The correct option is **C. Solubility increases as temperature increases.** ### Detailed Explanation 1. **Understanding Solubility**: - Solubility is defined as the maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature and pressure. For solid solutes in water, temperature plays a significant role in determining how much of the solute can dissolve. 2. **Effect of Temperature on Solubility**: - For most solid solutes, increasing the temperature generally increases their solubility in water. This is because higher temperatures provide more kinetic energy to the molecules involved. As the temperature rises, the water molecules move faster, which helps to break apart the solute particles more effectively and allows more of them to enter the solution. 3. **Thermodynamics of Dissolution**: - The process of dissolving a solid in a solvent can be understood through the lens of thermodynamics. When a solid dissolves, it typically requires energy to break the intermolecular forces holding the solid together (endothermic process). As temperature increases, the energy available in the system also increases, facilitating this process. - Additionally, the dissolution process often leads to an increase in entropy (disorder), which is thermodynamically favorable. The combination of these factors means that for most solids, higher temperatures lead to greater solubility. 4. **Examples**: - A common example is table salt (sodium chloride, NaCl). At room temperature, a certain amount of NaCl can dissolve in water. However, if you heat the water, you can dissolve a greater amount of NaCl before reaching saturation. - Another example is sugar (sucrose). When making sweetened beverages, heating the water allows more sugar to dissolve than if you were to add sugar to cold water. ### Why Other Options Are Incorrect - **A. Solubility decreases as temperature increases**: - This statement is generally false for solid solutes. While it may apply to some gases (where solubility decreases with increasing temperature), it does not hold true for most solids. - **B. Solubility remains constant regardless of temperature changes**: - This is incorrect because solubility is not a constant value; it varies with temperature. The relationship between temperature and solubility is well-documented and is a fundamental concept in chemistry. - **D. Solubility is only affected by pressure, not temperature**: - This statement is misleading. While pressure does affect the solubility of gases (where increased pressure can increase solubility), it is not the only factor. Temperature is a critical factor for solid solutes, and its effect cannot be ignored. ### Common Pitfalls - **Confusing Solubility of Gases vs. Solids**: Remember that while the solubility of gases typically decreases with increasing temperature, the opposite is true for most solid solutes. - **Ignoring the Role of Pressure**: While pressure has a significant effect on gas solubility, it has a negligible effect on the solubility of solids in liquids. ### Revision Summary - For most solid solutes, solubility increases with temperature. - Higher temperatures provide more kinetic energy, aiding the dissolution process. - The dissolution of solids is often endothermic and increases entropy, favoring solubility at higher temperatures. - Remember the distinction between the solubility behavior of solids and gases with respect to temperature changes.