Chemistryimportant questionairres for cbse

2015

LANCERS CONVENT CHEMISTRY Q.1 Q.2 Q.3 Q.4 Q.5 Q.6

Q.7 Q.8 Q.9 Q.10

Q.11

Q.12

Q.13 Q.14 Q.15

Q.16 Q.17 Q.18 Q.19

Q.20

(ELECTROCHEMISTRY) Explain the role of salt bridge in an electrochemical cell. What are essential conditions for a salt to be used in a salt bridge? Explain the effect of concentration on molar molar conductivity for weak electrolytes and strong electrolytes giving a suitable graph. Explain how standard reduction potential of magnesium can be determined. Why molar conductivity at infinite dilution can not be determined by graphical technique? Further suggest any other alternative way to determine it. Cell potential of a Zn- Cu cell is 1.1 volt. Explain the chemical changes which may take place when (i) An external source of less than 1.1 volt is connected to it. (ii) An external source of more than 1.1 volt is connected to it. (iii) An external source equal to 1.1 volt is connected to it Write the chemical reaction which take place during the (i) Use of lead storage battery (ii) Recharging of lead storage battery Explain the working of H2 –  O  O2 fuel cell with diagram and chemical equations. Corrosion is an electro chemical process. Justify. Explain the concept of cathodic protection from rusting. The resistance resistance of a semi molar solution of an electrolyte enclosed between two platinum electrodes electrodes 2 1.5 cm apart and having an area of 2.0 cm  was found to be 30 ohm. Calculate the molar conductivity of the solution. The molar conductivities at infinite dilution for NaI, NaAc and (Ac) (Ac)2 Mg are 12.69, 9.10 and 2  – 1 0 18.78 S cm  mol  respectively at 25 C. What is the molar conductivity of MgI2 at infinite dilution? 2  – 1 The molar conductance of ammonium hydroxide at 0.001 M concentration is 34.0 S cm mol respectively. Calculate the degree of dissociation of NH4OH. Molar conductance at infinite dilution for  – 1 2  – 1  NH4OH is 271.1 ohm  cm  mol . 2  – 1 The molar conductivity at infinite dilution of Al2(SO4)3 is 858 S cm  mol . Calculate the molar 3+ 0 2 –  2  – 1 ionic conductivity of Al  ion given that    (SO4 ) = 160 S cm  mol .  –  2+ How much charge is is required for the reduction of 0.75 mol of MnO4  to Mn .  –   –  Iodine (I2) and bromine (Br 2) are added to a solution containing iodide (I ) and bromide (Br  ) ions. What reaction would occur if the concentration conc entration of each species is 1 M ? The electrode potentials\ for the reactions are :  –   –  0 I2 + 2e 2I , E  = + 0.54 V  –   –  0 Br 2 + 2e 2Br  , E  = + 1.08 V The same quantity of electrical charge that deposited 0.583 g of silver was passed through a solution of gold salt and 0.355 g of gold was formed. What is the oxidation ox idation state of gold in this salt? What current current in amperes is required to produce 50.0 ml of O2 gas measured at STP by electrolysis of water for a period of 3 hrs ? In the the button cell widely used in watches and other devices the following reaction takes place : 2+  –  0 0 Zn(s) + Ag2O(s) + H2O(l) Zn  (aq) + 2Ag(s) + OH  (aq). Determine E  and  r G  for the reaction. What will will be the spontaneous reaction reaction when the following following half reactions are are combined? 3+  –  2+ 0  (a) Fe  + e Fe , E  = + 0.77 V  –  +  –  2+ 0 0  (b) MnO4  + 8H  + 5e Mn  + 4H2O, E  = + 1.49 V) What is the value of E cell? Calculate the reduction potential of the following electrode at 298 K

CHEMISTRY CLASS XII

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2015

LANCERS CONVENT

Q.21

Pt, Cl2 (2.5 atm) | HCl (0.01 M); 0  –  E Cl2 | 2 Cl  = 1.36 V + 0 2+ For what concentration of Ag  (aq) will e.m.f. of the cell be zero at 25  C if concentration of Cu  (aq) 2+ + 0 + 0 2+ is 0.01 M ? Cu(s) | Cu  (0.01M) || Ag  (aq) | Ag (s) [ Given : E  (Ag  | Ag) = 0.80 V and E  (Cu  | Cu) = 0.338 V]

CHEMISTRY (THE SOLID STATE)

1. 2.

3. 4.

