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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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solutions2
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
solutions3
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
dissolving
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.
solubility
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)
solubility6
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.
saturation
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
solution concentration units
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
weight weight percentage
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

your turn
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

weight volume percentage
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.
molarity
Molarity
  • The number one way of expressing concentration in chemistry
  • Molarity (M) = moles solute per Liter of solution

M = mol solute

L solution

molarity13
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

molarity14

= .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

molarity15
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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