What is the outcome when a "mystery metal" replaces copper in the Reinsch test?

When a "mystery metal" replaces copper in the Reinsch test, the correct outcome is the formation of a dark film. The Reinsch test is a qualitative analysis technique primarily used to detect the presence of heavy metals, such as arsenic, antimony, and bismuth, in a solution. In this test, copper serves as a reducing agent, and when it interacts with these heavy metals, a distinctive reaction occurs.

If a different metal is used in place of copper, the formation of a dark film occurs due to the precipitation of metal or metal compounds. This dark film is typically composed of the reduced form of the heavy metal that reacts with the test solution. The visual cue of this dark film on the metal strip or electrode is indicative of a successful reaction with the unknown substance, confirming the presence of specific heavy metals.

Other outcomes such as color changes, gas emissions, or temperature increases are not characteristic results of the Reinsch test when using different metals. The dark film is the most definitive result that allows chemists to identify and confirm the presence of heavy metals in a sample.