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Solutions

Solutions. Chapter 14. Solutions. Homogeneous mixture of two or more substances in a single phase Solute: substance being dissolved Solvent: dissolving medium- substance doing the dissolving; if in doubt, substance that occurs in largest amount

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Solutions

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  1. Solutions Chapter 14

  2. Solutions • Homogeneous mixture of two or more substances in a single phase • Solute: substance being dissolved • Solvent: dissolving medium- substance doing the dissolving; if in doubt, substance that occurs in largest amount • Aqueous solution (aq): solution where water is solvent

  3. Examples of Solutions

  4. Generic Terms • By soluble, we mean capable of being dissolved. • Liquids that are not soluble in each other are immiscible; liquids that are soluble in each other are miscible. • A concentrated solution has a large amount of solute as compared to solvent; a dilute solution has a small amount of solute as compared to solvent.

  5. What dissolves in what? • The general rule of thumb for deciding if two substances will dissolve in each other is “Like dissolves like.” • “Like” refers to substances with similar particle size and, more importantly, similar forces (polarity).

  6. “Like Dissolves Like” • Nonpolar solutes  nonpolar solvents • Example: SF6 dissolves in CCl4 • Polar solutes  polar solvents • Example: NH3 dissolves in H2O • But what about ionic solutes? There are no ionic solvents because ionic compounds are solids at room temp

  7. “Like Dissolves Like” (continued) • Since ionic compounds have total charges, they will dissolve in polar solvents that have partial charges • Ionic solutes  polar solvents • Example: NaCl in H2O

  8. Alcohols • Methanol (methyl alcohol) CH3OH • Ethanol (ethyl alcohol) CH3CH2OH or C2H5OH • Propanol (propyl alcohol) CH3CH2CH2OH or C3H7OH

  9. Factors Affecting the Rate of Dissolving • Surface Area • Increasing surface area of solute increases rate of dissolving • Ex: cube of sugar vs granulated sugar • Agitation • Stirring or shaking solution increases rate of dissolving • Ex: dissolving sugar without stirring vs stirring • Heat • Heating the solvent or solution increases a solid solute’s rate of dissolving into the liquid solvent • Ex: dissolving sugar in hot vs cold tea

  10. Factors Affecting Solubility • Type of solute and solvent • “Like dissolves Like” • Pressure • Only has effect on gases dissolved in liquids • Ex: colas bottle under pressure to have more fizz • Temperature • Solubility increases as temperature increases for solids dissolved in liquids • Ex: hot tea dissolves more sugar than cold tea • Solubility decreases as temperature increases for gases dissolved in liquids* • Ex: hot cola is flat (has less dissolved CO2) compared to a colder cola (has more dissolved CO2)

  11. * Henry’s Law • The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid • This is why a cola fizzes when you open it • Effervescence: the rapid escape of a gas from a liquid in which it is dissolved

  12. Amount of solute compared to amount of solvent in a solution • Unsaturated: a solution that contains less than the maximum amount of dissolved solute at a given temperature • Saturated: a solution that contains the maximum amount of dissolved solute at a given temperature • Supersaturated: a solution that contains more than the maximum amount of dissolved solute under same conditions; not stable; will crystallize with single crystal

  13. Solutions, Colloids, Suspensions

  14. Physical separation techniquesfor homogeneous mixtures • Chromatography- separates different colors of chemicals or dyes • Distillation- boil off solvent, catching the gas and re-condensing it by cooling; leaves solid solute behind • Melting Point- can separate two solids from a solution by melting (such as an alloy)

  15. Physical separation techniques for heterogeneous mixtures • Decantation- carefully pouring a solution from a container, leaving the precipitate behind • Centrifugation- involves the use of centripetal force to separate a precipitate from a solvent or separate a more dense liquid from a lighter one • Filtration- mixture is poured through a filter mesh, which allows solids to be separated from the liquid

  16. Mathematically Expressing Concentration • Molarity (M) = moles solute L solution • molality (m) = moles solute kg solvent • Mass % = grams solute x 100% grams solution

  17. Practice Problems • What is the molarity of a solution containing 22.3 g of SCl6 dissolved in CCl4 to make 4.50 L of solution? • How much water should be added to 5.00 g KCl to prepare a 0.500m solution? • How many grams of solute are in 0.750 kg of a 65.0% aqueous solution of NaBrO3?

  18. Molarity (M) = moles solute L solution solute = SCl6 solvent = CCl4 22.3 g SCl6 x 1 mol SCl6 = 0.0910 mol SCl6 (solute) 245 g SCl6 There are 4.50 L total of solution M = 0.0910 mol = 0.0202 M 4.50 L You have 0.0202 M (molar) solution of SCl6 dissolved in CCl4.

  19. molality (m) = moles solute kg solvent solute = KCl solvent = H2O 5.00 g KCl x 1 mol KCl = 0.0671 mol KCl (solute) 74.5 g KCl The solution is 0.500m KCl (aq) 0.500 m = 0.0671 mol x = 0.134 kg H2O (solvent) x You have 0.0671 mol KCl solute dissolved in 0.134 kg H2O to make a 0.500m aqueous solution.

  20. mass % = grams solute x 100% grams solution solute = NaBrO3 solvent = H2O 0.750 kg solution x 1000 g = 750. g total solution 1 kg The solution is 65.0% NaBrO3(aq) 65.0% = x x = 488 g NaBrO3 (solute) 750. g You have 488 g NaBrO3 solute dissolved in H2O solvent to make a total of 750. g of a 65.0% aqueous solution.

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