The luminescence of a molecule, M, is quenched by the molecule Q, which is a wea
ID: 592693 • Letter: T
Question
The luminescence of a molecule, M, is quenched by the molecule Q, which is a weak acid. The Ster Mapf Volmer quenching constant (Ksv) for the quenching of M by Q was measured at several pH values. The results are shown in the table and plotted below 1600 1400 1200 1000 800 600 400 200 5.00 5.45 5.88 6.25 6.90 7.15 7.30 7.79 8.20 8.86 9.80 10.23 10.87 Ksv 200 210 230 225 275 345 389 600 979 1256 1459 1489 1500 9 10 12 Choose the best explanation for the shape of the plot O The acidic and basic forms of Q are both weak quenchers The acidic form of Q is a strong quencher, while the basic form of Q is a weak quencher The basic form of Q is a strong quencher, while the acidic form of Q is a weak quencher. The quenching capabilities of Q are independent of the pH The acidic and basic forms of Q are both strong quenchers Scroll down to view the entire question O OExplanation / Answer
The luminescence of molecule M by a weak acid molecule Q is plotted above.
From the given plot, we can say that,
The acidic and basic forms of Q are weak quenchers
Using the plot,
we can estimate pKa for Q
pKa = 5.45
The 1/2 way to the perpendicular area at the begining is taken as pH = pKa
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