Buffers And Neutralisation Flashcards
What is a buffer solution
A system that minimizes pH changes when small amounts of acid or a base is added
What are the 2 ways a buffer solution is made
Mix a weak acid and its salt (eg ethanoic acid and sodium Ethanoate)
Partially neutralize an excess of a weak acid using an Alkali
If extra acid is added how does pH remain the same
H+ increases
H+ reacts with A- (conjugate base) to produce HA
The equilibrium shifts left, removing most of the H+ ions, therefore H+ remains roughly constant and pH is relatively unaffected
If extra alkali is added how does pH remain the same
OH- increases
The H+ reacts with OH- to produce H2O which removes the OH- ions.
Equilibrium then shifts to right and HA dissociates to produce more H+
Hence H+ remains roughly constant and pH is relatively unaffected
What does the pH of a buffer solution depend on
Acid dissociation constant,Ka, of the weak acid present in the buffer
The conc ratio of weak acid and its conjugate base
What is the equation of Ka for a buffer solution
Ka= H+ X A- / HA
What is the equation of pH for a buffer solution
pH= pKa + log (salt form) / (acid form)
What it the equivalence point
The volume of one solution that exactly reacts with the volume of another solution
The center of the vertical section of the pH titration curve
Draw the dissociation curve for a:
Strong acid-strong base
Strong acid-weak base
Weak acid- strong base
Weak acid-weak base
Strong acid-strong base: start at bottom finishes at top
Strong acid-weak base: start at bottom finish middle/upper
Weak acid-strong base: start middle/bottom finish high
Weak acid-weak base: start middle/upper finish middle/ bottom
What makes a good indicator
Have a colour change which coincides with the vertical section of the pH titration curve.
Have the equivalence point within the equivalence point
