Q46 of 54 Page 94

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): The ionisation of hydrogen sulphide in water is low in the presence of hydrochloric acid.


Reason (R) : Hydrogen sulphide is a weak acid.


H2S ⇋ H+ + S2-


The ionisation of hydrogen sulphide in water is low in the presence of hydrochloric acid. This can be explained on the basis of common ion effect and Le Chatilier principle.


On addition of HCl, concentration of H+ will increase as it is common to both HCl and H2S. So the system accommodates the concentration of H+ by combining the H+ and S2- back toH2S and to do so the Equilibrium will shift in backward direction. Therefore, ionisation of H2S is low in presence of HCl due to common ion effect.

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44

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): Increasing order of acidity of hydrogen halides is HF < HCl < HBr < HI


Reason (R): While comparing acids formed by the elements belonging to the same group of periodic table, H–A bond strength is a more important factor in determining acidity of an acid than the polar nature of the bond.


 45

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : A solution containing a mixture of acetic acid and sodium acetate maintains a constant value of pH on addition of small amounts of acid or alkali.


Reason (R) : A solution containing a mixture of acetic acid and sodium acetate acts as a buffer solution around pH 4.75.


 47

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): For any chemical reaction at a particular temperature, the Equilibrium constant is fixed and is a characteristic property.


Reason (R) : Equilibrium constant is independent of temperature.


 48

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : Aqueous solution of ammonium carbonate is basic.


Reason (R) : Acidic/basic nature of a salt solution of a salt of weak acid and weak base depends on Ka and Kb value of the acid and the base forming it.