Question

The ratio for ( ionized /unionized ) for weak base
(Pka = 10.4 ) in blood (ph = 7.4)

Will be ??

Answer 1

How do you go from pKa to pH?

And if that is the only acid (or base) the solution contains, [H+] = [A-]. So only in such cases when that is the only acid and c is known, it is possible to "convert pKa to pH" by solving the quadratic equation Ka = [H+]^2/(c-[H+]) for H+ and then, of course, calculating pH = - log([H+]/mol dm^-3).

pH - Partition Theory

For a drug to cross a membrane barrier it must normally be soluble in the lipid material of the membrane to get into membrane and it has to be soluble in the aqueous phase as well to get out of the membrane. Many drugs have polar and non-polar characteristics or are weak acids or bases. For drugs which are weak acids or bases the pKa of the drug, the pH of the GI tract fluid and the pH of the blood stream will control the solubility of the drug and thereby the rate of absorption through the membranes lining the GI tract.

Brodie et al. (Shore, et al. 1957) proposed the pH - partition theory to explain the influence of GI pH and drug pKa on the extent of drug transfer or drug absorption. Brodie reasoned that when a drug is ionized it will not be able to get through the lipid membrane, but only when it is non ionized and therefore has a higher lipid solubility.

Brodie tested this theory by perfusing the stomach or intestine of rats, in situ, and injected the drug intravenously. He varied the concentration of drug in the GI tract until there was no net transfer of drug across the lining of the GI tract. He could then determined the ratio, D as:

D = Total concentration divided by       Total concentration in GI Tract

Key Takeaways: pKa Definition

The pKa value is one method used to indicate the strength of an acid. pKa is the negative log of the acid dissociation constant or Ka value. A lower pKa value indicates a stronger acid. That is, the lower value indicates the acid more fully dissociates in water

pKa formula: pKa is defined as -log10 Ka where Ka = [H+][A-] / [HA]. From these expressions it is possible to derive the Henderson-Hasselbalch equation which is. pKa = pH + log [HA] / [A-] This tells us that when the pH = pKa then log [HA] / [A-] = 0 therefore [HA] = [A-] ie equal amounts of the two forms.

The pKa of a drug is the hydrogen ion concentration (pH) at which 50% of the drug exists in its ionized hydrophilic form (i.e., in equilibrium with its un-ionized lipophilic form). All local anesthetic agents are weak bases. At physiologic pH, the lower the pKa the greater the lipophilicity.

The pKa is the pH value at which a chemical species will accept or donate a proton. The lower the pKa, the stronger the acid and the greater the ability to donate a proton in aqueous solution. The Henderson-Hasselbalch equation relates pKa and pH.

when the pH is equal to the pKa there are equal amounts of protonated and deprotonated forms of the acid. ... At a pH below the pKa, the acid is protonated. At a pH above the pKa the acid is deprotonated. If the pH equals the pKa, the acid is 50% protonated and 50% deprotonated

Lower the pKa value stronger the acid is. Higher pKa indicates weaker the acid. then its high value indicates a relatively strong base (weak conjugate acid).

A lower pKa means the Ka value is higher and a higher Ka value means the acid dissociates more readily because it has a larger concentration of Hydronium ions (H3O+).

001) = -3 so pKa = 3. So the higher the pKa the smaller Ka, and this means a weaker acid. ... If pKa indicates the pH in which a weak acid has the same concentration with its conjugate base, then what does the pKb of its conjugate base shows

Remember that when the pH is equal to the pKa value, the proportion of the conjugate base and conjugate acid are equal to each other. As the pH increases, the proportion of conjugate base increases and predominates. ... If the pH is at least 2.0 pH units below the pKa, then the conjugate acid is at least 99% of the total.

The lower the pH, the higher the concentration of hydrogen ions [H+]. The lower the pKa, the stronger the acid and the greater its ability to donate protons. pH depends on the concentration of the solution

Blood : Health problems that make your body too acidic or too alkaline are usually linked to the pH of blood. Changes in your normal blood pH might be a sign of certain health conditions and medical emergencies. These include: asthma.