3.6 Solutions and concentrations

Solutions Overview

• Definition: Homogeneous mixtures of two or more substances.

  • Components:

    • Solute: Present in lesser amount.

    • Solvent: Present in greater amount.

Types of Solutions

• Examples of Solutions: Solute and solvent can be solid, liquid, and/or gas.

Water: A Universal Solvent

• Properties:

  • Water is a polar substance that dissolves polar substances.

  • Can form hydrogen bridges, allowing it to dissolve compounds containing Oxygen, Nitrogen, and Fluorine.

• Aqueous Solutions: Solutions in which the solvent is water.

Solubility of Substances

• Definition: Measurement of how much solute can be dissolved in a certain amount of solvent at a specific temperature.

  • Types of Solutions:

    • Unsaturated: Less solute than the solubility limit.

    • Saturated: Exact amount of solute in the solvent.

    • Oversaturated: Excess of solute.

Solubility in Ionic Compounds

• Dissolution Process:

  • Ions are completely separated from the crystal solid and hydrated.

• Hydration: Water molecules surround the solute’s ions.

• Solvation: Same as hydration, but uses a different liquid.

Electrolytes

• Definition: Ionic solutes dissolved in water producing a solution that conducts electricity.

  • Types:

    • Strong Electrolyte: Completely dissociates into ions (e.g., NaCl, HCl).

    • Weak Electrolyte: Partially dissociates (e.g., HF, NH3).

    • Nonelectrolyte: Does not produce ions (e.g., sucrose).

Electrolytes in Body Fluids

• Importance: Maintain proper function of cells and organs.

  • Key Electrolytes:

    • Sodium ions: Regulate water content and carry electrical impulses.

    • Potassium ions: Involved in electrical impulses, maintain heartbeat.

    • Bicarbonate ions: Help maintain blood pH.

Solubility in Covalent Compounds

• Key Principle: "Like dissolves like"

  • Polar solutes dissolve better in polar solvents (e.g., water).

  • Non-polar solutes dissolve better in non-polar solvents (e.g., hexane).

Measuring Concentrations in Solutions

• Definition: Amount of solute dissolved in a specific amount of solution.

• Methods of Expression:

  • Mass percentage.

  • Volume percentage.

  • Mass/Volume percentage.

  • Molarity.

  • Molality.

  • Parts per million.

Mass Percentage Concentration

• Used for: Preparing solutions with solid solutes dissolved in liquids.

• Calculation:

  • ( ext{Mass ext{(mass of solute} (g))} = rac{ ext{mass of solute (g){ ext{mass of solute (g) + mass of solvent (g) imes 100\text{ ext{(percent)}} )

Calculating Mass Percentage

• Example Calculation:

  • Mixing 8.00 g of KCl with 42.00 g of water:

  • Mass percent KCl = ( rac{8.00 ext{ g KCl}}{ (8.00 ext{ g KCl}) + (42.00 ext{ g H2O})} imes 100 = 16.0 ext{ ext{(m/m)}} )

Volume Percentage

• Definition: Volume percentage measures the volume of solute in a solution.

  • ( ext{Volume (v/v)} ext{ } = rac{ ext{volume of solute}} { ext{volume of solution}} imes 100\text{(percent)} )

Mass/Volume Percentage

• Definition: Used for intravenous solutions.

• Calculation:

  • ( ext{Mass/Volume % (m/v)} = rac{ ext{grams of solute}}{ ext{milliliters of solution}} imes 100 )

Molarity

• Definition: Number of moles of solute per liter of solution.

• Calculation:

  • ( M = rac{ ext{moles of solute}}{ ext{liters of solution}})

Parts per Million (ppm)

• Used for: Very small concentrations.

• Calculation:

  • ( ext{PPM} = rac{g ext{ solute}}{g ext{ solvent}} imes 1,000,000 )