Discuss the function of a buffer. how will ph change when small amounts of acids or bases are added to the buffer solution?

Buffer solution is a blend that has the ability to prevent the pH of the solution from undergoing large variations. It is formed by a weak acid or base, and a salt of that acid or base.
Thus, the following species exist in this buffer solution:
 
H2CO3: present in great quantity, therefore, being a weak acid, it suffers little ionization;
H +: from the ionization of H2CO3;
HCO3-: also present in high quantity, from ionization of H2CO3 and dissociation of salt (NaHCO3);
Na +: from ionization of NaHCO 3;
If this solution is added a small concentration of acid, its ionization will occur, generating H + cations, which will react with the HCO3- anions present in the medium, giving rise to non-ionized carbonic acid. There is no change in pH.
If a base is added, OH- anions will be generated. These ions combine with the H + cations from the ionization of H2CO3. Thus, the OH- anions are neutralized, maintaining the pH of the medium.

To better understand the annex follows:

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