Solutions Powerpoint

Understanding solutions and their properties using water as a basis for discussion.

Water (H₂O) consists of molecules with polar charges.
- The charges allow water to attract other substances, thereby making it known as the universal solvent.
Water molecules can bond to one another due to their polarity.
- This interaction is known as hydrogen bonding, which gives water many unique properties.

Ice is less dense than liquid water.
- Hydrogen bonds in ice hold the molecules in a regular structure, forming a honeycomb framework with “holes.”
- Because of its lower density, ice floats on water.

Hygroscopic: A compound that removes water from the environment (hydrates).
Desiccant: A hygroscopic substance that maintains a dry environment by removing water from the atmosphere.
- Commonly used in drying agents (e.g., in shoes, electronics).
Deliquescent: A substance that absorbs enough moisture to turn into a solution.

Solutions: Homogeneous mixtures that consist of solutes and solvents.
- Solute: The substance that is dissolved (appears to disappear or takes on the state of the solvent).
- Solvent: The substance in which the solute dissolves (does not change state).
Aqueous Solutions: Solutions where water is the solvent.
- Water is often referred to as the universal solvent.
- The solvent is usually the substance present in greater amount.

When ionic compounds dissolve in water, they dissociate into ions, which become surrounded by water molecules (hydrated).
The process of solute particles being surrounded by solvent molecules is called solvated.
Solvation processes can differ for molecular compounds (dissolving) and ionic compounds (dissociation).
Factors Affecting Solvation:
  - Agitation
  - Temperature
  - Particle Size

A substance is considered soluble if it dissolves in another substance, and insoluble if it does not.
Miscible: Substances that mix in all proportions to form a solution (e.g., water and ethanol).
Immiscible: Substances that do not form a solution in any proportion (e.g., diethyl ether and water).
Rule of thumb: “Likes dissolve likes” (referring to polarity).
Each solute has a limit to how much can dissolve in a solvent (referred to as solubility).
- Example: At 20°C, 64.2 g of NiCl₂ can dissolve in 100 g of H₂O.

The solubility of substances varies with temperature as shown in a solubility graph.
- Higher temperature generally increases the solubility of solids in liquids but increases the solubility of gases in liquids at lower temperatures.

The solubility of gases is also dependent on the pressure of the gas above the solution.
- Higher pressure results in greater solubility.
- Henry's Law: $S_1 P_1 = S_2 P_2$

Concentrated Solution: High proportion of solute to the solution.
Dilute Solution: Low proportion of solute to the solution.
Saturated Solution: Maximum amount of solute that can dissolve at a given temperature.
Unsaturated Solution: Contains less solute than the saturation limit.
Supersaturated Solution: Contains more solute than the saturation limit, can be destabilized by adding a seed crystal.

Solutions have variable composition; precise descriptions require specifying components and their amounts.
Concentration: Amount of solute in a given amount of solution.
- Molarity = moles of solute (mol) / liters of solution (L).
- Example: A 2.0 M sugar solution contains 2.0 moles of sugar per liter.

Dilution: The process of adding solvent to reduce concentration while keeping solute constant.
Dilution Formula: $M_s imes V_s = M_d imes V_d$
- Concentrations and volumes can be expressed in compatible units.

Molality: A concentration measure defined as mol of solute per kg of solvent.
Importance: Used when temperature variation is critical, avoiding volume-based concentrations like molarity.

Question Example: How to prepare a specific molarity from a stock solution.
Question Example: Determine molal concentration for given amounts of solute and solvent.

Depend only on the number of solute particles, not their identity.
- Examples include vapor pressure depression, boiling point elevation, freezing point depression.

Caused by solvent evaporation; adding a non-volatile solute decreases vapor pressure.
- More solute results in less solvent at the surface, thereby lowering evaporation rates.
Van 't Hoff Factor (i): Indicates the number of particles generated from a solute in solution.

For boiling, vapor pressure must equal atmospheric pressure. Adding solute raises the boiling point.
- Example: Salt in water increases boiling temperature, leading to faster cooking.
During freezing, solutes disturb orderly solid particle patterns, requiring additional energy removal for solidification.

Suspension: Mixtures where larger particles settle out (e.g., muddy water).
Colloid: Mixtures with intermediate particle sizes that do not settle out (e.g., milk, smoke).

The scattering of light by colloidal particles, useful for distinguishing between solutions and colloids.