We received a request from a Materials Engineering student for assistance on the proper handling of an electrolyte that contains sulfuric acid and potassium thiocyanate. This particular reaction will evolve hydrogen cyanid gas. The student plans to make 500 ml of the electrolyte. The student plans to use 66.6 ml of H2SO4 and 4.9 g of KSCN. The balance of the solution will be water. 

The current plan is to scrub the hydrogen cyanid gas that is generated during the reaction by bubbling it through NaOH. This practice was determine from wet scrubbing literature. 

The problem we are trying to solve concerns the handling of waste. I am concerned about the generation of HCN in the waste collection vessel which will pressurize the container. We obviously don’t want to use a vented cap. We are kicking around the idea of adding more sulfuric acid to the reaction vessel to force the reaction to completion by using up all the CN- ions. I don’t want to add NaOH to the reaction vessel because the reaction with Sulfuric acid is extremely violent. 

Is this approach reasonable?