Question

The three common chromium oxides are \(\mathrm{CrO}\) \(\mathrm{Cr}_{2} \mathrm{O}_{3},\) and \(\mathrm{CrO}_{3} .\) If \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) is amphoteric, what \(\mathrm{can}\) you say about the acid-base properties of \(\mathrm{CrO}\) and \(\mathrm{CrO}_{3} ?\)

Short answer

The oxide \( \mathrm{CrO} \) is likely to be basic due to the low oxidation state of Chromium. In contrast, the \( \mathrm{CrO}_3 \) is most likely to be acidic due to the higher oxidation state of Chromium.

Step-by-step solution

Identify The Oxidation States

Identify the oxidation states of Chromium in the oxides, \( \mathrm{CrO} \), \( \mathrm{Cr}_2\mathrm{O}_3 \) and \( \mathrm{CrO}_3 \). In \( \mathrm{CrO} \), Chromium has an oxidation state of +2. In \( \mathrm{Cr}_2\mathrm{O}_3 \), Chromium has an oxidation state of +3. Lastly in \( \mathrm{CrO}_3 \), Chromium has an oxidation state of +6.

Understand the nature of oxides

Understand that metallic oxides and those of nonmetals behave differently. Metallic oxides tend to be basic, whereas nonmetal oxides are often acidic. Oxides of elements that can behave as both metals and nonmetals, like Chromium, can have either acidic, basic, or amphoteric behavior depending on their oxidation states.

Assign Acid-Base Characteristics

Assign acid-base characteristics based on the oxidation state of Chromium. The +2 state as in \( \mathrm{CrO} \) is more metallic and hence the oxide tends to be basic. The +6 state as in \( \mathrm{CrO}_3 \) is more nonmetallic and hence the oxide is more likely to be acidic. The +3 state of \( \mathrm{Cr}_2\mathrm{O}_3 \) as given is amphoteric.

Key concepts

Oxidation States of Chromium

The concept of oxidation states is fundamental when studying the properties of elements and their compounds. For chromium, a versatile element found in various oxidation states, its compounds exhibit distinct characteristics that are directly influenced by these states.
Chromium can exist in several different oxidation states, with +2, +3, and +6 being the most common in its oxides. It's crucial to remember that the lower oxidation states are typically associated with a more metallic character, while higher oxidation states are linked to more nonmetallic properties.

• In chromium(II) oxide (CrO), chromium is in the +2 oxidation state, making it more basic in nature.
• Chromium(III) oxide (Cr₂O₃) has chromium in the +3 state which exhibits amphoteric behavior, meaning it can react with both acids and bases.
• Finally, in chromium(VI) oxide (CrO₃), with chromium in the +6 state, the oxide shows acidic tendencies.

Understanding these oxidation states allows us to predict the chemical properties of chromium oxides, including their acid-base behavior.

Chemical Properties of Oxides

Diving into the chemical properties of oxides can give us insight into their reactions with acid and base compounds. Oxides can generally be categorized into basic, acidic, and neutral. However, an intriguing category includes oxides which are amphoteric, which means they can react with both acids and bases.

• Basic oxides, generally formed by metals, react with acids to produce salt and water.
• Acidic oxides, usually derived from nonmetals, react with bases to form salts and water as well.
• Neutral oxides show minimal reactivity towards acids or bases.
• Amphoteric oxides, like Chromium(III) oxide, react with both acids and bases, showcasing dual behavior.

The chemical behavior of an oxide depends on the element's electronegativity and the oxidation state. A higher oxidation state as seen in CrO₃ usually leads to acidic oxides, while lower oxidation states often result in basic oxides, like CrO.

Amphoteric Compounds

Amphoterism is a characteristic of a select group of compounds, which can act as both acids and bases. They adapt their behavior depending on the reacting substance.
Chromium(III) oxide (Cr₂O₃) is an example of an amphoteric oxide. It can react with acids to form chromium salts and water, demonstrating its basic side. Conversely, when it reacts with bases, it forms chromates or dichromates, thus behaving as an acid.

Examples in Reactions:

• With a strong acid: \[ Cr_2O_3 + 6HCl \rightarrow 2CrCl_3 + 3H_2O \]
• With a strong base: \[ Cr_2O_3 + 2NaOH + 3H_2O \rightarrow 2Na[Cr(OH)_4] \]

The ability of amphoteric compounds to react with a variety of chemicals makes them quite unique and versatile in the field of chemistry. This dual nature is determined by the compound's chemical structure and the presence of both acid and base functionalities.