Question

When a tablet of aspirin dissolves in the stomach acetylsalicylate con lo acetylsalicylic acid Does acid or more acetylsalicylation at this pH hell, what is the rate of there is one acetylsalicylie -0.0032 lots are ad prevent

My question is about a particular part inside of this question. How was the pKa derived?

Answer 1

pKa is the negative logarithm of acid dissociation constant(Ka). If the dissociation of an acid HA is as follows-

  HA → H+ + A-

Then, acid dissociation constant is expressed as –

  

K = [H+]A] [HA]

Where, […] indicates concentration at equilibrium.

Therefore, pKa is derived as –

  

pka = -log [H+][A-], [HA]

We can write the equation as,
  

pKa = -log(1421) – log [H*]

Again, we know,
– log(H+1=pH
. So,
  
TAV pka = – log в \НА). + pH

Or,
  

([A] pH = pKa + log [HA]

Now, the pKa value of aspirin is 3.5 and pH is of stomach is given to be 1. Putting the values in the equation, we can determine the ratio of acetylsalicylate ion to acetylsalicylic acid as follows –

Or,

[A ] 1 = 3.5 + log (HAJ)

Or.

log (121) = 1 – 3.5

Or,  

log (193) = -2.5

(14->) = 10-2.5 = 3.16 x 10-3 (HA/

Therefore, the ratio of acetylsalicylate ion to acetylsalicylic acid at pH=1 in the stomach is and it is less than one which implies that there is more acetylsalicylic acid at this pH.

3.16 X 10-3