The student made a mistake by asserting that hydrogen maintains a +1 oxidation state in both H2 and HI. In H2, the oxidation state of hydrogen is 0 because it is in its elemental form. When it forms HI, hydrogen indeed has an oxidation state of +1, while iodine, as the product HI, has an oxidation state of -1. Therefore, in this reaction, hydrogen is oxidized (from 0 to +1) and iodine is reduced (from 0 in I2 to -1 in HI). Because there are changes in oxidation states for both elements, this reaction is indeed a redox reaction.
H2(g) + I2(g) → 2HI(g)
A student makes the following statements:
Hydrogen always has the same oxidation number, so it has an oxidation number of +1 in both the reactant H2 and product HI.
Iodine is in Group VIIA, so it has an oxidation number of –1 in both the reactant I2 and product HI.
Neither hydrogen nor iodine changes oxidation states, so the reaction is not a redox reaction.
In three to five sentences, describe the mistake that the student made, and determine whether or not the reaction is a redox reaction. Explain your answer.
1 answer