Recording-2025-03-01T15:30:42.229Z

Temperature Effects on Aqueous Solutions

General Observations

• Dissolving Solid Substances:

  • Common experience suggests that solubility increases with temperature.

  • However, this is not universally applicable; the solubility of some solids can decrease with rising temperatures.

Solubility Behavior

• Dissolving Solids:

  • Higher temperatures lead to faster dissolving rates for solids.

  • Amounts of solid that can be dissolved may vary with temperature changes, which is shown in Figure 11.6.

• Notable Exceptions:

  • Sodium sulfate and cerium sulfate exhibit decreased solubility with increased temperature.

  • Although most solids are more soluble at higher temperatures, there are exceptions.

  • Predicting solubility’s dependence on temperature can be complex; experimentation is often necessary to understand specific solid behavior.

Gases in Aqueous Solutions

• Gas Solubility Trends:

  • Typically, gas solubility in water decreases with increasing temperature (illustrated in Figure 11.17).

  • This behavior carries significant environmental implications, especially concerning thermal pollution from industrial practices.

Environmental Implications

• Thermal Pollution:

  • Water returned to natural sources post-industrial use is at higher temperatures than the ambient environment.

  • This warmer water holds less oxygen and is less dense, leading to the formation of a warm upper layer that can inhibit oxygen absorption from the atmosphere.

  • This effect can adversely impact aquatic life in cooler, deeper water layers of lakes.

Boiler Scale Formation

• Chemical Reactions Involved:

  • Dissolved carbon dioxide forms bicarbonate ions in water:

    • CO₃²⁻(aq) + CO₂(aq) + H₂O(l) ⇌ 2 HCO₃⁻(aq)

  • When water containing calcium ions (Ca²⁺) is heated, the loss of carbon dioxide drives the reverse reaction:

    • 2 HCO₃⁻(aq) ⇌ Ca²⁺(aq) + H₂O(l) + CO₂(aq) + CO₃²⁻(aq)

  • This process can increase carbonate ion concentration, leading to the formation of insoluble calcium carbonate (CaCO₃).

  • The resulting solid, known as boiler scale, coats surfaces in industrial boilers and kettles.

Consequences of Boiler Scale

• Efficiency and Plumbing Issues:

  • Boiler scale reduces heat transfer efficiency.

  • Can lead to pipe blockages and operational inefficiencies in thermal systems.