Massachusetts Wastewater Practice Exam

What happens when cyanide solutions reach an acid pH?

1. Hydrogen cyanide is released.

2. pH increases.

3. Cyanide is reduced.

4. ORP is unchanged.

The correct answer is: Hydrogen cyanide is released.

When cyanide solutions reach an acid pH, hydrogen cyanide (HCN) is released. This process occurs because cyanide exists in different forms depending on the pH of the solution. At an alkaline pH, cyanide typically exists in a more stable ionic form, while in acidic conditions, it can convert to gaseous hydrogen cyanide. This transformation is critical in various environmental and safety contexts, particularly in wastewater management, as hydrogen cyanide is a highly toxic compound that poses significant health risks. Understanding this reaction is essential for those involved in managing wastewater containing cyanide or similar compounds, as it highlights the importance of monitoring pH levels to prevent the release of toxic gases. In practical applications, controlling the pH can be a vital step in treating cyanide waste effectively, ensuring that safety protocols are in place to mitigate risks associated with hydrogen cyanide exposure.