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# Solutions - PowerPoint PPT Presentation

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

• 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

• 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.

• 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)

• 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.

• 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

• 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 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

• 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

• 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.

• The number one way of expressing concentration in chemistry

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

M = mol solute

L solution

• 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

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

• 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