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Solutions & Concentration

Solutions & Concentration. Water. Polar molecule w/ polar bonds Causes surface tension & ability to dissolve polar molecules and ionic compounds. Solutions. a.k.a. homogeneous mixture Solutions can exist in any of the phases of matter. Gases = Air (Nitrogen and Oxygen)

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Solutions & Concentration

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  1. Solutions & Concentration

  2. Water • Polar molecule w/ polar bonds • Causes surface tension & ability to dissolve polar molecules and ionic compounds

  3. Solutions • a.k.a. homogeneous mixture • Solutions can exist in any of the phases of matter. • Gases = Air (Nitrogen and Oxygen) • Liquids = Vinegar (Water and Acetic Acid) • Solids = Steel (Iron and Carbon)

  4. What happens at the molecular level? Random motion of molecules causes mixing The solvent molecules surround the solute molecules, in a process called solvation. Go to animation

  5. Ionic compounds • Ions dissociate when they dissolve! • This is what allows them to conduct electricity when dissolved • Called electrolytes

  6. Heterogeneous Mixtures • Suspensions - mixture with large particles that settle out if left undisturbed • Colloids - mixture with medium size particles… larger than solution particles, but smaller than suspension particles

  7. Amounts of Solute • Specific amounts of solute can be dissolved at each temperature and pressure. • Unsaturated = more solute can dissolve • Saturated = maximum amount of solute dissolved • Supersaturated = more than maximum amount is dissolved • Achieved by increasing temperature, adding solute, then slowly bringing temperature back down. Sodium acetate demo!

  8. ^ unsaturated ^ supersaturated sToP & tHinK: If you have 20 grams of KNO3 in 100 g of H2O at 50 C, is it unsaturated, saturated, or supersaturated?

  9. 1) How many grams of NaNO3 can dissolve in 100 g of water at 10 C? 2) At what temperature can 80 grams of KNO3 dissolve into100 grams of water? 3) How many grams of KNO3 can dissolve into 50 g of water at 40 C?

  10. To Mix or Not To Mix… Not all substance combinations dissolve! Depends on polarity/charge…  For a solid/gas solute in a liquid solvent: If it dissolves… soluble If it doesn’t… insoluble  For a liquid solute in a liquid solvent: If it dissolves… miscible If it doesn’t… immiscible Oil / water

  11. Factors that Affect Solubility SOLID SOLUTE •  the temperature =  solubility (usually, but NOT always) •  the surface area =  solubility GAS SOLUTE •  temperature = solubility •  the pressure =  solubility (like in the gas in soda pop lab!) Alka-seltzer demo

  12. Solubility Video (5 min)

  13. Calculating Concentration • Molarity (M) • percent composition (%) • parts per million (ppm) • grams/liter (g/L)

  14. Molarity • M = moles of solute / liters of solution • Example: What is the molarity of 5 moles of iodine dissolved in water, making 50 L of solution?

  15. 2 fish / 4 Liter 2 fish / 2 Liter Molarity looks at the number of solute particles / volume of solution

  16. Percent Composition • percent by mass = (mass of solute/mass of solution) x 100 • percent by volume = (volume of solute/volume of solution) x 100 • Example: You pack a suitcase that weighs 50 kg. You add 10 kg of t-shirts. What is the percent by mass of t-shirts? • Example: You add 5 mL of acetic acid to 95 mL of water. What is the percent by volume of acetic acid?

  17. Parts per Million • Parts per million is a measure of how many parts of solute are in a million parts of solution. • ppm = (mass solute / total mass of solution) x 106 • Imagine a jar that has a million jelly beans in it. (Yummie!) If 14 of the jelly beans were yellow we could say that the yellow jelly beans had a concentration of 14 parts per million. Melamine audio ->

  18. Grams per Liter • Grams per liter represents the mass of the solute divided by the volume of the solution. • g/L = grams of solute / liters of solution • Example: You have 20 grams of sodium chloride dissolved in water with a total volume of 5 liters. What is the concentration of NaCl in grams/liter?

  19. Molar Dilutions • Making solutions of lower concentrations from higher concentrations • M1V1 = M2V2 • Example: What volume of a 3 M HCl solution is needed to make 2 L of 1 M HCl? • Example: How many liters of 6 M NaOH is required to make 2 L of 4 M NaOH?

  20. Colligative Properties • physical properties affected by the NUMBER of solute particles, NOT the solute identity • vapor pressure lowering • boiling point elevation • freezing point depression • How would dissolving 1 mole of CaCl2 differ from 1 mole of NaCl in affecting colligative properties? Club soda demo!

  21. solutions have a wider range of P & T where they are in liquid phase

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