Chemistry: Solutions and Solubility

Vitamin Solubility

Vitamin C
- Has four hydroxyl (OH) groups.
- These OH groups make the molecule highly polar.
- Vitamin C can also engage in hydrogen bonding with water.
- Conclusion: Vitamin C is water-soluble.
- Key Reasoning Factors:
  - Water acts as a polar solvent, which solubilizes polar substances.
  - As fats consist primarily of nonpolar molecules, they are not effective at dissolving polar molecules like Vitamin C.
Vitamin K3
- Contains two carbonyl (C=O) groups that are polar; however, the geometric symmetry of the molecule leads to cancellation of the dipole moments.
- Conclusion: Vitamin K3 is fat-soluble.
- Key Reasoning Factors:
  - Again, the molecular characteristics imply that fat is largely comprised of nonpolar molecules, which can dissolve other nonpolar substances more effectively than polar ones like water.

Evaluating Solubility:
- Identify polar/ionic regions versus nonpolar regions within a molecule.
- Look for hydrogen-bond donors and acceptors within the molecular structure.
- Evaluate the symmetry of the molecule to understand cancellation of dipoles.
- Apply the principle of “like dissolves like”.
- Decide the solubility status:
- Water-soluble?
- Fat-soluble?
- Both?

Purpose:
- Provides a relationship for estimating vapor pressure at different temperatures based on the known vapor pressure at a specific temperature and the enthalpy of vaporization.
Definition:
- The equation is often not applicable when discussing normal boiling points, as at the normal boiling point, the vapor pressure is defined to be 1 atm (or 760 mmHg).

Describe the basic properties of solutions and how they form.
Predict the formation of a solution based on the molecular properties of its components.
Calculate the concentration of a solution using:
- Molarity
- Molality
- Mole Fraction
- Percent by mass
Discuss the effects of temperature and pressure on the solubility of different substances.

Air:
- Solute: Gas (oxygen, argon, etc.)
- Solvent: Gas (nitrogen)
- Description: Mixture of gases in nitrogen.
Humidity:
- Solute: Liquid (water vapor)
- Solvent: Gas (air)
- Description: Water vapor dispersed in air.
Camphor in Air:
- Solute: Solid (camphor)
- Solvent: Gas (air)
- Description: Sublimation of solid camphor into the atmosphere.
Soda Water:
- Solute: Gas (carbon dioxide)
- Solvent: Liquid (water)
- Description: CO2 gas dissolved in water under pressure.
Vinegar:
- Solute: Liquid (acetic acid)
- Solvent: Liquid (water)
- Description: Acetic acid dissolved in water.
Saltwater:
- Solute: Solid (sodium chloride)
- Solvent: Liquid (water)
- Description: NaCl crystals dissolved in water.

Definition: Moles of solute per liter of solution.
Importance:
- Describes the number of molecules of solute in one liter of solution.
Example:
- If the concentration of a sugar solution is 2.0 M, then:
  - 1 liter contains 2.0 moles of sugar.
  - 2 liters contain 4.0 moles of sugar.
  - 0.5 liters contain 1.0 mole of sugar.

Definition: Moles of solute per kilogram of solvent.
Characteristics:
- Defined based on the amount of solvent rather than the total solution.
- Does not change with temperature due to being based on mass, not volume.

Percent by Mass:
- Formula: ext{% by mass} = \frac{\text{mass of solute}}{\text{mass of solute} + \text{mass of solvent}} \times 100\%
Mole Fraction (X):
- Formula:
- X_A = \frac{\text{moles of A}}{\text{sum of moles of all components}}

Calculate the molarity of a solution made by dissolving 34.0 g of NH3 in 2000 mL of solution (MM_NH3 = 17.04 g/mol).

Check Units:
- M = mol/L
- 1 mol NH3 = 17.04 g
- 1 mL = 0.001 L
Conceptual Plan: Relationships:
- Given: 34.0 g NH3, 2000 mL solution
- Find: M, given g NH3 to mol NH3 to mL solution to L solution

Calculate the molality of a solution prepared by mixing 17.2 g of C2H6O2 with 0.500 kg of H2O (MM_C2H6O2 = 62.07 g/mol) to make 515 mL of solution.

Calculate the molality of a solution made by dissolving 34.0 g of NH3 in 2000 mL of water, given the density of water is 1.00 g/mL.

Unsaturated:
- Description: More solute can dissolve; concentration is less than the solubility limit.
Saturated:
- Description: Contains the maximum concentration possible for a given temperature and pressure.
Supersaturated:
- Description: Concentration exceeds solubility, representing a nonequilibrium state where crystals may grow.

General Observations:
- Solubility is provided in grams of solute that dissolve in 100 g of water.
- For most solid solutes, solubility increases as temperature rises when the dissolution process (\Delta H_{solution}) is endothermic.
Solubility Curves:
Used to predict the classification of a solution based on solute concentration:
- Saturated: On the line.
- Unsaturated: Below the line.
- Supersaturated: Above the line.

Graph Depiction:
- A graph displaying temperature (°C) on the X-axis against solubility (g solute in 100 g H2O) on the Y-axis.

Observation:
- The solubility of gases in water tends to decrease with increasing temperature.

Observation:
- Higher pressures generally increase the solubility of gases in liquids (such as CO2 in carbonated drinks).

Learning Objectives Summary:
- Understanding the properties of solutions, predicting outcomes based on molecular interactions, and calculating concentrations are essential for grasping the behavior of solutions in chemistry.
The effects of temperature and pressure on solubility are vital for various applications in practical scenarios such as solution preparation and gas solubility in liquids.