A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light.

Question

(i) A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write the balanced chemical equation when X is dissolved in water.
(ii) Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Answer 1

(i) 2Mg + O₂→ 2MgO + Light
3Mg + N₂→ Mg₃N₂
(a) X is MgO; Y is Mg₃N₂
(b) MgO + H₂O→ Mg(OH)₂

(ii) Grapes when attached to the plants are living and therefore, their own immune system prevents fermentation. The microbes can grow in the plucked grapes and under anaerobic conditions these can be fermented. This is a chemical change.