Question

How do you calculate the pH of \[a{\text{ }}0.050{\text{ }}M\] sodium cyanide solution?

Answer 1

Hint: The term cyanide refers to an independently charged anion comprising of one carbon atom and one nitrogen atom got together with a triple bond, \[C{N^ - }\] The most poisonous type of cyanide is free cyanide, which incorporates the cyanide anion itself and hydrogen cyanide, \[HCN\] , either in a gaseous or aqueous state.

Complete step by step answer:Cyanide is extremely reactive, forming straightforward salts with alkali earth cations and ionic complexes of differing qualities with various metal cations; the stability of these salts is subject to the cation and on\[pH\] . The salts of sodium, potassium, and calcium cyanide are very harmful, as they are exceptionally solvent in water, and thus readily dissolve to form free cyanide
Sodium cyanide is the base of hydrocyanic Acid, HCN. As a result, it experiences a hydrolysis response when added to water.
\[C{N^ - }\] \[ + \] \[{H_2}O{\text{ }} \to {\text{ }}HCN{\text{ }} + {\text{ }}O{H^ - }\;\;\;Kb{\text{ }} = {\text{ }}2 \times \times {10^{ - 5}}\]
Given in solution that is \[0.05{\text{ }}M\] \[NaCN\] , a little segment of it, x, will dissolve into equivalent parts of
HCN = x and OH- = x.
The equilibrium reaction will be: $\dfrac{{\left[ {{\text{HCN}}} \right]{{[{\text{OH}}]}^ - }}}{{C{N^ - }}}$ = $\dfrac{{\left| x \right|\left| x \right|}}{{|0.05MC{N^ - } - x}}$
To find the value of x:
x = 0.001 M \[HCN\] and OH−−
Based on this answer, the pH will be:
\[pH\] =\[\;14\] + \[log\left[ {{\text{ }}O{H^ - }} \right]\] = \[14\] + \[log\left[ {{\text{ }}0.001{\text{ }}M{\text{ }}O{H^ - }\;} \right]{\text{ }} = {\text{ }}11\]
This answer expected that the measure of dissociation of HCN is insignificant contrasted with its Concentration. On the off chance that you tackle this precisely you will get:
\[pH\] \[ = \] \[10.9956\] or about \[pH{\text{ }} = {\text{ }}11\] (approx)

Note:
The cyanide particle additionally combines with sulfur to form thiocyanate, SCN-. Thiocyanate dissociates under weakly acidic conditions, yet is normally not considered as a WAD animal category since it has comparable complexing properties to cyanide. Thiocyanate is roughly multiple times less toxic than hydrogen cyanide however is disturbing to the lungs, as thiocyanate synthetically and naturally oxidizes into carbonate, sulfate, and smelling salts.