If pKa value of HCN is 3.7 then pKa value of CN is
Correct answer: C. 10.3
- A. 7.3
- B. 3.7
- C. 10.3
- D. 14
Explanation
To find the pKb of CN-, which is the conjugate base of HCN, use the formula: pKa + pKb = 14. Given the pKa of HCN is 3.7, the calculation is: pKb = 14 - 3.7 = 10.3. Therefore, the correct answer is Option C: 10.3. Option A: 7.3 ignores this relationship. Option B: 3.7 mistakenly gives the pKa of HCN instead of the pKb of CN-. Option D: 14 is the sum of pKa and pKb, not the pKb value itself.
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About Acids, Bases and Salts
Acid and base behaviour is explained through the Bronsted-Lowry transfer of protons and the Lewis donation or acceptance of electron pairs. The topic includes pH, pOH, ionisation and water equilibrium, plus salt formation and hydrolysis, where a salt solution may become acidic, basic or neutral.
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