Problem 135 - Chemistry An Atoms First Approach

Question

Will the following oxides give acidic, basic, or neutral solutions when dissolved in water? Write reactions to justify your answers. a. \(\mathrm{CaO}\) b. \(\mathrm{SO}_{2}\) c. \(\mathrm{Cl}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

In conclusion, CaO will give a basic solution when dissolved in water, as shown by the reaction: \(CaO (s) + H_{2}O (l) \rightarrow Ca(OH)_{2} (aq)\). Both SO₂ and Cl₂O will give acidic solutions when dissolved in water, as shown by the reactions: \(SO_{2}(g) + H_{2}O(l) \rightarrow H_{2}SO_{3}(aq)\) and \(Cl_{2}O (g) + H_{2}O (l) \rightarrow 2HClO (aq)\), respectively.

Step 1: a. CaO - Calcium oxide

Ca is a metal, and since the oxide of the metal gives a basic solution, CaO will give a basic solution when dissolved in water. The balanced chemical reaction is as follows: \[ CaO (s) + H_{2}O (l) \rightarrow Ca(OH)_{2} (aq) \] In this reaction, calcium oxide (CaO) reacts with water to produce calcium hydroxide (Ca(OH)₂), which is a strong base.

Step 2: b. SO₂ - Sulfur dioxide

S is a non-metal, so its oxide, SO₂, would give an acidic solution when dissolved in water. The balanced chemical reaction is as follows: \[ SO_{2}(g) + H_{2}O(l) \rightarrow H_{2}SO_{3}(aq) \] In this reaction, sulfur dioxide (SO₂) reacts with water to produce sulfurous acid (H₂SO₃), which is a weak acid.

Step 3: c. Cl₂O - Dichlorine monoxide

Cl is a non-metal, so its oxide, Cl₂O, would give an acidic solution when dissolved in water. The balanced chemical reaction is as follows: \[ Cl_{2}O (g) + H_{2}O (l) \rightarrow 2HClO (aq) \] In this reaction, dichlorine monoxide (Cl₂O) reacts with water to produce hypochlorous acid (HClO), which is a weak acid. In conclusion, we found that CaO will give a basic solution, while SO₂ and Cl₂O will give acidic solutions when dissolved in water.

Key Concepts

Acidic Solution

An acidic solution is formed when certain non-metal oxides react with water. These oxides, often derived from non-metals like sulfur or chlorine, become acids when hydrated.
When sulfur dioxide (SO_{2}) reacts with water, it forms sulfurous acid (H_{2}SO_{3}). This process can be summarized with the reaction: \[ SO_{2}(g) + H_{2}O(l) \rightarrow H_{2}SO_{3}(aq) \]
Similarly, dichlorine monoxide (Cl_{2}O) reacts with water to form hypochlorous acid, exhibited in the equation: \[ Cl_{2}O (g) + H_{2}O (l) \rightarrow 2HClO (aq) \]
Both sulfur dioxide and dichlorine monoxide, when interacting with water, demonstrate how non-metal oxides lead to acidic solutions. Acidic solutions have several properties:

• They have a pH less than 7.
• Often characterized by a sour taste.
• Color change of indicators like litmus paper from blue to red.

Understanding these reactions helps to predict the behavior of such oxides in nature and their role in phenomena like acid rain.

Basic Solution

Basic solutions arise when metal oxides, especially those from alkali and alkaline earth metals, react with water. In our example, calcium oxide (CaO) is such an oxide. When CaO dissolves in water, it produces calcium hydroxide (Ca(OH)_{2}), a compound that increases the concentration of hydroxide ions (OH^{-}) in solution.
The balanced chemical equation for this reaction is: \[ CaO (s) + H_{2}O (l) \rightarrow Ca(OH)_{2} (aq) \]
Basic solutions have distinctive properties such as:

• They have a pH greater than 7.
• Possess a slippery feel to the touch, due to the saponification of oils.
• Turn red litmus paper blue, indicating basicity.

Such reactions underscore the important concept that metal oxides typically yield basic solutions when in contact with water.

Chemical Reactions

Chemical reactions are the transformative processes where substances interact to form new compounds. These reactions are often classified by the types of reactants and products involved. In our context, we dealt with reactions involving oxides and water:

• Synthesis Reaction: Occurs when two or more reactants combine to form a single product. An example is the formation of calcium hydroxide from calcium oxide and water.
• Acid-Base Reaction: Characterized by the formation of water and a salt when an acid and a base interact. Although not directly showcased in this exercise, understanding the acidic and basic products connects to this reaction type.
• Decomposition Reaction: The opposite of a synthesis reaction, it involves breaking down compounds into simpler substances. For instance, the reverse decomposition of water into hydrogen and oxygen.

Chemical reactions are influenced by conditions such as the presence of water, temperature, and concentration. Understanding these factors is crucial in predicting and managing the behaviors of various chemical processes.