Saturated And Unsaturated Solutions Pogil Answer Key

Saturated and Unsaturated Solutions: A Deep Dive with POGIL Activities

Understanding saturated and unsaturated solutions is fundamental to chemistry. This comprehensive guide delves into the concepts, explains the intricacies of solubility, and provides detailed answers and explanations for common POGIL (Process-Oriented Guided-Inquiry Learning) activities focusing on saturated and unsaturated solutions. We'll explore various aspects, including factors influencing solubility and practical applications of these concepts.

What are Saturated and Unsaturated Solutions?

A solution is a homogeneous mixture of two or more substances. The substance present in the larger amount is called the solvent, and the substance(s) dissolved in the solvent are called the solute(s). The ability of a solvent to dissolve a solute is called solubility.

• Unsaturated Solution: An unsaturated solution contains less solute than the maximum amount that can be dissolved in a given amount of solvent at a specific temperature and pressure. More solute can be added and it will completely dissolve.

• Saturated Solution: A saturated solution contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature and pressure. If you add more solute, it will not dissolve; instead, it will settle at the bottom or precipitate out of the solution.

• Supersaturated Solution: A supersaturated solution contains more solute than a saturated solution can normally hold at a given temperature and pressure. These solutions are unstable and can easily precipitate out the excess solute if disturbed.

Factors Affecting Solubility

Several factors influence the solubility of a solute in a solvent:

1. Temperature:

• Solids in Liquids: Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature. As temperature rises, the kinetic energy of the solvent molecules increases, allowing them to more effectively break apart the solute particles and pull them into solution.

• Gases in Liquids: The solubility of gaseous solutes in liquid solvents usually decreases with increasing temperature. Higher temperatures give gas molecules more kinetic energy, allowing them to escape the liquid phase more readily.

2. Pressure:

• Solids and Liquids: Pressure has a negligible effect on the solubility of solids and liquids.

• Gases: Pressure significantly affects the solubility of gases. According to Henry's Law, the solubility of a gas is directly proportional to the partial pressure of that gas above the solution. Increasing pressure increases the solubility of the gas. This is why carbonated drinks are bottled under high pressure; the increased pressure keeps more carbon dioxide dissolved in the liquid.

3. Nature of Solute and Solvent:

"Like dissolves like" is a crucial principle. Polar solvents (like water) tend to dissolve polar solutes (like sugar), while nonpolar solvents (like oil) tend to dissolve nonpolar solutes (like fats). This is because of the intermolecular forces between the solute and solvent molecules. Stronger interactions lead to higher solubility.

4. Particle Size:

Smaller solute particles dissolve faster than larger ones. This is because smaller particles have a larger surface area to volume ratio, making it easier for solvent molecules to interact with them.

POGIL Activities: Sample Problems and Solutions

POGIL activities often present scenarios requiring students to apply their understanding of saturated and unsaturated solutions. Let's examine a few examples and provide detailed solutions.

Example 1: Determining Saturation

A student dissolves 50 grams of potassium chloride (KCl) in 100 grams of water at 20°C. The solubility of KCl in water at 20°C is 34 grams per 100 grams of water. Is the solution saturated, unsaturated, or supersaturated?

Solution:

Since the student dissolved 50 grams of KCl in 100 grams of water, and the solubility is only 34 grams per 100 grams of water, the solution is supersaturated. It contains more KCl than it can normally hold at 20°C. The excess KCl would likely precipitate out if the solution is disturbed.

Example 2: Calculating Solubility

A student prepared a saturated solution of sodium nitrate (NaNO3) by dissolving 150 grams of NaNO3 in 200 grams of water at 50°C. Calculate the solubility of NaNO3 in water at 50°C in grams per 100 grams of water.

Solution:

The solubility is the amount of NaNO3 dissolved per 100 grams of water. We can use a proportion:

150 grams NaNO3 / 200 grams water = x grams NaNO3 / 100 grams water

Solving for x:

x = (150 grams NaNO3 * 100 grams water) / 200 grams water = 75 grams NaNO3

The solubility of NaNO3 in water at 50°C is 75 grams per 100 grams of water.

Example 3: Predicting Solubility Changes

A saturated solution of sugar in water is prepared at room temperature. What will happen if the temperature is increased?

Solution:

The solubility of most solids in liquids increases with temperature. Therefore, if the temperature is increased, the solution will become unsaturated. More sugar can be dissolved in the warmer water.

Example 4: Understanding Gas Solubility

Explain why a bottle of soda fizzes when opened.

Solution:

Soda contains dissolved carbon dioxide under high pressure. When the bottle is opened, the pressure is released. The solubility of carbon dioxide decreases with decreasing pressure. This causes the dissolved carbon dioxide to come out of solution as bubbles, resulting in the fizz.

Example 5: Applications of Solubility

Give two examples of how understanding solubility is crucial in everyday life.

Solution:

1. Medicine: Many drugs are formulated as solutions or suspensions. Understanding solubility is crucial for ensuring the drug dissolves properly in the body and reaches the target site effectively.

2. Cleaning: Many cleaning products rely on the solubility of substances to remove dirt and stains. For example, detergents dissolve grease and oil, enabling their removal from clothing or surfaces.

Advanced Concepts: Solubility Product Constant (Ksp)

For sparingly soluble ionic compounds, the concept of the solubility product constant (Ksp) becomes relevant. Ksp represents the equilibrium constant for the dissolution of an ionic compound in water. A higher Ksp indicates higher solubility. Calculating Ksp and understanding its implications requires a deeper understanding of equilibrium chemistry. This is typically covered in more advanced chemistry courses.

Conclusion: Mastering Saturated and Unsaturated Solutions

Understanding saturated and unsaturated solutions is crucial for various applications in chemistry and beyond. By grasping the factors influencing solubility and practicing problem-solving through activities like POGIL exercises, you can build a strong foundation in this essential concept. Remember that continuous practice and application of these principles are key to mastering the topic. Through careful consideration of the examples and explanations provided, you should be well-equipped to tackle similar POGIL activities and demonstrate a comprehensive understanding of saturated and unsaturated solutions.