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Solutions

Solutions. Solution : Homogeneous mixture, a mixture in which the components are uniformly intermingled. Solvent : Substance present in the largest amount. Solute : Substance present in the smallest amount. Aqueous Solutions : Solutions with water as the solvent. Solubility.

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Solutions

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  1. Solutions Solution: Homogeneous mixture, a mixture in which the components are uniformly intermingled. Solvent: Substance present in the largest amount. Solute: Substance present in the smallest amount. Aqueous Solutions: Solutions with water as the solvent.

  2. Solubility What happens when you dissolve NaCl in water? • When an ionic substance dissolves in water, it breaks up into individual cations and anions where are dispersed in water. There are strong water ions interactions when the solid dissolves.

  3. Solubility • Water also dissolves many nonionic substances. Sugar and ethanol dissolves in water. Both contain polar O-H groups. These H-Bond to water molecules.

  4. Solubility • Oil and water do not mix. Oil is nonpolar and water is polar. Oil floats on the surface of water because its density is less than that of water.

  5. Solution Composition:An Introduction Saturated Solution: A solution that contains as much solute as will dissolve at a given temperature. Unsaturated Solution: A solution that has not reached the limit of solute that will dissolve. Concentrated Solution: A solution that has a relatively large amount of solute dissolved. Dilute Solution: A solution that has a relatively small amount of solute dissolved.

  6. Making supersaturated solns • Make sat. soln • Cool it slowly and carefully • Lower temperatures reduced the rate of crystallization • Once disturbed (energy in), causes crystallization to occur  excess crystallized out of soln • Exothermic • Heat packs of sodium acetate (can reach 50°C!) • http://www.npr.org/programs/wesun/features/2001/dec/heatpack/011229.heatpack.html • Let’s talk about enthalpy of crystallization in lab #2

  7. Drinks carbonated under high pressure • Above 90 atmospheres • So under CO2 atmosphere • Once bottle opened, partial pressure of gas above soda plummets • CO2 solubility decreases drastically • Gas bubbles out of solution

  8. The bends • Deeper diving has higher pressures • Must use breathing tank • If it contains N2then higher pressure forces N2 to dissolve in higher amounts in blood • If ascension too fast, lower pressure causes N2 to start bubbling out of blood too quickly  rupturing of arteries  excruciatingly painful death • Must be rushed to hyperbaric chamber

  9. Antifreeze • Lowers freezing pt • Increases boiling pt • Reduces risk of radiator “boiling over” • Appreciated during the summer months in the desert • Propylene glycol replacing ethylene glycol

  10. Colloids • From Greek = “glue” • Btwn suspensions (fine sand in water, mixed up) & solns • 1) Have very high molar masses • 2) Have large sizes; starch, for ex. • 3) Tyndall effect  scatter a beam of light • 4) Do not settle out like suspensions • 5) Not the same as hemorrhoids

  11. Emulsions • Colloidal dispersions of one liquid in another • Mayo, milk • Liquids of different polarities are immiscible • Need emulsifying agent • Such as soap (one polar end, one non) & proteins (“) • In food items  soy lecithin • In the world of cleaning  surfacants (soaps, etc.)

  12. Surfacants • NaOH + animal or veggie fat  Na+ fatty acid- • The fatty acid has a long non-polar tail and a very polar carboxylate group • Can be used to take away (clean) non-polar entities like oil, dirt • Surfacants (soap) used in cleaning = detergent

  13. Detergents • Lowers surface tension of water (disrupts H-bonding) • Enhances action of detergent • Let’s watch the following video: • http://www.ilpi.com/genchem/demo/tension/#demo • Sodium lauryl sulfate (soaps, shampoos)

  14. Solution Composition:Mass Percent Mass Percent: or weight percent; describes a solution’s composition. The equation for Mass Percent is given below. Mass Percent = mass of solute x 100% mass of solution Mass Percent = grams of solute x 100% grams of solute + grams of solvent

  15. Solution Composition:Mass Percent Example A 135 g sample is evaporated to dryness, leaving 4.73 g of solid residue. Calculate the mass percent of solute present.

  16. Solution Composition: Molarity Molarity: Number of moles of solute per volume of solution in liters. Example: A solution that is 1.0 M contains 1.0 mol per 1 L of solution. The equation for Molarity is given below. M = Molarity = moles of solute =mol liters of solution L

  17. Solution Composition: Molarity Standard Solution: Solution whose concentration is accurately known. Stock Solution: Solutions that are routinely used and purchased or prepared in concentrated form. Dilution: The process of adding more solvent to a solution. Only water is added in a dilution.

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