Problem 36 - Chemistry The Central Science In Si Units

Question

Indicate whether each statement is true or false: (a) If you compare the solubility of a gas in water at two different temperatures, you find the gas is more soluble at the lower temperature. (b) The solubility of most ionic solids in water decreases as the temperature of the solution increases. (c) The solubility of most gases in water decreases as the temperature increases because water is breaking its hydrogen bonding to the gas molecules as the temperature is raised. (d) Some ionic solids become less soluble in water as the temperature is raised.

Step-by-Step Solution

Answer

True, False, True, True.

Step 1: Understanding Gas Solubility in Water

Gases tend to be more soluble in liquids at lower temperatures. This is because lower temperatures allow gas molecules to dissolve into the liquid rather than escape as vapor. For gas solubility in water, statement (a) is true.

Step 2: Analyzing Ionic Solid Solubility with Temperature

Most ionic solids increase in solubility as temperature rises due to the increased kinetic energy that helps break the solid into ions. Thus, statement (b) is false as it contradicts the common trend.

Step 3: Examining the Solubility of Gases and Hydrogen Bonding

As temperature increases, the solubility of gases in water generally decreases. While water molecules do have hydrogen bonds, the decrease in solubility is primarily due to increased kinetic energy, making statement (c) true because the gas molecules have more energy to enter the vapor phase.

Step 4: Considering Exceptions of Ionic Solubility Increase

Though most ionic solids become more soluble as temperature increases, there are exceptions like calcium sulfate, which become less soluble. Therefore, statement (d) is true.

Key Concepts

Gas Solubility

Gas solubility refers to the ability of gas molecules to dissolve in a solvent, such as water. A key factor affecting gas solubility is temperature. Generally, gases are more soluble in liquids at lower temperatures. This is because the kinetic energy of gas molecules decreases, allowing them to stay dissolved rather than escaping into the air. At cooler temperatures, gas molecules can fit more easily into the liquid, achieving a higher solubility. It is important to understand that when the temperature rises, the tendency for gases to become vaporized increases, leading to decreased solubility. Thus, if you have ever noticed how carbonated drinks lose their fizz faster when warm, that's due to decreased gas solubility at higher temperatures.

• Lower temperature = higher gas solubility.
• Higher temperature = lower gas solubility.

Ionic Solids

Ionic solids are made up of positively and negatively charged ions held together by strong electrostatic forces. These forces must be overcome for the solid to dissolve in a solvent like water. In most cases, as temperature increases,

• the energy provided helps to break apart these ionic bonds more easily.
• This typically results in increased solubility of ionic solids at higher temperatures.

However, it's worthwhile to note that some ionic solids, such as calcium sulfate, behave differently. They become less soluble as temperatures rise, which is a deviation from the general trend. This is an important exception to remember, demonstrating that not all ionic solubility behaviours are the same.

Temperature Effects

Temperature significantly affects the solubility of both gases and solids in liquids. For gases, higher temperatures generally increase the kinetic energy of molecules. This makes them more likely to escape the liquid phase, decreasing solubility. For ionic solids, increased temperature often leads to increased solubility because of extra energy to break the ionic bonds.
However, exceptions exist, especially for specific ionic compounds that become less soluble with increased temperature. These nuances show that while temperature effects follow general rules, understanding each specific substance's behaviour is essential. Knowing this can help predict solubility changes in different contexts, such as when mixing chemicals in a lab setting or even just dissolving a spoonful of sugar in your coffee.

Hydrogen Bonding

Hydrogen bonding is a type of dipole-dipole attraction between molecules that occurs when a hydrogen atom covalently bound to a highly electronegative element, such as oxygen, interacts with another electronegative atom. In the context of solubility,

• hydrogen bonds play a crucial role, particularly in the solubility of gases in water.
• These bonds help water molecules "hold on" to gas molecules, aiding in their solubility.

However, as temperature increases, water’s hydrogen bonds are more frequently broken due to higher kinetic energy, reducing the interactions between the gas and water molecules and thus decreasing solubility. While hydrogen bonding is a unique and specific interaction, it does not solely dictate solubility behaviors across all substances, but its impact is significant when considering the characteristics of water as a solvent.