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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

  • 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


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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


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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.


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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)


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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.


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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


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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


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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


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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


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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.


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Molarity

  • The number one way of expressing concentration in chemistry

  • Molarity (M) = moles solute per Liter of solution

    M = mol solute

    L solution


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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


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= .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


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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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