HARDMCQ SINGLENEET ChemistryPhysical ChemistryIonic equilibriumAchiever Section
Which pair of reagents, mixed in the appropriate proportion, could make a buffer in pH 3-4 range ?
A.NH₃ and NH₄Cl (Kb for NH₃ = 1.8 × 10–5)
B.HNO₂ and NaOH (Ka for HNO₂ = 4.6 × 10–4)✓ Correct
C.C₅H₅N and HCl (Kb for C₅H₅N = 1.8 × 10–9)
D.HClO and NaClO (Ka for HClO = 3.0 × 10–8)
Explanation
For buffer solutions, a pH pK and b pOH pK . Option (A) 5 3 4 b NH & NH Cl K 1.8 10 x . So, 5 b pOH pK log 1.8 10 pOH 4.74 x >> Thus, pH = 14 – pOH = 14 – 4.74 = 9.26 So, this does not lie between the 3 – 4 range. Option (B) 4 2 a HNO & NaOH K 4.6 10 x . So, 4 a pH pK log 4.6 10 pH 3.3 x >> So, this lies between 3 – 4 range and hence option (B) is the correct one.
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