(a) A piece of magnesium ribbon is ignited and placed in a gas jar of oxygen.The equation for the reaction is 2Mg + O2 → 2MgO (i) Give two observations that would be made in this reaction. (2) 1 ................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................................................................................................................... 2 ................................................................................................................................................................................................................................................................................ ....................................................................................................................................................................................................................................................................................(ii) State why this is an oxidation reaction. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................(b) A second piece of magnesium ribbon is ignited and placed in a gas jar of carbon dioxide.A very exothermic reaction occurs, forming magnesium oxide and carbon.(i) State what is meant by the term exothermic. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................(ii) Give the chemical equation for this reaction. (1) ....................................................................................................................................................................................................................................................................................(iii) A fire starts in a warehouse where magnesium is stored.Suggest why it would not be suitable to use a carbon dioxide fire extinguisher to put out this fire.
Question
(a) A piece of magnesium ribbon is ignited and placed in a gas jar of oxygen.The equation for the reaction is 2Mg + O2 → 2MgO (i) Give two observations that would be made in this reaction. (2) 1 ................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................................................................................................................... 2 ................................................................................................................................................................................................................................................................................ ....................................................................................................................................................................................................................................................................................(ii) State why this is an oxidation reaction. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................(b) A second piece of magnesium ribbon is ignited and placed in a gas jar of carbon dioxide.A very exothermic reaction occurs, forming magnesium oxide and carbon.(i) State what is meant by the term exothermic. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................(ii) Give the chemical equation for this reaction. (1) ....................................................................................................................................................................................................................................................................................(iii) A fire starts in a warehouse where magnesium is stored.Suggest why it would not be suitable to use a carbon dioxide fire extinguisher to put out this fire.
Solution
(a) (i) Two observations that would be made in this reaction are:
- The magnesium ribbon would burn with a bright, white flame.
- A white ash (magnesium oxide) would be left after the reaction.
(ii) This is an oxidation reaction because the magnesium gains oxygen to form magnesium oxide.
(b) (i) The term exothermic refers to a reaction that releases energy in the form of heat.
(ii) The chemical equation for this reaction is: 2Mg + CO2 → 2MgO + C
(iii) It would not be suitable to use a carbon dioxide fire extinguisher to put out this fire because magnesium can react with carbon dioxide to produce magnesium oxide and carbon, which can further fuel the fire.
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