Problem 106 - Chemistry and Chemical Reactivity

Question

Which of the following barium salts should dissolve in a strong acid such as HCl: \(\mathrm{Ba}(\mathrm{OH})_{2}, \mathrm{BaSO}_{4},\) or \(\mathrm{BaCO}_{3} ?\)

Step-by-Step Solution

Answer

Ba(OH)₂ and BaCO₃ dissolve in HCl, but BaSO₄ does not.

Step 1: Identifying Potential Reactions

To determine which barium salts would dissolve in a strong acid like HCl, we need to consider how these compounds would react with HCl. Substances that contain basic anions that react with H⁺ ions will dissolve in the acid.

Step 2: Assessing Basicity of Anions

Examine the anions present in each barium salt: - Ba(OH)₂ contains OH⁻ ions, which readily react with H⁺ ions to form water. - BaSO₄ contains SO₄²⁻ ions, which are not basic ions and do not react with H⁺ ions under normal conditions. - BaCO₃ contains CO₃²⁻ ions, which react with H⁺ ions to form H₂CO₃, which decomposes into CO₂ and water.

Step 3: Reaction Outcomes

Considering possible reactions: - Ba(OH)₂ + 2HCl → BaCl₂ + 2H₂O. This dissolves because OH⁻ reacts with H⁺. - BaSO₄ + HCl → No significant reaction occurs, so it remains largely insoluble. - BaCO₃ + 2HCl → BaCl₂ + CO₂ + H₂O. This dissolves because CO₃²⁻ reacts with H⁺ ions.

Step 4: Conclusion on Solubility

Based on the reactions, Ba(OH)₂ and BaCO₃ are able to dissolve when reacted with HCl because they contain basic anions that react with the acid. BaSO₄ does not dissolve significantly as its anion is not basic and does not react with H⁺ ions.

Key Concepts

Acid-Base Reaction

An acid-base reaction is a chemical process where an acid and a base interact. Strong acids like hydrochloric acid (HCl) are capable of donating protons (H⁺ ions) readily. Bases, on the other hand, can accept these protons. In the context of dissolving barium salts in HCl, we consider whether the anions in the salts can behave as a base.

• For instance, hydroxide (OH⁻) ions in barium hydroxide, \ \( \mathrm{Ba} (\mathrm{OH})_{2} \ \), accept H⁺ ions to form water.
• Similarly, carbonate (CO₃²⁻) ions in barium carbonate, \ \( \mathrm{BaCO}_{3} \ \), react with H⁺ ions to produce carbonic acid, \ \( \mathrm{H}_2\mathrm{CO}_3 \ \), which then decomposes to carbon dioxide and water.
• Barium sulfate, \ \( \mathrm{BaSO}_{4} \ \), however, contains sulfate ions (SO₄²⁻) that typically do not participate in acid-base reactions with strong acids.

Understanding this allows us to predict which barium salts might dissolve in a strong acid environment, based on active participation in an acid-base reaction.

Anion Basicity

Anion basicity refers to an anion's ability to accept protons (H⁺ ions) and participate in a reaction with acids. The basicity of an anion is crucial in understanding why some barium salts dissolve in hydrochloric acid (HCl), while others do not.

• In \ \( \mathrm{Ba(OH)}_2 \ \), the OH⁻ anion is a strong base, readily reacting with H⁺ to form water, which facilitates dissolution.
• In \ \( \mathrm{BaCO}_{3} \ \), the CO₃²⁻ anion is also basic. It reacts with H⁺ ions, eventually leading to the release of CO₂ gas and water, making the salt soluble in acid.
• On the other hand, SO₄²⁻ in \ \( \mathrm{BaSO}_{4} \ \) lacks basicity for meaningful reaction with H⁺, rendering it largely insoluble in HCl.

Thus, analyzing the basicity of anions helps predict solubility trends of various salts in strong acids.

HCl Reaction

Reactions with hydrochloric acid (HCl) involve the interaction of its H⁺ ions with anions in compounds. Whether a barium salt dissolves in HCl depends heavily on this interaction.

• Hydrochloric acid can effectively dissolve compounds containing anions that react to lower the free energy of the system, often via gas production or forming neutral molecules like water.
• For \ \( \mathrm{Ba(OH)}_2 \ \), the reaction with HCl produces barium chloride (BaCl₂) and water, facilitating dissolution.
• Similarly, \ \( \mathrm{BaCO}_{3} \ \) reacts with HCl to yield barium chloride, carbon dioxide (escaping as a gas), and water.
• In contrast, \ \( \mathrm{BaSO}_{4} \ \) remains unchanged because sulfate ions do not efficiently bind with H⁺ ions.

By assessing the likely outcomes of HCl reactions, one can determine the extent to which each barium salt will dissolve in such an acidic environment.