Problem 60 - Chemistry: The Central Science in SI Units, Global Edition

Question

Some metal oxides, such as \(\mathrm{Sc}_{2} \mathrm{O}_{3},\) do not react with pure water, but they do react when the solution becomes either acidic or basic. Do you expect \(\mathrm{Sc}_{2} \mathrm{O}_{3}\) to react when the solution becomes acidic or when it becomes basic? Write a balinced chemical equation to support vour answer.

Step-by-Step Solution

Answer

Sc2O3, scandium oxide, is an amphoteric metal oxide and reacts in both acidic and basic solutions. In an acidic solution like HCl, the reaction is \(Sc_2O_3 + 6HCl \to 2ScCl_3 + 3H_2O\), forming scandium chloride and water. In a basic solution like NaOH, the reaction is \(Sc_2O_3 + 6NaOH \to 2Na_3ScO_3 + 3H_2O\), forming sodium scandate and water.

Step 1: Identify the type of oxide

Sc2O3 is a metal oxide, specifically for scandium (Sc). Metal oxides typically are basic or amphoteric. For scandium, which is a periodic table group 3 metal, the oxide is expected to be amphoteric.

Step 2: Determine the type of reaction in each type of solution

Since scandium oxide (Sc2O3) is amphoteric, it can react with both acids and bases. When an amphoteric oxide reacts with an acid, the products are a salt and water. In contrast, when an amphoteric oxide reacts with a base, the products are also a salt and water.

Step 3: Write the balanced chemical equation for reaction with an acid

Let's use HCl as our acidic solution for the example. The balanced equation would be: \(Sc_2O_3 + 6HCl \to 2ScCl_3 + 3H_2O\) In this case, Sc2O3 reacts with hydrochloric acid (HCl) to form scandium chloride (ScCl3) and water.

Step 4: Write the balanced chemical equation for reaction with a base

Let's use NaOH as our basic solution for the example. The balanced equation would be: \(Sc_2O_3 + 6NaOH \to 2Na_3ScO_3 + 3H_2O\) In this case, Sc2O3 reacts with sodium hydroxide (NaOH) to form sodium scandate (Na3ScO3) and water.

Step 5: Conclusion

Sc2O3, scandium oxide, is an amphoteric metal oxide which means it reacts in both acidic and basic solutions. In an acidic solution, such as with HCl, it forms scandium chloride and water. In a basic solution, such as with NaOH, it forms sodium scandate and water.

Key Concepts

Metal Oxides

Metal oxides are compounds composed of metal elements combined with oxygen. These oxides can be classified into different types based on their reaction behavior. Generally, metal oxides are either acidic, basic, or amphoteric. The chemical nature of metal oxides depends on the metal they are derived from and its position in the periodic table.
For example:

• Basic oxides: Metals like sodium and calcium form basic oxides. These typically react with acids to form salts and water.
• Amphoteric oxides: Metals such as aluminum and zinc produce amphoteric oxides. These can engage in reactions with both acids and bases.
• Acidic oxides: Non-metals and some metal oxides behave as acidic, reacting with bases. However, metal oxides like scandium oxide (\(\mathrm{Sc}_{2} \mathrm{O}_{3}\)) are amphoteric, which means they can react with both acids and bases.

The amphoteric nature of metal oxides makes them quite interesting, as they exhibit dual characteristics, contributing to their versatile application in chemical processes.

Chemical Reactions

Chemical reactions are processes that involve the transformation of substances through the breaking and forming of chemical bonds. When we refer to the reactions of amphoteric metal oxides, like \(\mathrm{Sc}_{2} \mathrm{O}_{3}\), we observe their unique ability to react both as acids and bases under different conditions.
While basic metal oxides react straightforwardly with acids, and acidic oxides react with bases, amphoteric oxides show flexible behavior:

• In acidic conditions, amphoteric oxides act as bases, producing salts and water.
• In basic conditions, these oxides act as acids, also resulting in salts and water.

This dual reactive nature is guided by the conditions of the environment, specifically the acidity or alkalinity of the solution involved. Understanding these reaction properties allows chemists to utilize amphoteric oxides in a variety of applications, such as neutralizing certain types of solutes in mixtures.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They depict the reactants consumed and the products formed in the reaction. In a balanced chemical equation, the number of atoms for each element is the same on both sides of the equation, reflecting the law of conservation of mass.
When writing equations for amphoteric oxides like \(\mathrm{Sc}_{2} \mathrm{O}_{3}\):

• Reaction with an acid (e.g., \(\mathrm{HCl}\)): \(\mathrm{Sc}_{2} \mathrm{O}_{3} + 6\mathrm{HCl} \to 2\mathrm{ScCl}_{3} + 3\mathrm{H}_{2}\mathrm{O}\)
• Reaction with a base (e.g., \(\mathrm{NaOH}\)): \(\mathrm{Sc}_{2} \mathrm{O}_{3} + 6\mathrm{NaOH} \to 2\mathrm{Na}_{3} \mathrm{ScO}_{3} + 3\mathrm{H}_{2}\mathrm{O}\)

Such equations not only illustrate the reactants and products but also provide insight into the stoichiometry of the reactions. This understanding is crucial when predicting and calculating the outcomes of chemical reactions, whether in a laboratory setting or in industrial applications.