Buffers and Neutralisation Flashcards
Buffer solution
A system that minimises pH changes on additions of small amounts of an acid or base
How to make acidic buffers?
Weak acid and its salt (conjugate base)
CH3COOH/CH3COONa
Another way of forming a buffer
Excess weak acid and strong alkali e.g CH3COOH/NaOH
Role of CH3COOH/CH3COO- when adding acid to a buffer
H+ reacts with CH3COO- and equilibrium shifts to left to minimise change
Role of CH3COOH/CH3COO- when adding base to buffer
A- reacts with H+, H+ conc is lowered so equilibrium shift to the right because CH3COOH dissociates to replace lost H+ ions.
Buffer calculations
[H+] = Ka[Acid]/Salt (kasidova salt)
How is blood pH maintained by the carbonic acid-hydrogencarbonate buffer when acid is added
- H+ conc increases
- H+ aq ions react with HCO3-
- Equilibrium shift to left removing H+ ions
How is blood pH maintained by the carbonic acid-hydrogencarbonate buffer when alkali is added
- OH- conc increases
- Small conc of H+ ions react with OH-
- H2CO3 dissociates shifting equilibrium to right to restore lost H+ ions
Carbonic acid- hydrogencarbonate buffer
H2CO3 (foward/backward) H+(aq) + HCO3-(aq)
Equivalence point
Volume at which exactly the same number of moles of H+ has reacts as much as OH-
End point
Volume of acid or alkali added when solution changes colour
When do indicators change colour
Changes colour at equivalence point, pH range needs to lie within the centre of vertical section
