Buffer solutions are solutions that resist changes in pH on addition of an acid or a base.


Buffer solutions are made from a mixture of

  • A weak acid and its conjugate base. eg. Acetic acid and sodium acetate.


  • A weak base and its conjugate acid. eg. Ammonia and ammonium chloride.

The amount of acid and base are roughly in equal concentrations.

Natural buffers

The hydrogen carbonate buffer (H2CO3/ HCO3-) is an example of a natural buffer.

It keeps the pH of blood relatively constant around 7.4.

The buffer is made from the weak acid H2CO3(aq) and its conjugate base, the hydrogen carbonate ion, HCO3-(aq).

If the pH of blood falls outside the range of 6.8 to 7.8 death occurs. 


Excess acid in the blood is neutralised by the hydrogen carbonate ion

H+ (aq) + HCO3-(aq) ← → H2CO3(aq)


Excess base in the blood is neutralised by carbonic acid

H2CO3(aq) + OH-(aq) ← → HCO3-(aq) + H2O(l)


The levels of the carbonic acid in the blood are monitored by the brain which controls the rate of breathing.

H2O(l) + CO2(g) ← → H2CO3(aq)


Molar Mass

Formula Calculator