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Principles of Solubility Nature of the solute and solvent

Principles of Solubility Nature of the solute and solvent. Like likes like. Electrolytes will dissolve in a polar solvent (like water) Non-electrolytes will dissolve more easily in non polar or slightly polar solvents (like benzene, or toluene).

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Principles of Solubility Nature of the solute and solvent

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  1. Principles of Solubility Nature of the solute and solvent • Like likes like. Electrolytes will dissolve in a polar solvent (like water) Non-electrolytes will dissolve more easily in non polar or slightly polar solvents (like benzene, or toluene) CH 10 Solutions

  2. Non electrolytes (molecular substances) dissolving in water. • This ‘unusual’ case will involve Hydrogen bonding or otherwise polar molecules. • Ex: • alcohols (-OH group) Methanol, Ethanol • Hydrogen peroxide H2O2 CH 10 Solutions

  3. Solubilities of Alcohols in Water Formula NameSolubility in Water (g/100 g) CH3OH methanol infinitely soluble CH3CH2OH ethanol infinitely soluble CH3(CH2)2OH propanol infinitely soluble CH3(CH2)3OH butanol 9 CH3(CH2)4OH pentanol 2.7 CH3(CH2)5OH hexanol 0.6 CH3(CH2)6OH heptanol 0.18 CH3(CH2)7OH octanol 0.054 CH3(CH2)9OH decanol insoluble in water • “greasy end” is larger proportion in large alcohols. CH 10 Solutions

  4. DDT no more mosquitoes! • Pesticide used widely in the 60’s • Soluble in non polar solvents. • Concentrates in tissues of fish, birds, and other wildlife. (biological ½ life of 8 years) • Thins eggshells. CH 10 Solutions

  5. Principles of Solubility Effect of Pressure/Henry’s Law For gases only • Solubility is directly proportional to pressure. Soda is bottled under a pressure of 4atm. This drives more of the CO2 into solution, when the cap is released, the pressure drops to 1 atm, and CO2 bubbles and rapidly escapes solution. Cg =k Pg Concentration in solution = constant x Pressure of gas CH 10 Solutions

  6. Solid + Water  Solution Usually + ΔH heat in Increased T favors an endothermic process So: Solubility of a solid usually increases with increased temperature Gas + Water  Soln. Usually –ΔH heat out Increased T is detrimental for an exothermic process So: Solubility of a gas usually decreases with higher temperature. Principles of Solubility Effect of Temperature CH 10 Solutions

  7. Molarity = moles of solute/ liters of solution Units are moles/liter Tricks: change mass to moles change mL to Liters Typical Problems Making a volume of solution from the solid. Creation Preparing a volume of a solution from another (stock) solution. Dilution Concentration Unitsproblem type 1. Molarity (M) CH 10 Solutions

  8. Prepare 35.0 mL of 0.200 M Aluminum nitrate from a solid sample. How many moles of Al-nitrate would be in the solution? Measure out that many grams and then add water to make 35.0 mL Prepare 35.0 mL of 0.20 M Aluminum Nitrate solution from a 0.50M stock solution. How many moles do you need? Remember M1V1=M2V2 McVc=MdVd Meausure out the volume of stock you need, then dilute ProblemsMolarity (M) Molar mass (gfm) of aluminum nitrate is 213.03 g/n CH 10 Solutions

  9. Problem type 2.Mole Fraction (X) • Similar to percent composition…you are interested in part of the whole • Moles of substance/ total moles • Typical problems will have you • determine the mole fraction from % mass. • determine the mole fraction of solute in solution CH 10 Solutions

  10. If you dissolve 12.0 g of methanol in 100.0 g of water. What is the mole fraction that is methanol? Determine the moles of water Determine the moles of methanol Add together for the total moles, then take part/whole ProblemsMole Fraction (X) Methane is CH4 Methanol is CH3OH CH 10 Solutions

  11. Problem type 3.Mass % Solute Solute is the solid dissolved in solution • Simply determine the percent composition by mass. • Trick is to change the decimal to a percent (x100 + “%”) CH 10 Solutions

  12. Problem Type4. Molality (m) • This is similar to molarity, but uses mass (kilograms) of the solvent, rather than liters of solvent. • Molarity (M) = # moles solute/ Liter Solvent • Typical problems will have you determine the molality from other concentration units. CH 10 Solutions

  13. What is the molality of methanol if 12g of methanol are dissolved into 100g of water? Find Moles of solute (methanol) Find kilograms of solvent Divide if the solvent is water, M and m are numerically equal 12g/32.0 g/n = 0.375 n 100g/ 1000g/kg = 0.100kg = 3.75m Problems : Molality (m) CH 10 Solutions

  14. Conversion between units- decide on a fixed amount of solution CH 10 Solutions

  15. VPL = X2Pº1 VPL= (vapor pressure lowering) X2= mole fraction of the solute Pº1= vapor pressure of the PURE solvent Each liquid has a vapor pressure. The pressure to escape the surface into the gas phase. Dissolved particles get in the way and block the escape, thereby reducing the vapor pressure. The higher the concentration (X2), the more the VP is lowered. Part III: Colligative PropertiesVapor Pressure Lowering CH 10 Solutions

  16. Raoult’s Law CH 10 Solutions

  17. ΔTb = kbm ΔTf = kfm The change in temperature from the normal boiling/freezing points is a constant (k) times the molality(m). The higher the concentration of ‘contaminant’, the greater the change in freezing/boiling points Boiling Elevation: The particles lower the vapor pressure. Kb for water is 0.52 °C/m Freezing Depression: The particles obstruct the formation of the solid crystal. There must be a lower temperature to form solid structure Kf for water is 1.86 °C/m Part III: Colligative Properties *Boiling Point Elevation ΔTb *Freezing Point Depression ΔTf CH 10 Solutions

  18. ΔTf = kfm Change in freezing temp is (Kf) x (molality) Find the freezing point of a solution containing 20.0 g of ethanol in 50.0g of water. What is the molality of the solution? Grams to moles Moles / Kg of Solvent Molality x Kf Kf for water is 1.86 °C/m Problems: Colligative Propertiesfreezing point depression CH 10 Solutions

  19. ΔTf = kbm Change in boiling temp is (Kb) x (molality) Find the boiling point of a solution containing 20.0 g of ethylene glycol in 50.0g of water. What is the molality of the solution? Grams to moles Moles / Kg of Solvent Molality x Kb Kb for water is 0.52 °C/m Problems: Colligative Propertiesboiling point elevation CH 10 Solutions

  20. π= M R T M = molarity R= .0821 L * atm/n *K T = Temperature Water moves through a semi-permeable membrane from an area of high vapor pressure to low vapor pressure. Colligative Properties Osmotic Pressure (π) CH 10 Solutions

  21. A solution is made using .0100g of a substance in 1.00g of water. The freezing point depresses 1.00 °C What is the molar mass? Solve for molarity Problems:Using freezing point depression to find molar mass CH 10 Solutions

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