Question

When CrO4- reacts to form CR⁽³⁺⁾, the chromium in CrO4- is?

1) reduced; it loses electrons
2) reduced; it loses oxygen
3) oxidized; its oxidation number increases
4) oxidized; it gains positive charge

Answer 1

The chromium in CrO4- is reduced, meaning it gains electrons, as it transitions from a +6 to a +3 oxidation state when forming Cr3+.

Step-by-step explanation:

When CrO4- reacts to form Cr3+, the chromium in CrO4- is reduced; it loses electrons. Reduction is defined as the gain of electrons or a decrease in oxidation state. In this particular reaction, the chromium atom is being reduced from a +6 oxidation state to a +3 oxidation state. This transition involves the chromium atom gaining electrons.

Let's clarify the entire redox process to understand this better: In redox reactions, oxidation refers to the loss of electrons, whereas reduction refers to the gain of electrons. When chromium goes from CrO4- to Cr3+, it must gain three electrons because its charge goes from a +6 oxidation state to a +3 oxidation state.

Therefore, when Chromium is reduced, it gains three electrons, and referring to the provided information when it changes from CrO3 (with an oxidation state of +5) to CrO4- (with an oxidation state of +7), it is being oxidized.

This is not the transformation the student is referring to, thus the accurate process as per the question is the reduction of chromium in the transition from CrO4- to Cr3+.