Case Study Questions
Question 1:
Read the passage given below and answer the following questions.
Reactants and products coexist at equilibrium, so that the conversion of reactant to products is always less than 100%. Equilibrium reaction may involve the decomposition of a covalent (nonpolar) reactant or ionization of ionic compound into their ions in polar solvents. Ostwald dilution law is the application of the law of mass action to the weak electrolytes in solution.
A binary electrolyte AB which dissociates into A+ and B– ions i.e.
for every weak electrolyte, Since α <<1 (1 – α) = 1
(i) A monobasic weak acid solution has a molarity of 0.005 M and pH of 5. What is its percentage ionization in this solution?
(a) 2.0
(b) 0.2
(c) 0.5
(d) 0.25
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Answer: b(ii) Calculate ionisation constant for pyridinium hydrogen chloride. (Given that H+ ion concentration is 3.6 × 10–4 M and its concentration is 0.02 M.)
(a) 6.48 × 10–2
(b) 6 × 10–6
(c) 1.5 × 10–9
(d) 12 × 10–8
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Answer: c(iii) The hydrogen ion concentration of a 10–8 M HCl aqueous solution at 298 K (Kw = 10–14) is
(a) 9.525 × 10–8 M
(b) 1.0 × 10–8 M
(c) 1.0 × 10–6 M
(d) 1.0525 × 10–7 M
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Answer: d(iv) Ostwald dilution law is applicable to
(a) weak electrolytes
(b) non-electrolyte
(c) strong electrolyte
(d) all type of electrolyte.
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Answer: a(v) If a is the fraction of HI dissociated at equilibrium in the reaction: 2HI ⇔ H2 + I2
then starting with 2 mol of HI, the total number of moles of reactants and products at equilibrium are
(a) 1
(b) 2
(c) 1 + α
(d) 2 + 2α
