DELHI PUBLIC SCHOOL Sail Township, Ranchi

Question Bank (SESSION-2016-17)

SUBJECT: Chemistry CLASS: – XII

Solution 1. Define mole fraction

2. Explain the Henry’s law about dissolution of a gas in a liquid.

3. State the main advantage of molarity over molality as the unit of concentration.

4. Define Ideal Solution.

5. State Raoult’s law for a solution of a volatile liquids.

6. A solution of glucose ¼ C6H12O6 ) in water is labelled as 10% by weight. What would be the molarity of the solution?

7. What are abnormal colligative properties? What is the cause of abnormal colligative properties explain giving example.

8. Calculate Van’t Hoff factor (i) for (a) K2SO4 (b) K4[Fe (CN)6] c) [ Co (NH3)6] Cl3

9. Explain why solution of chloroform and acetone shows negative deviation from Raoult’s law?

10. Derive the expression to calculate the molar mass of unknown solute from elevation in boiling point method. Define molal elevation constant.

11. Write the application of Henry’s law.

12. What is (a) Osmosis b) Osmotic Pressure c) Reverse osmosis d) Isotonic solution e) Cryoscopy

13. Calculate the boiling point of a solution prepared by adding 15 gm of NaCl to 250 gm of water. ( Kb for water = 0.512 K Kg mol – 1 )

14. A solution of urea in water has a boiling point of 373.128K. Calculate the freezing point of the same solution. ( Kf = 1.86 K m – 1 , Kb = 0.52 K m – 1 for water )

15. i) The molecular masses of polymers are determined by osmotic pressure method and not by measuring other colligative properties. Give two reasons. ii) At 300K, 36 gm of glucose, C6H12O6 present per litre in its solution has an osmotic pressure of 4.98 bar. If the osmotic pressure of another glucose solution is 1.52 bar at the same temperature, calculate the concentration of the other solution.

Solid State

1. ‘Crystalline solids are an isotropic in nature’. What does this statement mean?

2. What type of interactions hold the molecules together in a polar molecular solid?

3. How do metallic and ionic substances differ in conducting electricity?

4. ‘Stability of a crystal is related to the magnitude of its melting point.’ How?

5. A solid with cubic crystal is made of two elements P and Q. Atoms of Q are at the corner and P at the body centre. What is the formula of the compound?

6. In reference to crystal structure, explain the meaning of the coordination member.

7. Calculate packing efficiency of a metal crystal for a simple cubic lattice?

8. Silver crystallize in face centered cubic unit cell. Each side of the unit cell has a length of 409pm. What is the radius of Silver atom?

9. Aluminium crystallize in a cubic close packed structure. Radius of the atom in the metal is 125pm. i) What is the length of the side of the unit cell? ii) How many unit cells are there in 1 cm3 of aluminium?

10. Define - a) Frenkel defect b) Schottky defect c) Ferromagnetism

11. What is a semiconductor? Describe the two main types of semiconductor and explain mechanism for their conduction.

12. How would you account for the following - i) Frenkel defects are not found in alkali metal halides. ii) Schottky defects lower the density of volatile solids. iii) Impurity droped Silicon is a semiconductor.

13. What are F-centres? Explain giving a suitable example.

14. Explain - a) Valency defect b) Interstitial defect c) Metal excess defect d) Anisotropy e) Thermodynamic defect.

15. Tungsten crystallizes in body centred cubic unit cell. If the edge of the unit cell is 316.5pm, What is the radius of tungsten atom.

Electrochemistry

1. What is meant by limiting molar conductivity?

2. Under what condition is Ecell = O or ΔrG = O ?

3. How will PH of brine (aq. NaCl solution) be affected when it is electrolysed?

4. In the electrolysis of aq. Sodium bromide, there are two possible anodic reactions 2H2O ( l ) O2 (g) + 4H+ (aq) + 4e – , E0 = 1.23V 2Br – Br2 (g) + 2e –, E0 = 1.08V Which reaction occurs at anode and why?

