this is about the reaction of aldehyde with HCN ..... so... why should the PH of the reaction be maintained or buffered between 6-8 ??
Thank You 
Too much of H
+, that is at a lower pH may cause the aldehyde to get oxidised to a carboxylic acid. This is why we need to keep the aldehyde in a nearly neutral medium.
If the pH is too high, the OH
- will react with H
+ from HCN such that no reaction will take place with the aldehyde which might as well be reduced by the huge amount of OH
-.
Hope it helps