5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

A solid has a cubic structure in which X atoms are located at the corners of the cube, Y atoms are at the cube centers and O atoms at the edge centers. What is the formula of the compound ? A compound formed by elements X and Y crystallizes in the cubic structure where Y atoms are at the corners of the cube and X atoms are at the alternate faces. What is the formula of the compound ? In corundum, oxide ions are arranged in h.c.p. array and the aluminium ions occupy two –  thirds of octahedral voids. What is the formula of corundum ? In a crystalline solid, having formula of AB2O4, oxide ions are arranged in cubic close packed lattice while cations A are present in tetrahedral voids and cations B are present in octahedral v oids. a. What percentage of the tetrahedral voids is occupied by A ?  b. What percentage of the octahedral voids is occupied by B ? In a solid, oxide ions are arranged in ccp. cations A occupy one –  sixth of the tetrahedral voids and cations B occupy one –  third of the octahedral voids. What is the formula of the compound? In chromium (III) chloride, CrCl 3, the chloride ions have ccp (cubic close packing) arrangement and Cr (III) ions are present in octahedral holes. What fraction of the o ctahedral holes is occupied ? What fraction of the total no. of holes is occupied ? Describe the structure of wusite (Fe0.95 O) and magnetite (Fe3O4). The composition of a sample of wustite is Fe0.93 O1.00  .What percentage of the iron is present in the form of Fe(III) ? Potassium crystallizes in a body centred cubic lattice. What is the approximate number of unit cells in 4.0g of potassium? + CsCl forms b.c.c. lattice. Cs and Cl  are in contact along the body diagonal of the cell. The length of + the side of the unit cell is 412 pm and Cl  has a radius of 181 pm. Calculate radius of Cs . 0 The effective radius of an iron atom having rock salt structure is 1.42 A . If atomic mass of iron is 56 amu, calculate its density. -3 Density of NaCl crystal is 2.165 g cm . Calculate value of Avogadro’s number if distance between +  Na  and Cl  in NaCl is 281 pm. Why is Frenkel defect not found in pure alkali metal halides ? How would you explain that (i) Non –  stoichiometric NaCl is yellow (ii) Non-stoichiometric ZnO is yellow ? Explain the electrical conduction mechanism in silicon doped with (i) P (ii) Ga. 2+ 2The ionic radii of Mg  and O  ions are 66 pm and 140 pm respectively. What type of interstitial 2+ 2+ void Mg  is likely to occupy? What is the probable coordination number of Mg  ion? + A solid A  B  has NaCl type close packed structure. If the anion has a radius of 241.5 pm, what + should be the minimum radius of cation ? Can a cation C  having radius 50 pm be fitted into the + tetrahedral hole of the crystal A  B  ?

CHEMISTRY CLASS XII

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2015

LANCERS CONVENT 18. 19. 20. 21. 22.

How many unit cells are there in a 1.0 g cube shaped ideal crystal of NaCl ? + What minimum value of r   / r  is needed to prevent anion –  anion contact in NaCl crystal? + Why does ZnS (r   / r  = 0.402) not crystallize in the NaCl structure? -10 Lithium forms a b.c.c. lattice. If edge length of un it cell is 3.5 x 10  m and the experimental 2 -3 density is 5.3 x 10  Kg m , calculate percentage occupancy of Li metal. Calculate the percentage of vacant space in Si cubic unit cell. The unit cell content of Si is 8 and r=

3a 8

.

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CHEMISTRY (SOLUTION)

1.

-1

A solution of glucose in water is 10% by mass. If density of solution is 1.2 g ml . Calculate (a) Molarity

(b) Molality

(c) Mole fraction of glucose in the solution

2.

One litre solution of M / 2 HCl is heated in a beaker. It was observed that when volume of the solution is reduced to 600 ml, 3.25 g of HCl is lost. Calculate the molarity of the new solution.

3.

Conc. H2SO4 supplied by a chemical supplier is 80%. (    = 1.8 gm ml ). Calculate volume of this solution required to prepare 1L of 0.2 M H2SO4 solution.

4.

The mole fraction of benzene in a solution with toluene is 0.50. Calculate the mass percent of  benzene in the solution.

5

-1

The mole fraction of water in a sulphuric a cid solution is 0.85. Calculate the molality of the solution. -1

6. How many ml. of H2SO4 of density 1.84 g ml  containing 95.6 mass % of H2SO4 should be added to -1 one litre of 40 mass % solution of H 2SO4 of density 1.31 g ml  in order to prepare 50 mass % solution -1 of H2SO4 of density 1.4 gm . 7. 20 ml of 0.2 M Al2 (SO4)3 mixed with 20 ml of 0.6 M BaCl2. Calculate the conc. Of each ion in the solution. 8. What is the strength in g per litre of a solution of H2SO4, 12 ml of which neutralized 15 ml of M / 10  NaOH solution ?. -1

0

9. Partial pressure of O2 in air is 0.2 atm. Calculate conc. (in mol lit ) of dissolved O2 in water at 25 C . 4

0

(K H = 4.34 x 10  atm at 25 C) 10. Benzene and toluene form nearly ideal solution at 313 K, the vapour pressures of pure benezene and toluene are 160 mm of Hg and 60 mm of Hg respectively. Calculate total pressure of the solution containing : (i)

equal weights of benzene and toluene

(ii)

equal molecules of benzene and toluene

CHEMISTRY CLASS XII

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2015

LANCERS CONVENT

11. The vapour pressure of liquid A is 40 mm of Hg at 310 K. The vapour pressure of solution of A with B is 32 mm of Hg. Calculate mole fraction of A in the solution. 12. At 300 K, 36 g of glucose present per litre in it solution has a n osmotic pressure of 4.98 bar. Osmotic pressure of solution is 1.52 bar at the same temperature. What would be its concentration? **************

CHEMISTRY CLASS XII

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