In a buffer that is equal molar in acid and base components

In a buffer that is equal molar in acid and base components, will there be any difference in the amount of acid or base it can absorb before changing by one pH unit? Explain what you expect to see.

If a drop of acid is 1/20 of a mL describe how you could predict (calculate) the new pH that would be achieved when you add 1 drop of 0.3M acid to the 25 mL of water.

Solution

The quantity of a strong acid or base that must be added to change the pH of one litre solutionby one pH unit.

The buffer range is the pH range where a buffer effectively nutralises the added acids and bases while maintaining a relatively constant pH.

Ka = [H⁺] +[A^-] / [HA]

pH = pKa + log [A^-] / [HA]

where [A^-] - concentration of the cojugate base

  [HA]- concentration of the acid

when the ratio between the conjugate base and acid is equal to 1,then pH=Pka

If the ratio increases to a value of10,then the pH increases by 1 unit, since log(10)=1

The buffer capacity has a range of about 2.This means, when a buffer is created,the pH can be changed -1 by acid +1 by base before the pH begins to change.

pH = pKa + log [A^-] / [HA]

= 14+ log {[0.3]/[1.25]} Since Pka of water is 14

= 13.56