Problem 17 - Chemistry and Chemical Reactivity

Question

You make a saturated solution of \(\mathrm{NaCl}\) at \(25^{\circ} \mathrm{C} .\) No solid is present in the beaker holding the solution. What can be done to increase the amount of dissolved \(\mathrm{NaCl}\) in this solution? (See Figure 14.12.) (a) Add more solid NaCl. (b) Raise the temperature of the solution. (c) Raise the temperature of the solution and add some NaCl. (d) Lower the temperature of the solution and add some NaCl.

Step-by-Step Solution

Answer

Raising the temperature increases NaCl solubility; choose (b) or (c).

Step 1: Understand the concept of solubility

The solubility of a substance refers to the maximum amount of the solute that can dissolve in a solvent at a given temperature. In this exercise, we're dealing with a saturated solution of NaCl at 25°C, meaning it has reached its solubility limit and cannot dissolve more NaCl unless conditions change.

Step 2: Analyze each option

Evaluate the effect of each option on the solubility of NaCl: (a) Adding more solid NaCl to a saturated solution will not increase the dissolved amount since it's already saturated. (b) Raising the temperature generally increases the solubility of solids in liquids, potentially allowing more NaCl to dissolve. (c) Both raising the temperature and adding more NaCl could lead to more NaCl dissolving since the increased temperature raises solubility limits. (d) Lowering the temperature will typically decrease solubility, so adding NaCl won't dissolve additional salt.

Step 3: Determine the best approach

The best way to increase the amount of dissolved NaCl is by increasing the temperature. As the temperature of the solution increases, more NaCl can dissolve until the solution becomes saturated at the new temperature, thus choice (b) or (c) both achieve this result.

Key Concepts

Saturated Solution

A saturated solution is a point where a solution contains the maximum amount of solute that can be dissolved in a solvent at a given temperature and pressure. In simpler terms, it is when no more solute can be dissolved. Imagine adding more sugar to already sweetened tea; eventually, no more sugar will dissolve and you will start seeing undissolved sugar at the bottom. That's when you know the solution is saturated.
It is important to note that a solution's saturation point can vary. Factors like temperature directly affect how much solute can be dissolved before reaching the saturation point.

• A saturated solution is one where the solubility limit has been reached.
• No more solute can dissolve, and any excess remains undissolved.
• Conditions such as temperature impact the solubility limit of the solution.

Understanding this concept is crucial, especially when you need to increase the amount of dissolved substance, as shown in the exercise involving NaCl at 25°C.

Temperature Effect on Solubility

Temperature plays a significant role in solubility, often acting as a controlling factor. Generally, increasing the temperature allows more solute to dissolve in a solvent. This happens because higher temperatures provide energy that helps break the interactions between solute molecules, allowing them to disperse within the solvent.
As temperature increases, the kinetic energy of molecules intensifies, making it easier for them to overcome intermolecular forces. Thus, more solute can be dissolved into the solution than at lower temperatures. However, it is worth mentioning that this rule does not apply to all solutes and solvents; there are exceptions.

• Raising the temperature can increase solubility, facilitating more solute to dissolve.
• This happens because higher temperatures boost the energy of molecules, aiding dissolution.
• Exceptions exist, so be aware that this principle doesn't universally apply to all substances.

In the case of NaCl in water, increasing the temperature will generally allow more NaCl to dissolve, which answers part of the original exercise.

NaCl Solubility

NaCl, or common table salt, is a solute that dissolves in water to a certain extent; its solubility is subject to conditions like temperature. When dealing with NaCl's solubility, one must understand that at a given temperature, water can dissolve only a certain amount of this salt.
At room temperature (approximately 25°C), NaCl reaches a point where it forms a saturated solution if too much is added. To dissolve more NaCl than its natural solubility limit in water, the temperature of the solution can be increased.
In the exercise, where a saturated NaCl solution was prepared at 25°C, the easiest way to dissolve more NaCl was to increase the temperature. This relationship between temperature and solubility is key to understanding how to manage and manipulate solutions in various scientific and practical applications.

• NaCl dissolves up to a specific solubility limit in water at a given temperature.
• Increase the temperature to surpass the saturation point and dissolve more NaCl.
• Understanding solubility allows for better control in laboratory settings and everyday tasks.

This understanding is integral to effectively manipulate saturated solutions like NaCl in dynamic scenarios.