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Water and Solutions

Water and Solutions. Physical Science Chapter 9.1. Examples of Solutions. A solution is homogeneous at a molecular level Everything is evenly dispersed in the liquid An alloy is a solution of two or more metals Steel is an alloy of iron and carbon. Solvents and Solutes.

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Water and Solutions

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  1. Water and Solutions Physical Science Chapter 9.1

  2. Examples of Solutions • A solution is homogeneous at a molecular level • Everything is evenly dispersed in the liquid • An alloy is a solution of two or more metals • Steel is an alloy of iron and carbon

  3. Solvents and Solutes • Solvents is the part of the mixture that has the greatest amount (the milk in chocolate milk) • Solute is the other part (the chocolate in chocolate milk) • When the solute is distributed evenly in the solvent we say it is dissolved.

  4. Molecular Level Analysis • Solids dissolve when molecules of solvent interact with and separate molecules of the solute. • Heat speeds this up • Crushing or grinding speeds this up • Stirring speeds this up

  5. Solubility • Solubility means the amount of solute that can be dissolved in a solvent. • Because temperature affects solubility, this is always given with a temperature. • 37.7 grams NaCl per 100 mL H2O at 25ºC • KNO3 Potassium Nitrate • KCl Potassium Chloride • Na2SO4 Sodium Sulfate

  6. Insoluble • Not everything dissolves • Not everything dissolves in every liquid • Chalk dust and water is not a solution

  7. Saturation • A solvent, at a given temperature, will only hold a certain amount of solute. The point at which it will hold no more solute is the saturation point.

  8. Concentration • The exact amount of solute dissolved in a given amount of solvent • 10.0 g sugar in 90.0 g water • This is a 10% solution

  9. Low Concentrations • Parts per million (ppm) • Parts per billion (ppb) • A pinch of salt in 10 tons of potato chips • Parts per trillion (ppt)

  10. Equilibrium • Things go into solution • While things are going out of solution • At equilibrium, things are dissolving at the same rate they are coming out of solution-- the solution is saturated • If we heat something, add a solute, then cool it down the solution becomes supersaturated. • These are unstable!!

  11. Solubility of Gases • Fizz in soft drinks is CO2 dissolved in water. • Solubility of gases increases with pressure. • Fish breathe oxygen dissolved in water. • Solubility of gases decreases with temperature.

  12. Water as a Solvent • Universal solvent • Polar molecule • One side attracts + ions, one side attracts - ions • Separate groups of molecules into individual molecules • Does not dissolve oil, a non-polar solvent

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