

(ii) Biodegradable polymer                                            (b) Glycine

(iii) Zwitter ion                                                                  (c) Arrhenius equation

(iv) Purificaiton of colloids                                              (d) PHBV

Solution

 

Explanation: 

(d) Answer the following questions: [4×2]

(i)  (1) Why does the density of transition elements increase from Titanium to Copper? (at. no. Ti = 22, Cu = 29)

(2) Why is zinc not regarded as a transition element? (at. no. Zn = 30)

Solution

 

Explanation: 

(ii) Identify the compounds A, B, C and D.

{CH_3CN{\overset{H_2O/H^+}{\longrightarrow}} A {\overset{NH_3}{\longrightarrow}} B {\overset{heat}{\longrightarrow}} C {\overset{Br_2/KOH}{\longrightarrow}} D}

Solution

 

Explanation: 

(iii) Calculate the osmotic pressure of a solution prepared by dissolving 0.025 g 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)

Solution

 

Explanation: 

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

[PtCl2(NH3)4] Br2 and [Pt Br2 (NH3)4 ] Cl2

Write their IUPAC names.

Solution

 

Explanation: 

Question 2

(a)

(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?

Solution

 

Explanation: 

OR

(b) The rate of reaction becomes four times when the temperature changes from 293 K to 313 K. Calculate the energy of activation (Ea ) of the reaction assuming that it does not change with temperature.

(R = 8.314 J K–1 mol–1)

Solution

 

Explanation: 

Question 3

(a) How do antiseritics differ from disinfectants?

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

(i) Sodium benzoate

(ii) Aspartame

Solution

 

Explanation: 

Question 4

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].

Solution

 

Explanation: 

Question 5

Write the names of the monomers for each of the following polymers:

(a) Bakelite

(b) Nylon–2–nylon–6

Solution

 

Explanation: 

Question 6

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

Solution

 

Explanation: 

Question 7

(a) How will you obtain the following? (Give balanced equation.)

(i) Picric acid from phenol

(ii) Ethyl chloride from diethyl ether.

Solution

 

Explanation: 

OR

(b) How will you obtain the following? (Give balanced equation.)

(i) Anisole from phenol

(ii) Ethyl acetate from ethanol.

Solution

 

Explanation: 

Question 8

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?

Solution

 

Explanation: 

Question 9

(a) The freezing point of a solution containing 5.85 g of NaCL in 100 g of water is –3.348°C. Calculate van’t Hoff factor for this solution. What will be the experimental molecular weight of NaCL?

(Kf for water = 1.86 K kg mol–1, at wt, Na = 23, Cl = 35.5)

Solution

 

Explanation: 

OR

(b) An aqueous solution containing 12.48 g of barium chloride (BaCl2 ) in 1000g of water, boils at 100.0832°C. Calculate the degree of dissociation of barium chloride.

(Kb for water = 0.52 K kg mol–1, at. wt. Ba = 137, Cl = 35.5)

Solution

 

Explanation: 

Question 10

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

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.

Solution

 

Explanation: 

Question 11

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.

Solution

 

Explanation: 

Question 12

(a) For the complex ion [ Fe (CN)6]3- , state :

(i) the type of hybridisation

(ii) the magnetic behaviour

(iii) the oxidation number of the central metal atom

Solution

 

Explanation: 

(b) Write the IUPAC [ Co(en)2  Cl2 ]+ ion and draw the structures of its geometrical isomers.

Solution

 

Explanation: 

Question 13

(a) 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)

Solution

 

Explanation: 

OR

Complete and balance the following chemical equations :

(i) KMnO4 + KI + H2SO4_____ +  _____  +  _____ +  _____

(ii) K2Cr2O7 + H2SO4 + H2S →_____ +  _____  +  _____ +  _____

(iii) KMnO4 + H2SO4 + FeSO4 →_____ +  _____  +  _____ +  _____

Solution

 

Explanation: 

Question 14

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

C2H5NH2, C6H5NH2, (C2H5)2 NH

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

(c) What happens when benzene diazonium chloride reacts with phenol in weak alkaline medium ?

(Give balanced equation).

Solution

 

Explanation: 

Question 15

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

Solution

 

Explanation: 

Question 16

(a)  (i)  Calculate the emf and Δ for the cell reaction at 25°C :

Zn(s) | Zn2+(aq) || Cd2+(aq) | Cd(s)

.            (0.1M)       (0.01M)

Given E° Zn2+ / Zn = -0.763 and E° Cd2+ / Cd = -0.403V

(ii) Define the following terms :

(1) Equivalent conductivity

(2) Corrosion of metals

Solution

 

Explanation: 

(b)  (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. Calculate the molar and equivalent conductivity of the solution.

(ii) What is an electrochemical series ? How is it useful in predicting whether a metal can liberate hydrogen from acid or not ?

Solution

 

Explanation: 

Question 17

(a) (i) Explain why :

(1) Nitrogen does not form pentahalides

(2) Helium is used for filling weather balloons

(3) ICl is more reactive than I2

Solution

 

Explanation: 

(ii) Draw the structures of the following :

(1) HClO4

(2) H3PO3

Solution

 

Explanation: 

OR

(b) (i) Explain why :

(1) Mercury loses its meniscus in contact with ozone.

(2) Halogens are coloured and the colour deepens on moving down in the group from fluorine to iodine.

(3) Hydride of sulphur is a gas while hydride of oxygen is a liquid.

Solution

 

Explanation: 

(ii) Complete and balance the following reactions :

(1) NaCL + MnO2 + H2SO4 →_____ +  _____  +  _____ +  _____

(2) KMnO4 + SO2 + H2O →_____ +  _____  +  _____ +  _____

Solution

 

Explanation: 

Question 18

(a)   (i)   Give balanced equations for the following reactions:

(1) Benzaldehyde reacts with hydrazine.

(2) Acetic acid reacts with phosphorous pentachloride.

(3) Acetone reacts with sodium bisnlphite.

Solution

 

Explanation: 

(ii) Give one chemical test each to distinguish between the following pairs of compounds:

(1) Ethanol and acetic acid

(2) Acetaldehyde and benzaldehyde

Solution

 

Explanation: 

OR

(b) (i) Write chemical equations to illustrate the following name reactions:

(1) Clemmensen’s reduction

(2) Rosenmund’s reduction

(3) HVZ reaction

Solution

 

Explanation: 

(ii) Explain why :

(1) Acetaldehyde undergoes aldol condensation, but formaldehyde does not.

(2) Acetic acid is weaker acid as compared to formic acid.

Solution

 

Explanation: 

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