Question

The solubility of \(\mathrm{Ca}(\mathrm{OH})_{2}\) is \(0.18 \mathrm{~g}\) per \(100 \mathrm{~g}\) of water at \(10^{\circ} \mathrm{C}\). Describe the solution formed when \(0.15 \mathrm{~g} \mathrm{Ca}(\mathrm{OH})_{2}\) is added to \(100.0 \mathrm{~g}\) of water.

Short answer

The solution formed by dissolving 0.15 g Ca(OH)2 in 100 g of water at 10°C is an unsaturated solution.

Step-by-step solution

Comparing the solute amount with the solubility

First compare the amount of Ca(OH)2 given in the exercise, 0.15 g, with its solubility, which is 0.18 g in 100 g of water. The amount of Ca(OH)2 added to the water is less than the solubility.

Formulate the type of the solution

Since the amount of Ca(OH)2 is less than its solubility in water, it means all the Ca(OH)2 will be dissolved in the water, producing a homogeneous solution.

Determine the saturation of the solution

Because all of the Ca(OH)2 is dissolved in the water, the solution will not be saturated. Instead, it can still dissolve up to 0.03 g of Ca(OH)2 more before becoming saturated.

Key concepts

Solubility

Solubility refers to the maximum amount of a solute that can be dissolved in a solvent at a specific temperature. In simple terms, it's how much of something can be completely mixed into a liquid before no more will dissolve.

For example, in this exercise, we are looking at \( ext{Ca(OH)}_2 \), which has a solubility of 0.18 g in 100 g of water at 10°C. This means that at 10°C, you can put up to 0.18 g of calcium hydroxide into 100 g of water, and all of it will dissolve.

Key characteristics of solubility:

• It varies with temperature, often increasing as the temperature rises.
• It is specific to each substance; different substances have different solubilities.
• Understanding solubility helps predict how substances behave when mixed together.

When the amount of the substance you add is less than the solubility, all of it will dissolve completely, as in this case with 0.15 g of \( ext{Ca(OH)}_2 \).

Saturation

Saturation occurs when a solution has reached its capacity to dissolve more solute at a particular temperature. This means the solution cannot hold any more of the solute, and additional solute will not dissolve but will remain in its solid form.

In this exercise, since only 0.15 g of \( ext{Ca(OH)}_2 \) is added to the water, it is less than its solubility limit of 0.18 g. Therefore, the solution formed is unsaturated.

An unsaturated solution simply means that more solute can still be added and will dissolve. In this case, you could add 0.03 g more of \( ext{Ca(OH)}_2 \) before reaching saturation.

Here's what to remember about saturation:

• An unsaturated solution can still dissolve more solute before reaching its solubility limit.
• A saturated solution is at its maximum concentration of solute.
• Beyond saturation, any added solute will remain undissolved.

Understanding saturation helps in determining how much of a substance can be efficiently dissolved and used in a solution.

Homogeneous Solution

A homogeneous solution is a mixture where the solute is completely dissolved in the solvent, resulting in a uniform and consistent composition throughout the solution.

This means that no matter where you sample the solution, the ratio of solute to solvent will be the same.

In the exercise presented, since 0.15 g of \( ext{Ca(OH)}_2 \) dissolves completely in 100 g of water, the solution is homogeneous.

Characteristics of a homogeneous solution include:

• The solute is evenly distributed within the solvent.
• There are no visible particles or different phases present; it looks the same everywhere.
• Common examples include saltwater or sugar dissolved in water.

In contrast, a heterogeneous mixture would have visible differences in composition, like a salad or a mixture of oil and water. Knowing the type of mixture you have can influence how you use it, especially in chemical reactions or when creating recipes.