SolutionsChapter 15

Coffee = solution Brass = solution

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The Triple “S” – solution, solvent, solute

• Solution: a homogeneous mixture in which the components are uniformly intermingled.

• Solvent: the dissolving medium; substance present in the largest amount

• Solute: substance dissolved in a solvent

Solute + Solvent

Jayhawk says: Did you know solutions with water as the solvent areAqueous solutions?

The Triple “S” – solution, solvent, solute

• When a solid is being dissolved in a liquid to form a solution, three factors affect the speed of the dissolving process; Surface area, stirring and temperature.

Solute + Solvent

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Solubility

• Solids

• Gases

The most commonly used expression of concentration is molarity.

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M = moles of solute liter of solution

Examples:

#1) A solution contains 0.90 mol of NaCl in 0.50 L of water. Calculate the M of this solution.

0.90 mol NaCl = 1.8 M 0.50 L H2O

Jayhawk says:Remember to convert to liters if given milliliters.

#2) A solution contains 1.2 g of Magnesium chloride in 100 mL ofWater. Calculate the M.

Answer:

1.2g MgCl2 x 1 mol MgCl2 = 0.013mol MgCl2 93.2 g MgCl2

Jayhawk says:Remember significant figure rules.

0.013 mol MgCl2 = 0.13 M0.100 L H2O

Another Example!!

A 0.40 M solution of glucose contains 8 moles of the solute. What is the volume of this solution?

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Answer:

Molarity = mol solute L of soln

Jayhawk says:Remember significant figure rules.

So, L (volume) of soln = mol solute Molarity

L = 8 mol 0.40 M

Volume = 20 L

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Molality is the number of moles of a given substance per kilogram of solvent.

• m = Moles of soluteKg of Solvent

•"one molal solution", i.e. a solution which contains one

mole of the solute per 1000 grams of the solvent.

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A solution is prepared by dissolving 0.500 mol of NaCl in 1.000 Kg of H20. Calculate the molality.

A solution contains 1.5 mol of NaCl in 100. g of H20. Calculate the molality.

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How many g of potassium iodide must be dissolved in 500. g of water to give a 0.060 molal solution?

Mole Fraction

• Ratio of the number of moles of solute to number of moles of solute and solvent (solution)

•To concentrate a solution, one must add more solute, or reduce the amount of solvent (for instance, by selective evaporation). •By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute.

•The # of moles of solute stays constant. More H20 is added which increases the volume while decreasing the Molarity.

Light, and able to see through, (lightly concentrated)

Dilution Equation:

M(1)V(1) = M(2)V(2)

•M(1)V(1) are the initial conditions

•M(2)V(2) are the final conditions (dilute)

How would you prepare 100 mL of 0.40 M MgSO4 from a stock solution of 2.0 M MgSO4?

You have 1000 mL of 1.0 M HCl in your stockroom. You need 15 mL of 0.02 M solution for a lab. How much of the original solution will you need to make this solution?

Dilution Equation:

M(1)V(1) = M(2)V(2)

•M(1)V(1) are the initial conditions

•M(2)V(2) are the final conditions (dilute)

Saturated SolutionUnsaturated SolutionSupersaturated Solution

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- volume of solute x 100 volume of soln - used for liquids dissolved within liquids

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Calculate the % V of isoprpopanol when 20. mL of the alcoholIs diluted with water for a final volume of 100. mL

A soln has a total V of 1000 mL after water was added to 25 mL of ethanol. What is the % V of the ethanol soln?

• mass of solute x 100 mass of soln • grams of solution = grams of solute + grams of solvent

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A hydrochloric acid soln was made by adding 59.26 g of HCl to 100 g H20. Calculate the % mass of HCl in the soln.

Calculate the mass % of octane when 10.5 g C8H18

is mixed with 40.0 g of C6H14. Octane is the solute.

• mass of solute x 100 volume of soln • most often seen with g/mL units, but g/L are o.k. (make sure to label)

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A 100 mL soln containing 7.0 g of MgCl2 is what % mass/volume of MgCl2?

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•Calculating ion concentration from Molarity

•Solute concentration is always written in terms of the solute form before it dissolves.

•Now, we need to account for ions in soln, dissociation of ions when dissolved.

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•Needed–Solubility Tables–Balanced Equations–Net Ionic Equations – M = [ ]

Give the [ ] of all ions in the soln below

• 0.50 M Co(NO3)2

• Dissociation Rxn:

• Determine M of each ion:

Give the [ ] of all ions in the soln below

• 1.0 M FeCl3

• Dissociation Rxn:

• Determine M of each ion:

How many moles of Ag+ ions are present in 25 mL of a 0.75 M AgNO3 soln?

• Unk:

• Given:

• Dissoc. Rxn:

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• Incorporating Stoichiometry, road maps, with new soln. info.

• Use M, molarity: mol , L as a conversion factor between moles and Liters

L mol

• Never use 22.4 L . This is for gases only!! mol

•Many types of problems . . .• Always start by writing a balanced equation• Make a road map• Write givens and unknown

1.0 L of 0.120 M calcium nitrate reacts with 3.0 L 0.050 M sodium chromate. What mass of the precipitate will form?

Jayhawk says: This is a limiting reactant problem. Remember those?!!

• Rxn:

•Net Ionic:

•Road Map:

•Stoich:

What volume of 2.50 M soln of silver nitrate is needed to completely precipitate out 4.2 g of silver chloride?

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• Rxn:

•Net Ionic:

•Road Map:

•Stoich:

Ammonium phosphate and calcium chloride react. 0.15 g of the ppt forms from excess (NH4)3PO4 and 416 mL of a CaCl2 soln. What must have been the [ ], in M of the CaCl2 soln?

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• Rxn:

•Net Ionic:

•Road Map:

•Stoich: