Your questions answered
If carrying this out as a class experiment the video advised reducing the scale but this is not included on the experiment sheet. What should I do?
You should use the small scale, as it significantly reduces amount of sulfur dioxide (toxic) being formed in the event of the sufur catching fire. Further updated practical details can be obtained here.
Remember it is the responsibility of the class teacher to carry out a risk assessment before doing any practical work in the classroom.
What should I do if the test tube does catch fire?
If, despite taking all precautions, the sulfur vapour does ignite, the students must be trained to extinguish it by placing a damp rag firmly over the mouth of the test tube. When introducing the practical activity, you should discuss all aspects of safety with the class.
How do I convince the students that a new substance has been formed?
Firstly get them to look for the signs that a chemical reaction is taking place. In this case the test tube will glow. Secondly the substance left in the test tube at the end of the reaction is black. Remind them that they started by mixing a yellow substance with a grey one. Ask them where the black substance came from? Finally, you could also ask them to test it with a magnet. The new iron sulfide will not separate out into iron and sufur when a magnet is applied.
Is iron (II) sufide magnetic? I am sure it was when I last tried this experiment.
Iron (II) sulfide is non-magnetic; however, sometimes the substance formed in this reaction shows magnetic properties. This is most likey due to the presence of some unreacted iron and you may need to explain this to the class. It is advisable to use a very weak magnet if doing this part of the activity!
What would be a good follow up to this next lesson?
You could re-enforce learning by extending this thinking to other reactions. For example, you could ask the students to predict what would happen if a mixture of zinc and sulfur was heated. Ask them draw some particle diagrams to support thier prediction.You could then demonstrate the reaction between zinc and sulfur (this was the second reaction shown on the video clip) and have a further discussion.