chem help Pka

[pizza1994]

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Chlorosulfonic acid (HSO3Cl) is stronger than sulfuric acid when solvated in water, yet it is far less acidic in common organic solvents. When 1.16 g of HSO3Cl is dissolved in 10 mL of hexane, spectroscopic methods determine the [SO3Cl–] to be 2.2 x 10–3M. Which of the following is closest to the pKa of chlorosulfonic acid in hexane?

this is from TPR

answer is 5.4

not sure how you do this......anyone have any idea?

 

[dnrs]

You have .01 moles of the acid dissolved in .01 L of hexane, so molarity is 1.

By definition pKa = - log [H+][A-]/[HA], since so little of the acid dissolved compared to the amount we started with, we can leave [HA] as 1. Then, we know that [H+] and [A-] concentrations will be equal.

Hence,

pKa = -log ((2.2E-3)(2.2E-3)/(1)) = ~ 5.5