Which step should be performed before adding a sample or solvent to a separatory funnel?

• A. Heat the funnel to 100 °C
• B. Ensure the stopcock is closed
• C. Add drying agent to the funnel
• D. Rinse the funnel with concentrated acid

Answer: (B)

Verified step by step guidance

1. Understand the purpose of a separatory funnel: it is used to separate immiscible liquids based on their densities.
2. Before adding any sample or solvent, it is crucial to prevent any liquid from leaking out through the stopcock.
3. Therefore, the first step is to ensure that the stopcock at the bottom of the separatory funnel is closed securely.
4. This prevents accidental spills and allows safe mixing and separation of the liquids inside the funnel.
5. Only after confirming the stopcock is closed should you proceed to add your sample or solvent.