5. Mention the reaction occurring at anode and cathode during working of a mercury cell. Why does the voltage of a mercury cell remains constant during it’s operation?

6. i) Why is alternating current used for measuring resistance of an electrolytic solution?

ii) What does the negative sign in expression - 0

2znzn

E + = -0.76V means?

7. How long a current of 3 ampere has to be passed through a solution of Silver nitrate to coat a metal surface of 80 cm2 with a 0.005 mm thick layer? Density of Ag is 10.5 gm Cm – 3 . [ Atomic mass of Ag=108u ]

8. What is corrosion? What are the factors which affect corrosion? CO2 is always present in natural water. Explain its effect on rusting of iron.

9. The E0 values at 298K corresponding to the following two reduction process are: i) Cu+ / Cu = +0.52V ii) Cu2+ / Cu = +0.16V Formulate the galvanic cell for their combination. What will be the cell potential? Calculate ΔrGe for the cell reaction.

10. The molar conductivity of 0.025 mol/L methanoic acid is 46.1 S Cm2mol – 1 . Calculate it’s degree of dissociation and dissociation constant:

Give 0

+Hλ = 349.6 S Cm2mol – 1 and 0

−HCOOλ = 54.6 S Cm2mol – 1 .

11. a) Calculate ΔrGθ for the reaction Mg(s) + Cu2+ (aq) Mg2+(aq) + Cu (s) Given 0

CellE = +2.71V, F = 96500C/mo;

b) Name the type of cell which was used in Apollo space programme for providing electric power.

c) Explain the working, Principle of that cell by showing anode and cathode rection.

12. i) Write two advantages of H2O2 fuel cell over ordinary cell. ii) Equilibrium constant Kc for the given cell reaction is 10. Calculate 0

CellE .

A(s) + B2+ (aq) A2+ (aq) + B (s)

13. a) What type of a battery is lead storage battery? Write the anode and cathode reaction and the overall cell reaction occurring in the operation of a lead storage battery. b) Calculate the potential for half cell containing 0.1M K2Cr2 O7 (aq), 0.2M Cr3+ (aq) and 1.0 x 10 – 4 M H+ (aq) The half cell reaction is -

)(7)(26)(14)( 232

72 lOHaqCreaqHaqOCr +⇒++ +−+−

and the standard electrode potential is given as 0E = - 1.33V

14. a) In the button cell used in watches the following reaction occurs. Zn(S) + Ag2O(S) + H2O (l) Zn2+(aq) + 2Ag(S) + 2OH – (aq) ( 0E = - 0.80V)

b) Explain with examples the term weak and strong electrolytes.

15. a) Define molar conductivity of a solution and explain how molar conductivity changes with change in concentration of solution of a weak and a strong electrolyte. b) The resistance of a conductivity cell containing 0.001M KCl solution at 298K is 1500Ω. What is the cell constant if the conductivity of 0.001M KCl solution at 298K is 0.146 x 10 – 3 S cm – 1 ?

16. a) State Kohlrausch’s Law of independent migration of ions. Write an expression for the molar conductivity of acetic acid at infinite dilution according to Kohlrausch Law.

b) Calculate 0mλ for acetic acid.

Given that 0mλ (HCl) = 426 S cm2 mol – 1 .

0mλ (NaCl) = 126 S cm2 mol – 1 .

0mλ (CH3 COONa) = 91 S cm2 mol – 1 .

17. a) How many moles of mercury will be produced by electrolyzing 1.0M Hg(NO3)2 solution with a current of 2.00 ampere for 3 hours? [Hg(NO3)2 = 200.6 gm/mol] b) A voltaic cell is set up at 25°C with the following half cells Al3+ (0.001M) and Ni2+ (0.50M) write an equation for the reaction that occur when the cell generates an electric current and determine the cell potential.

