On Hydrocyanic Acid and Sodium Cyanide Buffer System
There is a buffer system composed of hydrocyanic acid and sodium cyanide, which is of great significance in chemical experiments and many fields.

Hydrocyanic acid ($HCN $), a weakly acidic substance, is partially ionized in water, and its ionization equilibrium formula is $HCN\ rightleftharpoons H ^ {+} + CN ^ {-} $. Sodium cyanide ($NaCN $), a strong electrolyte, is completely ionized in water, $NaCN = Na ^ {+} + CN ^{-}$。

The principle of action of this buffer system is based on the principle of equilibrium movement. When a small amount of acid is added to the system, the concentration of $H ^ {+} $increases, the equilibrium of $HCN\ rightleftharpoons H ^ {+} + CN ^ {-} $moves in the opposite direction, and $CN ^ {-} $binds $H ^ {+} $to generate $HCN $, thereby inhibiting the concentration of $H ^ {+} $to rise sharply, making the pH value of the solution relatively stable. If a small amount of alkali is added, $OH ^ {-} $reacts with $H ^ {+} $, the concentration of $H ^ {+} $decreases, and the equilibrium moves forward. $HCN $ionization supplements $H ^ {+} $to maintain the stability of $pH $.

To configure this buffer solution, accurately calculate the dosage of $HCN $and $NaCN $according to the required $pH $value and buffer capacity. According to the $Henderson-Hasselbalch $equation $pH = pK_ {a} +\ lg\ frac {[A ^{-}]}{[ HA]} $ ($pK_ {a} $of $HCN $is known, $[A ^ {-}] $is $CN ^ {-} $concentration, $[HA] $is $HCN $concentration), the ratio of the two can be easily calculated.

In practical applications, this buffer system is used in the electroplating industry, which can stabilize the pH value of the plating solution and improve the quality of the coating. In some chemical reactions, it can provide a suitable pH environment to ensure the smooth progress of the reaction.

However, it should be noted that both hydrogen cyanide and sodium cyanide are highly toxic, and strict safety procedures must be followed when using to prevent leakage and poisoning accidents. The operation should be carried out in a well-ventilated environment by professionals to ensure the safety of personnel and the environment is not polluted. In short, although the hydrogen cyanide and sodium cyanide buffer system has significant functions, the safety string should not be loosened when used.