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Solutions

Solutions. Solvation, Solubility, and Colligative Properties. Pure Substances vs. Mixtures. Pure Substances- can’t be broken down without a chemical reaction Elements and Compounds Mixtures- can be separated Heterogeneous- not the same throughout Suspensions- particles settle

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Solutions

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  1. Solutions Solvation, Solubility, and Colligative Properties

  2. Pure Substances vs. Mixtures • Pure Substances- can’t be broken down without a chemical reaction • Elements and Compounds • Mixtures- can be separated • Heterogeneous- not the same throughout • Suspensions- particles settle • Colloids- particles make “beam” (Tyndall effect) • Homogeneous- the same throughout • Solutions

  3. Solutions • Solutions made up of… • Solute- the thing that is dissolved • Solvent- the substance that the solute is dissolved in Ex: When making Kool-Aid, the powder is the SOLUTE and the water is the SOLVENT

  4. What is happening when something dissolves? • Polar Solvent & Polar (Ionic) Solute: • Polar ends attract the ions in the solid and pull them away from the crystal • They become SOLVATED – surrounded by solvent molecules • If attractions between the ions in the solute are stronger than the attractions from the solvent, it is INSOLUBLE

  5. Nonpolar Solvent & Nonpolar solute • Covalent compounds do not break up in solutions like ionic ones do • Nonpolar- no attractive OR repulsive forces • Don’t really “dissolve”, they mix because of entropy

  6. Solubility Curves • Show the amount of a solute (g) that can be dissolved in a certain amount of solvent (usually 100 g of H2O) at a certain temperature • Unsaturated solution- can dissolve more solute (under line) • Saturated solution- cannot hold any more solute at that temperature (on line) • Supersaturated- holds more solute than normal for that temperature (above line) • Must be heated and cooled quickly. One seed crystal can cause crystallization (rock candy)

  7. Practice Problem • How many grams of KNO3 should be added to 250g of water at 40°C to make a saturated solution?

  8. Colligative Properties • Colligative properties are dependent on the number of particles in a solution • Vapor Pressure Reduction/ Boiling Point Elevation • Freezing Point Depression

  9. Vapor Pressure Reduction and Boiling Point Elevation • Vapor Pressure- pressure exerted by vapor of the liquid in a closed system • If a nonvolatile solute (one that doesn’t evaporate) is added, the vapor pressure is LOWERED • Dissolved particles at the liquid surface, so less surface area for the solvent particles to escape • Results in less solvent in air • Boiling Point Elevation:Because adding a solute lowers vapor pressure, it takes more energy to vaporize the particles.

  10. Boiling Point Elevation

  11. Freezing Point Depression • Freezing Point Depression: Adding solute causes the freezing point to be LOWER • Melting requires particles to be released from a crystal • Solute molecules “get in the way” and prevent the solid molecules from being released into a liquid form

  12. Freezing Point Depression

  13. Changing Colligative Properties • Colligative properties are changed by adding solute • Change is proportional to the number of particles the solute makes • NaClwould decrease by twice as much as glucose (C6H12O6) would • glucose= covalent, NaCl= ionic • Only ionic compounds break up in solution. • MgCl2 (3 particles) would decrease it more than NaCl (2 particles)

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