(Given 0

2NiNi

E + = - 0.25 V, 0

3AlAl

E + = 1.66V )

 

 

 

 

 

 

 

 

 

Surface Chemistry 

1. What are the dispersion phase and dispersion medium in butter?

2. What causes Brownian movement in a colloidal solution?

3. What modification can you suggest in the Hardy Schulze rule?

4. Define the term ‘Tyndall effect’.

5. Define the following – i) Peptization ii) Reversible solution

6. Differentiate between homogenous and heterogeneous catalysis with one example of each.

7. Explain the following – a) Some substances can act both as colloid and crystalloid. b) Artificial rain is caused by spraying salt over clouds.

8. What is meant by coagulation of a colloidal solution? Name three methods by which coagulation of lyophobic solution can be carried out.

9. Explain what is observed when - a) An electric current is passed through a solution. b) A beam of light is passed through a solution. c) An electrolyte NaCl is added to ferric hydroxide solution.

10. a) Give an example where physisorption changes to chemisorption with rise in temperature? Explain reason for change. b) Do the vital functions of the body such as digestion gets affected during fever? Explain your answer.

11. a) Which will be adsorbed more readily on the surface of charcoal and why? NH3 or CO2. b) What are the two types of emulsions and how do they differ from one another?

12. a) What happens when a freshly precipitated Fe(OH)3 is shaken with water containing a small quantity of FeCl3? b) Why a finely divided substance more effective as an adsorbent?

13. a) What are the two types of emulsions and how do they differ from one another? Give one example of each. b) Which one of the following electrolytes is most effective for the coagulation of Fe(OH)3 solution & why? Nacl, Na2SO4 and Na3PO4.

Chemical Kinetics

1. Identify the reaction order from each of the following rate constants. a) K = 2.3 x 10 – 5 L mol – 1 S – 1 . b) K = 3 x 10 – 4 S – 1

2. Why does the rate of a reaction not remain constant throughout the reaction process?

3. For a chemical reaction R P the variation in the concentration (R) Vs time (t) plot is given as -

a) Predict the order of the reaction. b) What is the slope of the curve?

4. For a certain reaction large fraction of molecules has energy more than the threshold energy, yet the rate of reaction is very slow. Why?

5. State a condition in which bimolecular reaction is kinetically first order reaction. Give one example also.

6. Show that time required for 99% completion is twice the time required for the completion of 90% reaction.

7. Define – a) Elementary reaction in a process b) Rate of a reaction

8. The rate of a reaction quadruples when the temperature changes from 293K to 313K. Calculate the energy of activation of the reaction assuming that it does not change with temperature. [ R = 8.314 J/K/mol ] Log4 = 0.6021

9. The following data were obtained during the first order thermal decomposition of SO2Cl2 at a constant volume. SO2 Cl2 (g) SO2(g) + Cl2 (g) (Given log4 = 0.6021, log2 = 0.3010)

10. a) Define the following - i) order of a reaction ii) Elementary step in a reaction. b) A first order reaction has a rate constant value of 0.00510 min – 1 . If we begin with 0.10M concentration of the reactant, how much of the reactant will remain after 3.0 hours?

Expt. Time (S – 1 ) Total pressure /atom 1 0 0.4 2 100 0.7

11. a) Distinguish between molecularity and order of a reaction. b) The activation energy for the reaction 2HI(g) H2 (g) + I2 (g) is 209.5 KJ/mol. Calculate the fraction of molecules having energy equal to or greater than activation energy. [R = 8.314 J/K/mol]

Haloalkanes and Haloarenes

1. Which one of the two compounds CH3Br and CH3I will react faster in SN2 reaction with OH – .

2. Write the structure of the compound 1 – chloro – 4- ethylcyclohexane.

3. Write IUPAC name of the following compound:

4. Identify the chiral molecule in the following pair:

,

5. Complete the following chemical equation : a) CH3 CH2 CH = CH2 + HBr

Peroxide

Organic⎯⎯ →⎯

b) + HI ⎯→⎯

6. What are ambident nucleophiles? Explain by giving an example.

7. Cholrobenzene is extremely less reactive towards nucleophillic substitution reaction. Give two reasons.

8. Write chemical equation when - a) ethyl chloride is treated with aqueous KOH. b) C6H5Cl is treated with CH3COCl in presence of anhydrous AlCl3.

