Video Transcript
Magnesium can be reacted with oxygen gas to make a magnesium oxide product. This reaction is described in the following chemical equation: two Mg solid plus O2 gas forms two MgO solid. Which of the following statements describes how the oxidation state of magnesium changes during this reaction? (A) It decreases from two to zero. (B) It increases from zero to one. (C) It decreases from one to zero. (D) It increases from one to two. Or (E) it increases from zero to two.
In this question, we want to determine what the oxidation state of magnesium is during the reaction with oxygen. It is customary to assign a negative oxidation number to the element with the higher electronegativity number and a positive oxidation number to the element with the lower electronegativity number.
If an atom is in its elemental form, its oxidation number is zero. Magnesium oxide is an ionic compound consisting of Mg2+ ions and O2− ions. For neutral magnesium to form a two plus ion, it needs to lose two electrons. The oxidation number tells us how many electrons have been removed in order to form the chemical bond. So two lost electrons means an oxidation number of plus two for the magnesium ion in MgO. As magnesium starts off in its elemental form, it must have an oxidation number of zero.
Thus, the statement that correctly describes how the oxidation state of magnesium changes during this reaction is (E): it increases from zero to two.
