Problem 41 - Chemistry The Molecular Nature of Matter

Question

$$ \begin{aligned} &\text { What acid is formed when the following oxides react }\\\ &\text { with water? (a) } \mathrm{SO}_{3} \text { (b) } \mathrm{CO}_{2} \text { (c) } \mathrm{P}_{4} \mathrm{O}_{10} \end{aligned} $$

Step-by-Step Solution

Answer

When reacted with water, (a) \(\mathrm{SO}_{3}\) forms sulfuric acid (\(\mathrm{H}_{2}\mathrm{SO}_{4}\)), (b) \(\mathrm{CO}_{2}\) forms carbonic acid (\(\mathrm{H}_{2}\mathrm{CO}_{3}\)), and (c) \(\mathrm{P}_{4}\mathrm{O}_{10}\) forms phosphoric acid (\(\mathrm{H}_{3}\mathrm{PO}_{4}\)).

Step 1: Identify the Type of Reactions

The reactions of non-metal oxides with water typically form acids. This type of reaction is a synthesis reaction where the oxide reacts with water to form an acid.

Step 2: Write the Balanced Chemical Equations for Each Oxide

For each non-metal oxide given, we write a balanced chemical equation with water to form the corresponding acid.\(\mathrm{SO}_{3} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{2}\mathrm{SO}_{4}\) for sulfur trioxide.\(\mathrm{CO}_{2} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{2}\mathrm{CO}_{3}\) for carbon dioxide.\(\mathrm{P}_{4}\mathrm{O}_{10} + 6\mathrm{H}_{2}\mathrm{O} \longrightarrow 4\mathrm{H}_{3}\mathrm{PO}_{4}\) for tetraphosphorus decoxide.

Step 3: Determine the Resulting Acids

From the balanced equations, we can see that:\(\mathrm{SO}_{3}\) reacts with water to form sulfuric acid \(\mathrm{H}_{2}\mathrm{SO}_{4}\).\(\mathrm{CO}_{2}\) reacts with water to form carbonic acid \(\mathrm{H}_{2}\mathrm{CO}_{3}\).\(\mathrm{P}_{4}\mathrm{O}_{10}\) reacts with water to form phosphoric acid \(\mathrm{H}_{3}\mathrm{PO}_{4}\).

Key Concepts

Synthesis Reaction

Synthesis reactions are chemical processes in which two or more simple substances combine to form a more complex product. This type of reaction is integral to the formation of many compounds, including the acids students often encounter in chemistry. In the case of non-metal oxides reacting with water, the synthesis reaction leads to the production of an acid. For instance, when sulfur trioxide (\text{SO}\(_{3}\)) combines with water, it forms sulfuric acid (\text{H}\(_{2}\)\text{SO}\(_{4}\)), showcasing a classic example of a synthesis reaction in action. Each synthesis reaction is characterized by its simplicity - always look for two or more reactants forming a single product.

Balanced Chemical Equations

Balanced chemical equations are vital in representing chemical reactions accurately. They ensure the law of conservation of mass is adhered to, meaning the amount of each element is the same in both the reactants and products. A balanced equation has the same number of atoms of each element on both sides of the reaction arrow. For instance, in the reaction between carbon dioxide (\text{CO}\(_{2}\)) and water, we write \text{CO}\(_{2}\) + \text{H}\(_{2}\)\text{O} → \text{H}\(_{2}\)\text{CO}\(_{3}\) to denote the formation of carbonic acid, with the reactants and products having equal numbers of carbon, hydrogen, and oxygen atoms. Remember, balancing equations is like solving a puzzle, ensuring what you 'put in' is exactly what you 'get out' in terms of atoms.

Sulfuric Acid

Sulfuric acid (\text{H}\(_{2}\)\text{SO}\(_{4}\)) is a strong acid and a notable product of the synthesis reaction between sulfur trioxide and water. It's known for its wide range of applications, from fertilizer manufacturing to oil refining and chemical synthesis. The balanced chemical equation for its formation is a straightforward representation of a synthesis reaction: \text{SO}\(_{3}\) + \text{H}\(_{2}\)\text{O} → \text{H}\(_{2}\)\text{SO}\(_{4}\). When learning about sulfuric acid, it’s important to understand its strong acid properties and its significant role in both industrial and laboratory settings.

Carbonic Acid

Carbonic acid (\text{H}\(_{2}\)\text{CO}\(_{3}\)) forms when carbon dioxide gas dissolves in water and reacts through a synthesis reaction. \text{CO}\(_{2}\) + \text{H}\(_{2}\)\text{O} → \text{H}\(_{2}\)\text{CO}\(_{3}\). Although it is a weak acid, carbonic acid plays an essential role in the carbon cycle and helps regulate the pH of blood in our body. It is also the cause of the fizz in carbonated beverages, as it forms from dissolved \text{CO}\(_{2}\) and breaks down into water and carbon dioxide when the pressure is released.

Phosphoric Acid

Phosphoric acid (\text{H}\(_{3}\)\text{PO}\(_{4}\)) is typically formed through the synthesis reaction between tetraphosphorus decoxide (\text{P}\(_{4}\)\text{O}\(_{10}\)) and water. The balanced chemical equation, \text{P}\(_{4}\)\text{O}\(_{10}\) + 6\text{H}\(_{2}\)\text{O} → 4\text{H}\(_{3}\)\text{PO}\(_{4}\), illustrates the stoichiometry involved in this reaction. Phosphoric acid is considered a weak acid with three ionizable hydrogens and finds its use in food flavoring, rust inhibitors, and dental cements. Students can observe the step-wise ionization of this acid, which makes it an excellent subject when studying acids and their behavior.