9. Answer the following: a) Haloalkanes easily dissolve in organic solvents. Why? b) What is known as racemic mixture? Give an example. c) Of the two bromo derivatives C6H5CH (CH3)Br and (C6H5)CH (C6H5)Br, which one is more reactive in SN1 substitution reaction and why?

d) Grignard Reagent can’t prepared in moist condition.

10. a) Write chemical test to distinguish between - i) Chlorobenzene and benzyl chloride. Ii) Chloroform and carbon tetrachloride. b) Why is methyl chloride hydrolysed more easily than chlorobenzene?

Although chlorine is an electron with drawing group. Yet it is ortho, para directing in electrophillic aromatic substitution reactions. Explain, why is it so?

11. a) Write the IUPAC name of DDT? b) Which compound of the following couples will react faster in SN2 displacement and why? i) 1- bromopentane or 2 – bromopentane ii) 1 – bromo – 2 – methyl butane or 2 – bromo – 2 – methyl butane

12. Explain as to why haloarenes are much less reactive than haloalkanes towards nucleophilic substitution reaction.

13. Give one example of : a) Finkelsteen’s reaction d) Sandmeyer’s Reaction b) Wurtz filttig reaction c) Swarts reaction

14. a) How would you differentiate between SN1 and SN2 mechanism of substitution reaction? given one example of each. b) Which compound in each of the following pairs will react faster in SN2 reaction with OH – and why? i) CH3 Br or CH3 I ii) (CH3 )3 C Cl or CH3 Cl.

Alcohol, Phenols and Ethers

1. Why ethanol has higher boiling point than methoxymethane.

2. Arrange the following compounds in the increasing order of their acid strengths. 4 – Nitrophenol; Phenol; 2,4,6 – Trinitrophenol.

3. How is toluene obtained from phenol.

4. Write the reactions and conditions involved in the conversion of - a) Propene to Propan – 1 – ol. ii) Phenol to Salicylic acid iii) Phenol Asprine

5. Account for the following: a) Propanol has higher boiling point than butane. c) Phonol is more acidic than Ethyl Alcohol b) 0 – Nitrophenol is more acidic than 0 – Methoxy phenol.

6. Describe the mechanism of alcohols reacting both as nuclophiles and electophiles in their reactions.

7. a) Give one chemical test to distinguish between the following pairs of compounds - i) Phenol and benzoic acid ii) 1 – Propanol and 2 – Propanol. b) Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.

8. a) Write the IUPAC name of the following

b) Describe the chemical test to distinguish between ethanol and phenol.

9. A compound A( C2H6O) on oxidation by PCC gave B, which in treatment with aqueous alkali and subsequent heating furnished C. B on oxidation by KMnO4 forms a monobasic carboxylic acid with molar mass 60g mol – 1 . Deduce the structure of A, B and C.

10. Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.

11. Explain the mechanism of the reaction. a) Addition of RMgX to carbonyl group of a compound forming an adduct followed by hydrolysis. b) Describe the chemical test to distinguish between ethanol and phenol.

12. Write short notes:

a) Reimer Tieman reation

b) Kolbe’s Reaction

c) William Son’s Synthesis

d) Acctylation Reaction of Phenol

e) Hydroboration Reaction.

13. Name the reagent and write the chemical equation for the preparation of the following compounds by Williamson’s synthesis. a) Ethoxy benzene b) 2 – methyl – 2- methoxy propane.

14. State the product of the following reactions:

a) CH3 CH2 CH2 O CH3 + HBr b) + HBr c) ( CH3)3 C – OC2H5 ⎯→⎯HI

15. Write the IUPAC name of the following:

16. a) Give reason for the following : i) The boiling point of ethanol is higher than that of methanol. ii) Phenol is a stronger acid than an alcohol. b) How would you obtain the following? i) Phenol from benzene. ii) 2 – methylpropan – 2- ol from methyl magnesium bromide. iii) Propan – 2- ol from propene.