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Solutions

Solutions Solutions Solution = homogenous mixture….meaning it is the same throughout Composed of a solvent and a solute Solvent is present in largest amount Solute is present in the lesser amount Solutions Can be liquids or gases or solids Our atmosphere Nitrogen 79% = solvent

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Solutions

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  1. Solutions

  2. Solutions • Solution = homogenous mixture….meaning it is the same throughout • Composed of a solvent and a solute • Solvent is present in largest amount • Solute is present in the lesser amount

  3. Solutions • Can be liquids or gases or solids • Our atmosphere • Nitrogen 79% = solvent • Oxygen, CO2, and other gasses = solutes • Brass is a solution of zinc in copper

  4. Dissolving • Why do some things dissolve in one solvent and not another? • Oil and water will not mix, but oil will dissolve in gasoline. • General Rule of Solubility • Like-dissolves-like in regard to polarity • Water is a polar molecule and therefore will dissolve other polar solutes • Oil however is mostly nonpolar therefore it will not dissolve in water.

  5. Solubility • There is a limit to how much solute can be dissolved in a given amount of solvent • Adding too much sugar to ice tea (always some undissolved sugar) • Solubility is the maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature • Units = grams per 100 ml solvent (g/100ml)

  6. Solubility • Solubility is related to temperature • If you heat the ice tea…the sugar will dissolve • For solids in liquids…solubility tends to increase with temp. • For gasses in liquids however, the opposite is true….solubility decreases as temp. increases.

  7. Saturation • A saturated solution contains the maximum amount of dissolved solute possible given at a given temp. • Below saturation the amount of solute can vary immensely • How do you describe this? • Concentrated • Dilute

  8. Solution Concentration Units • Percent Composition • Vinegar 5% acetic acid • Hydrogen peroxide 3% hydrogen peroxide • Expressing the concentration of that particular solute in each solution • Percentage is the amount per 100 (3 common ways) • weight /weight • weight/volume • volume/volume

  9. weight/weight percentage • Weight of solute is divided by the weight of solution and then multiplied by 100 w/w% = grams solute x 100 grams solution 5.0 grams NaCl in 45.0 grams water w/w% = 5.0 grams NaCl x 100 = 10% 50.0 grams solution

  10. Your turn • How do you make 350.0 grams of a 5% (w/w) table sugar solution? • You know that 5% of the weight of the solution is sugar 350 g X 0.05 to get the weight of sugar = 17.5 g sugar The rest of the solution (350g – 17.5g = 332.5g) is water Weigh out 17.5g sugar and add it to 332.5 g water

  11. Weight / volume percentage • Instead of using grams of solution in denominator, it uses milliliters of solution w/v% = grams solute x 100 mL solution You want 100 mL of 15% (w/v) KNO3 solution. • weigh out 15 grams of KNO3 • dissolve this 15 grams into water until it reaches 100 mL in a volumetric flask.

  12. Molarity • The number one way of expressing concentration in chemistry • Molarity (M) = moles solute per Liter of solution M = mol solute L solution

  13. Molarity • How would you make a 1 M solution of KCl? 74.55g KCl diluted and dissolved to 1 L of solution in volumetric flask Do not add 74.55g KCl to 1 L of water…instead you want to end up with 1 L total solution

  14. = .958M Molarity • If 25.0 grams of KCl are dissolved into 350.0 mL solution, what is the molarity of the solution? M = moles solute/ L solution • 25.0 g KCl x 1 mol KCl = .335 mol KCl • 74.55 g KCl 350 mL x 1L = .350mL 1000mL

  15. Molarity • How would you prepare 2.00 L of a 0.550 M KCl solution? 0.550 mol KCL x 74.55g KCl x 2.00 L = 82.0g KCl L 1mol KCl 1 Take 82.0 g KCl and dissolve and dilute it to 2.00 liters

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