JEE Main Previous Year Papers Questions With Solutions Chemistry Chemical and Ionic Equilibrium

JEE Main Previous Year Papers Questions With Solutions Chemistry Chemical and Ionic Equilibrium

1.M NaCl and 1 M HC1 are present in an aqueous solution. The solution is (2002)
1)not a buffer solution with p^H < 7
2)not a buffer solution with p^H > 7
3)a buffer solution with p^H < 7
4)a buffer solution with p^H > 7
Ans.(1) A buffer is a solution of weak acid and its salt  with strong base and vice versa. HCl is strong acid and NaCl is its salt with strong base. pH is less than 7 due to HCl.

2.Species acting as both Bronsted acid and base is   (2002)
1)HS0₄-1 2) Na₂C0₃ 3) NH₃ 4) OH-1
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3.Let the solubility of an aqueous solution of Mg(OH)₂ be x, then its k_sp is      (2002)
1)4x³      2) 108x⁵         3) 27x⁴           4) 9x
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4.The solubility of Mg(OH)₂ is S moles / litre. The solubility product under the same condition is            (2002)
1)4S³         2) 3S⁴                 3) 4S²             4) S³
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5.Change in volume of the system does not alter the number of moles in which of the following equilibria ? (2002)

Ans.(1) In this reaction the ratio of number of moles of reactants to products is same, hence change l in volume will not alter the number of moles

6.In which of the following reactions, increase in the volume at constant temperature does not affect the number of moles at equilibrium(2002)

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Ans.(2) An acidic solution cannot have a pH > 7.

9.The solubility in water of a sparingly soluble salt AB₂ is 1.0 x 10^-5 molL”¹. Its solubility product number will be            (2003)
1)4 x 10^-10        2) 1 x 10-¹⁵
3) 1 x 10-¹⁰      4) 4 x 10^-15
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Ans.(2) Due to exothermicity of reaction low or optimum temperature will be required. Since 3 v moles are changing to 2 moles. High pressure will be required.

12.Which one of the following substances has the highest proton affinity ?     (2003)
1)H₂S 2) NH₃ 3) PH₃ 4) H₂0
Ans.(2) H₂S is more acidic.

13.In a 0.2 molal aqueous solution of a weak acid HX the degree of ionization is 0.3. Taking k_f for water as 1.85, the freezing point of the  solution will be nearest to   (2003)
1) – 0.360°C                    2) – 0.260°C
3) + 0.480°C                   4) – 0.480°C
Ans.(4) Decrease by 1.85 x 0.3 x 1.3 = 0.48°C

14.The conjugate base of H₂P0₄– is (2004)
1) P0₄³– 2) HP0₄^2- 3)H₃P0₄ 4)P₂0₅
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Ans.(2) Applying law of mass action, the expression for K is obtained. Only 0₂ is a gas and hence its active mass only appear in K.

Ans.(1) Kp = Kc (RT)^{in   .}Here, An is 1 – (1 + 1) = – 1.

Ans.(4) As per property of equilibria, reverse the equation and divide it by 2.

Ans.(2) If ‘s’ is the solubility Ksp = 108s⁵ 1 x 4⁴ x s¹⁺⁴ = 256 s⁵ = Ksp

19.The solubility product of a salt having general formula MX₂, in water is : 4xl0^-12. The concentration of M²⁺ ions in the aqueous solution of the salt is     (2005)
1) 2.0 x 10.6 M              2) 1.0 x 10.4 M
3) 1.6 x 10.4 M              4) 4.0 x 10.10 M
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Ans.(4) An increase in the concentration of a reactant at equilibrium, the forward reaction is favoured. Hence, adding F₂

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22.Hydrogen ion concentration in mol L^-1 in a solution of pH = 5.4 will be  (2005)
1) 3.98 x 10⁸                2) 3.88 x 10⁶
3) 3.68 x 10^-6                  4) 3.98 x 10^-6
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23.What is the conjugate base of OH^– ? (2005)
1) 0₂          2) H₂0          3) 0^–            4) O^-2
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24.An amount of solid NH₄HS is placed in a flask already containing ammonia gas at a certain temperature and 0.5 atm. Ammonium hydrogen sulphide decomposes to yield NH₃ and 1I₂S gases in the flask. When the decomposition reaction reaches equilibrium, the total pressure in the flask rises to 0.84 atm. The equilibrium constant for NII₄HS decomposition at this temperature is (2005)
1) 0.30   2) 0.18  3) 0.17  4) 0.11
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28.The pKa of a weak acid (HA) is 4.5. The pOH of an aqueous buffered solution of HA in which 50% of the acid is ionized is (2007)
1) 4.5          2) 2.5           3) 9.5           4) 7.0
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30.The first and second dissociation constants of an acid H₂A are 1.0 x 10^-5 and 5.0 x 10“¹⁰ respectively. The overall dissociation constant of the acid will be      (2007)
1) 5.0 x 10^-5                    2) 5.0 x 10¹⁵
3) 5.0 x 10^-15                  4) 0.0 x 10⁵
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Ans.(3) Equation (c) = equation (a) + equation (b). Thus K, = K,.K₂

33.Four species are listed below
i) HC0^–3; ii) H₃0⁺ iii) HSO^–4 iv) HS0₃F
Which one of the following is the correct sequence of thfflr acid strength ?            (2008)
1) iv < ii < iii <i                       2) ii < iii < i < iv
3) i < iii < ii < iv                       4) iii < i < iv < ii
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34.The pK_a of a weak acid, HA, is 4.80. The pK_b of a weak base, BOH, is 4.78. The pH of an aqueous solution of the corresponding salt, BA, will be           (2008)
1) 9.58            2) 4.79             3) 7.01             4) 9.22
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38.Solubility product of silver bromide is 5.0x 10^-13. The quantity of potassium bromide (molar mass is 120g of mol^-1) to be added to 1 litre of 0.05 M solution of silver nitrate to start the precipitation of AgBr is (2010)
1) 1.2 x 10-¹⁰g             2) 1.2 x 10-⁹g
3) 6.2 x 10-⁵g                4) 5.0 x 10-⁸g
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39.At 25°C, the solubility product of Mg(OH)₂ is 1.0 10^_n. At which pH, will Mg²⁺ ions start precipitating in the form of Mg(OH)₂ from a solution of 0.001 M Mg²⁺ ions ? (2010)
1)9              2) 10           3)11              4)8
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40.The reduction potential of hydrogen half-cell will be negative if : (2011)
1)P(H₂) = 2 atm and [H⁺] = 1.0 M
2)P(H₂) = 2 atm and [H⁺] = 2.0 M l
3)P(H₂) = 1 atm and [H⁺] = 2.0 M
4)P(H₂) = 1 atm and [H⁺] = 1.0 M
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42.The pH of a 0.1 molar solution of the acid HQ is 3. The value of the ionization constant Ka of this acid is     (2012)
1) 3×10^_1                        2) 1×10^-3
3) 1×10^-5                         4) 1×10^-7
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Ans.(4) If SRP value is high-powerful oxidising agent.

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