Use the chemical equation to complete the activity. 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. (4 points)
The mistake that the student made is assuming that hydrogen always has an oxidation number of +1 and iodine always has an oxidation number of -1. In reality, the oxidation number of an element can vary depending on the compound it is in. In the reactant H2, the oxidation number of hydrogen is 0, and in the product HI, the oxidation number of hydrogen is +1. Similarly, in the reactant I2, the oxidation number of iodine is 0, and in the product HI, the oxidation number of iodine is -1.
The reaction is indeed a redox reaction because the oxidation numbers of both hydrogen and iodine have changed during the reaction. Hydrogen has gone from an oxidation state of 0 to +1, indicating that it has been oxidized. Iodine has gone from an oxidation state of 0 to -1, indicating that it has been reduced. Therefore, the reaction involves both oxidation and reduction, making it a redox reaction.