I hope the following information helps to address both questions.
Burning Magnesium ribbon in a Bunsen flame:
The flare from most chemicals burned in a Bunsen flame is usually of short duration and therefore is unlikely to pose any real hazard. The exception is burning magnesium ribbon, which burns with a light of high intensity and heat. Watching a magnesium fire can cause eye damage.
Burning small pieces of magnesium ribbon held with tongs over a Bunsen flame is recommended to only be done as a teacher DEMONSTRATION not as a class activity—a site-specific risk assessment should be carried out and safety procedures and guidelines followed as detailed below:
- Be aware that burning magnesium produces a lot of heat and a white flame that emits ultraviolet light.
- Wear safety glasses.
- The piece of magnesium ribbon should be no more than 2cm in length.
- Use crucible tongs to hold the piece of magnesium ribbon over the Bunsen burner flame to light it, or suspend the strip of magnesium over the Bunsen burner flame using a laboratory stand and clamp.
- Students should sit no closer than 2–3 m from the flame.
- Students are instructed NOT to look or stare directly at the burning metal, observation should be from the side (i.e., using peripheral vision) due to the risk of eye damage.
- Avoid breathing in the smoke from the burning magnesium ribbon.
- The following information is from the ChemSupply SDS:
- Highly flammable in the presence of open flames and sparks, or heat
- Flammable solid. Contact with moisture or water liberates flammable gases
- Ignites readily, burns with intense white light and heat
- Watching a magnesium fire can cause eye injury
The burning of magnesium is a reaction between the metal magnesium and oxygen in the air. A chemical change occurs forming a new compound: magnesium oxide.
See the following Youtube link demonstrating magnesium reacting with oxygen. https://www.youtube.com/watch?v=m2i9jLPXprQ
Burning of magnesium ribbon in a crucible:
This is a different activity. It is recommended as a class activity, provided a site-specific risk assessment is carried out and the following safety procedures and guidelines are followed:
- Wear safety glasses.
- The magnsium ribbon can be cut into about 15cm lengths before the lesson.
- The reaction is highly exothermic. Particular care should be taken to avoid burns.
- Students must only move the crucible and lid using tongs.
- Students should be discouraged from looking at the magnesium when it is burning and the bright light produced as this can cause eye damage.
- The number of magnesium strips used by students should be limited by the teacher.
This activity is a good way for senior students to demonstrate a combination/oxidation reaction and the conservation of mass in a chemical reaction.
- Take a piece of magnesium ribbon about 15 cm long and roll it into a tight coil.
- Weigh an empty crucible with lid and record its mass.
- Place the coil of magnesium ribbon into the crucible, weigh the crucible, lid and magnesium and record this mass.
- Place the crucible on a pipe clay triangle on a tripod stand and heat over a bunsen burner.
- Heat for 1 minute, then carefully lift the lid slightly with tongs. The magnesium will burst into flames as the air reaches it. Do not let any white smoke escape and replace the lid. This will prevent any loss of product (magnesium oxide).
- Lift the lid periodically over 5 minutes to ensure an adequate supply of oxygen.
- Let the crucible cool. When it is cool, weigh it. Record the mass of the crucible, lid and magnesium oxide. (Take care that a hot crucible is not placed on a plastic pan top of the balance or the plastic may melt.)
See Youtube video demonstrating magnesium reacting with oxygen in a crucible. https://www.youtube.com/watch?v=OuFqtxZJRvM
Ahlers, C. (2011). Expose, excite, ignite an essential guide to whizz-bang chemistry. Geelong West, VIC: Prof Bunsen Science Publishers.
Cash, S. (2012). Oxford big ideas. Science 8: Australian curriculum (1st Ed.).South Melbourne, VIC: Oxford University Press
Cash, S. (2012). Oxford big ideas. Science 10: Australian curriculum (1st Ed.).South Melbourne, VIC: Oxford University Press
Chem-supply. 2011. Safety Data Sheet: Magnesium Ribbon. https://www.chemsupply.com.au/documents/MT0321CHJN.pdf
Risk Assess; www.riskassess.com.au
Simpson, G. (2000). Heinemann Science Links 3. Port Melbourne, VIC: Reed International Books Australia Pty Ltd.