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Chapter 19: Q24P (page 489)

The graph shows the effect of pH on quenching of luminescence of tris(2,2'-bipyridine) Ru(II) by 2,6-dimethylphenol. The ordinate, KSV, is the collection of constants, kq /(ke + kd), in the Stern-Volmer equation. The greater KSV, the greater the quenching. Suggest an explanation for the shape of the graph and

estimate pKa for 2,6-dimethylphenol.

Short Answer

Expert verified

pKa=10.8

Step by step solution

01

Calculation of pKa value

The graph Ksv versus pH has two plateaus. First plateau is at low pH where the Ksv is approximately . The second plateau is at high pH where the Ksvis approximately . 2,6-dimethylphenol is a weak acid, so at the beginning it is in acidic form HA, while after it is in basic form A-. pKais the midpoint of the curve.

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