Notice in the time-lapse video how magnesium metal displaces the copper in solution. In other words the magnesium metal dissolves and replaces the copper in solution which solidifies into copper metal and sinks to the bottom of the beaker.

Record your observations.

As the flame is brouight close to the reaction between the solution containing copper and the magnesium metal it glows with a green, blue colour. This is an indication of the presence of copper in the vapour produced by the reaction.
Review a lesson on flame testing

The gas given off in the displacement reaction above is very flammable as shown in the picture on the right.