Class 12th Chemistry Most important Questions of Solutions, Electrochemistry and Chemical Kinematics

Class 12th Chemistry 

Most important Questions of Solutions, Electrochemistry and Chemical Kinematics 

Chapter -1.  Solutions 

Q1. Calculate the molarity of each of the following solutions: 

(a) 30 g of Co(NO3)2. 6H2O in 4.3L of solution
(b) 30 mL of 0.5 M H2SO4 diluted to 500 mL.

Q2. Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of 20% 
(mass/mass) aqueous KI is 1.202 g mL-1.

Q3. H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.

Q4. Boiling point of water at 750 mm Hg is 99.63° C. How much sucrose is to be added to 500 g of water such that it boils at 100°C.

Q5. Calculate the mass of ascorbic acid (Vitamin C, C6H8O6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5°C. Kf = 3.9 K kg mol-1
.
Q6. Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL of water at 37°C.

Q7. A solution is obtained by mixing 300 g of 25% solution and 400 g of 40% solution by mass.  Calculate the mass percentage of the resulting solution.

Q8. An antifreeze solution is prepared from 222.6 g of ethylene glycol (C2H6O2) and 200 g of water. Calculate the molality of the solution. If the density of the solution is 1.072 g mL–1, then what shall be the molarity of the solution?

Q9. Calculate the mass of a non-volatile solute (molar mass 40 g mol–1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.

Q10. A 5% solution (by mass) of cane sugar in water has freezing point of 271K. Calculate the freezing point of 5% glucose in water if freezing point of pure water is 273.15 K.

Q11. Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C6H6), 1 g of AB2 lowers the freezing point by 2.3 K whereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg mol–1. Calculate atomic masses of A and B.

Q12. Calculate the depression in the freezing point of water when 10 g of CH3CH2CHClCOOH is added to 250 g of water. Ka = 1.4 × 10–3, Kf = 1.86 K kg mol–1.

Q13. 19.5 g of CH2FCOOH is dissolved in 500 g of water. The depression in the freezing point of water observed is 1.0 C. Calculate the van’t Hoff factor and dissociation constant of fluoroacetic acid.

Q14. Determine the amount of CaCl2 (i = 2.47) dissolved in 2.5 litre of water such that its osmotic pressure is 0.75 atm at 27° C.

Q15. Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K2SO4 in 2 litre of water at 25° C, assuming that it is completely dissociated.

Chapter -3 .  ELECTROCHEMISTRY

Q1. Can you store copper sulphate solutions in a zinc pot?
Q2. The molar conductivity of 0.025 mol L–1 methanoic acid is 46.1 S cm2 mol-1. Calculate its degree of dissociation and dissociation constant. Given λ0(H+) = 349.6 S cm2 mol–1 and  λ0(HCOO–) = 54.6 S cm2 mol–1.

Q3. Calculate the standard cell potentials of galvanic cell in which the following reactions take place:
(i) 2Cr(s) + 3Cd2+ (aq) → 2Cr3+ (aq) + 3Cd
(ii) Fe2+(aq) + Ag+ (aq) → Fe3+(aq) + Ag(s)
Calculate the ΔrG⊖ and equilibrium constant of the reactions.

Q4. Write the Nernst equation and emf of the following cells at 298 K:

(i) Mg(s)|Mg2+(0.001M)||Cu2+(0.0001 M)|Cu(s)
(ii) Fe(s)|Fe2+(0.001M)||H+
(1M)|H2(g)(1bar)| Pt(s)
(iii) Sn(s)|Sn2+(0.050 M)||H+
(0.020 M)|H2(g) (1 bar)|Pt(s)
(iv) Pt(s)|Br–(0.010 M)|Br2(l )||H+(0.030M)| H2(g) (1 bar)|Pt(s).

Q5. How much electricity in terms of Faraday is required to produce

(i) 20.0 g of Ca from molten CaCl2?
(ii) 40.0 g of Al from molten Al2O3?

Q6. A solution of Ni(NO3)2 is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?

Q7. Three electrolytic cells A,B,C containing solutions of ZnSO4, AgNO3 and CuSO4, respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?

Chapter -4 .  CHEMICAL KINETICS

Q1. A first order reaction has a rate constant 1.15 × 10-3s-1. How long will 5 g of this reactant take to reduce to 3 g?

Q2. For the reaction:

2A + B → A2B

the rate = k[A][B]2 with k = 2.0 × 10–6 mol–2 L 2s–1. Calculate the initial rate of the reaction when [A] = 0.1 mol L–1, [B] = 0.2 mol L–1. Calculate the rate of reaction after [A] is reduced to 0.06 mol L–1.

Q3. A reaction is first order in A and second order in B.
(i) Write the differential rate equation.
(ii) How is the rate affected on increasing the concentration of B three times?
(iii) How is the rate affected when the concentrations of both A and B are doubled?

Q4. The half-life for radioactive decay of 14C is 5730 years. An archaeological artifact containing wood had only 80% of the 14C found in a living tree. Estimate the age of the sample.

Q5. For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.

Q6. A first order reaction takes 40 min for 30% decomposition. Calculate t1/2.

Q7. The decomposition of hydrocarbon follows the equation k = (4.5 × 1011s–1) e-28000K/T Calculate Ea.

Q8. The time required for 10% completion of a first order reaction at 298K is equal to that required for its 25% completion at 308K. If the value of A is 4 × 1010s–1. Calculate k at 318K and Ea.

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