Q42E In humans, the final product of ... [FREE SOLUTION]

Chapter 20: Q42E (page 678)

In humans, the final product of purine degradation from DNA is uric acid, pKa = 5.61, which is excreted in the urine. What is the percent dissociation of uric acid in urine at a typical pH = 6.0? Why do you think uric acid is acidic even though it does not have a CO鈧侶 group?

Short Answer

Expert verified

Thedissociation percentage of uric acid is 71.01 %. The uric acid is acid due to its conjugate base got by proton loss stabilized by resonance.

Step by step solution

Finding [A-] by representing HA and A-

Given that pH=6 and pK_a=5.61. On representing and substituting Henderson-Hasselbalch equation,

$\log \frac{[HA]}{[A^{-}]} = {pK}_{a} - pH or \log \frac{[A^{-}]}{[HA]} = pH - {pK}_{a} \log \frac{[A^{-}]}{[HA]} = 6 - 5.61 \log \frac{[A^{-}]}{[HA]} = 0.39 \frac{[A^{-}]}{[HA]} = antilog of - 0.39 \frac{[A^{-}]}{[HA]} = 2.45 [A^{-}] = 2.45 [HA] - - - (1)$

Finding percent dissociation of uric acid

There is a presence of both ionized uric acid at equilibrium and also un-ionized forms.

$[HA] + [A -] = 100 % - - - (2) [HA] + 2.45 [HA] = 100 % 3.45 [HA] = 100 % [HA] = \frac{100}{3.45} [HA] = 28.99 % [A^{-}] = 100 - 28.99 [A^{-}] = 71.01 %$

The uric acid contains 3 hydrogen atoms attached to atoms of N. The proton removal will yield stabilization of resonance as conjugate base. The uric acid is acid nature.