Question

Zirconia, which is \(\mathrm{Zr} \mathrm{O}_{2}\), is used to make ceramic knives. What are the oxidation states of zirconium and oxygen in zirconia?

Short answer

The oxidation state of zirconium in zirconia is +4, and the oxidation state of each oxygen is -2.

Step-by-step solution

Identify Known Oxidation States

Recall that the oxidation state of oxygen in compounds is usually -2. There are two oxygen atoms, so the total oxidation for oxygen is -4.

Determine the Oxidation State of Zirconium

Zirconia is a neutral compound, which means the sum of the oxidation states must equal zero. If oxygen has a total of -4, zirconium must have an oxidation state of +4 to balance out the charge.

Verify the Sum of Oxidation States

Verify that the sum of the oxidation states equals zero: +4 (zirconium) + 2(-2) (oxygen) = +4 - 4 = 0. Since the sum is zero, the oxidation states are verified.

Key concepts

Zirconia

Zirconia, or zirconium dioxide (\textbf{ZrO\(_2\)}), is an advanced ceramic material with exceptional properties. Due to its high melting point, strength, and resistance to corrosion, zirconia is widely used for making diverse products, including ceramic knives, dental crowns, and as an insulator in oxygen sensors. It's important to observe that its impressive characteristics are a result of its chemical structure and the oxidation states of its constituent elements.

Zirconia exists in several different crystal structures, with the most stable form at room temperature being the monoclinic phase. However, under different temperature conditions, it can transition to tetragonal and cubic phases, which are important for various industrial applications. In the context of redox chemistry, zirconia plays a pivotal role in catalytic converters due to its ability to withstand redox reactions without altering its structure significantly.

Oxidation State of Zirconium

Understanding the oxidation state of zirconium in zirconia is key to grasping its chemical reactivity. In the compound \textbf{ZrO\(_2\)}, zirconium exhibits an oxidation state of +4. This is determined by considering the total charge of the compound and the common oxidation states of the elements involved. Since zirconia is neutral and oxygen typically has an oxidation state of -2, zirconium must balance this with a positive charge. This results in the general formula \textbf{Zr\(^{4+}\)(O\(^{2-})_2\)}.

The +4 oxidation state of zirconium is significant because it plays a crucial role in the stability and properties of zirconia. For example, the high oxidation state is responsible for zirconia's resistance to corrosion and heat, making it suitable for use in harsh environments. It is also important to note that while zirconium can exist in other oxidation states under different conditions, the +4 state is the most stable and common in zirconia.

Oxidation State of Oxygen

In chemical compounds, oxygen is known for its highly electronegative character and almost always has an oxidation state of -2. This holds true for zirconia (\textbf{ZrO\(_2\)}) as well, where each oxygen atom has an oxidation state of -2. Oxygen's preference for this oxidation state is due to its tendency to gain two electrons to fill its valence shell and achieve stability, mimicking the electronic configuration of the noble gas neon.

When teaching the concept of oxidation states, emphasizing oxygen's consistent -2 state is crucial because it lays a foundation for predicting oxidation states in more complex compounds. Whether dealing with simple oxides or elaborate organic molecules, students can frequently count on oxygen having this characteristic oxidation state, simplifying the process of balancing redox reactions.

Balancing Oxidation Numbers

Balancing oxidation numbers is a fundamental concept in chemistry that ensures the total charge in a chemical equation is conserved. When solving for oxidation states, it is imperative to understand that the sum of oxidation numbers for a neutral compound must be zero. In zirconia (\textbf{ZrO\(_2\)}), we determined that zirconium has an oxidation state of +4 and oxygen has an oxidation state of -2 per atom.

To verify the balance, we must multiply the oxidation state of oxygen by the number of oxygen atoms in the compound and then add it to the oxidation state of zirconium: \textbf{(+4) + 2(-2) = 0}, which satisfies the requirement for a neutral compound. Mastery of balancing oxidation numbers is not only useful for understanding individual compounds, like zirconia, but is also essential when dealing with more complex chemical reactions, particularly redox reactions which involve the transfer of electrons between species.