Chapter 12Chapter 12

Solutions and Their BehaviorSolutions and Their Behavior

SolutionsSolutions

The Solution ProcessThe Solution Process

Why do things dissolve?Why do things dissolve?

1) The driving force towards a more random state 1) The driving force towards a more random state (entropy)(entropy)

2) The attractive forces between solute and solvent 2) The attractive forces between solute and solvent (enthalpy)(enthalpy)

Intermolecular Forces!!!Intermolecular Forces!!!

SolutionsSolutions

A solution is a particular type of mixture. A solution is a particular type of mixture. Mixtures in chemistry are combinations Mixtures in chemistry are combinations of different substances where each of different substances where each substance retains its chemical properties. substance retains its chemical properties. Generally, mixtures can be separated by Generally, mixtures can be separated by non-chemical means such as filtration, non-chemical means such as filtration, heating, or centrifugation.heating, or centrifugation.

A solution is a homogeneous mixture, but A solution is a homogeneous mixture, but that's not the full definition. Homogeneous that's not the full definition. Homogeneous means that the mixture is the same all the means that the mixture is the same all the way through. You could take two same-sized way through. You could take two same-sized samples: one from the bottom and one from samples: one from the bottom and one from the top and they would be identical. the top and they would be identical. Homogeneous mixtures do not settle out if Homogeneous mixtures do not settle out if left to sit undisturbed, whereas a left to sit undisturbed, whereas a heterogeneous mixture would. Blood is a heterogeneous mixture would. Blood is a good example of a heterogeneous mixture.good example of a heterogeneous mixture.

A solution is a homogeneous mixture A solution is a homogeneous mixture where all particles exist as individual where all particles exist as individual

molecules or ions. This is the molecules or ions. This is the definition definition of a solution.of a solution.

SolutionsSolutions

A solution has two components: the solute and the A solution has two components: the solute and the solvent.solvent.

The solvent is the substance in greater amount.The solvent is the substance in greater amount. It is usually a liquid, but could be a gas or even a It is usually a liquid, but could be a gas or even a

solid. Water is defined as the universal solvent . solid. Water is defined as the universal solvent . The solute is the substance in lesser amount.The solute is the substance in lesser amount. The solute is usually a solid, but could be a liquid The solute is usually a solid, but could be a liquid

or gas. or gas.

Dissolving Process-Dissolving Process- the Solvent rips the solute apart molecule by the Solvent rips the solute apart molecule by molecule or ion by ion. If a solute is soluble that means that a molecule or ion by ion. If a solute is soluble that means that a solvent is able to rip it apart. solvent is able to rip it apart.

LIKE LIKE DISSOLVE DISSOLVE

LIKE LIKE

Polar solvents can only dissolve polar solutes and Non-Polar solvents can only dissolve non-polar solutes..

Like Dissolves LikeLike Dissolves Like

Polar dissolves Polar Non-polar dissolves Non-PolarPolar dissolves Polar Non-polar dissolves Non-Polar

Polar to PolarPolar to Polar Non-polar to Non-polarNon-polar to Non-polar

Intermolecular Forces in SolutionsIntermolecular Forces in Solutions

((ionicionic and and polarpolar substances tend to be water-soluble) substances tend to be water-soluble)

SolubilitySolubility

Solubility is the amount of a substance Solubility is the amount of a substance that will dissolve in a given amount that will dissolve in a given amount

of solventof solvent

Recall dissociation equationsRecall dissociation equations

NaClNaCl(s) (s) ⇆⇆ NaCl NaCl(aq)(aq) = Na = Na++(aq)(aq) + Cl + Cl––

(aq)(aq)

solutesolute(undissolved)(undissolved) ⇆⇆ solute solute(dissolved)(dissolved)

molecular formmolecular form ionic formionic form

Factors Affecting SolubilityFactors Affecting SolubilityMost solids are more soluble at higher temp, most gases are Most solids are more soluble at higher temp, most gases are

less soluble at higher templess soluble at higher temp

At Higher pressures there is no significant effect for solid At Higher pressures there is no significant effect for solid or liquid solutes, but there is a major effect with gaseous or liquid solutes, but there is a major effect with gaseous solutes dissolved in liquid solventssolutes dissolved in liquid solvents

Henry’s Law:Henry’s Law: gases are more soluble at higher gases are more soluble at higher pressure pressure (e.g. Pepsi/Coke/Root Beer …)(e.g. Pepsi/Coke/Root Beer …)

SSgg ∝∝ P Pgg or S or Sgg = k = kHHPPgg or S or S11/P/P11 = S = S22/P/P22

where S = solubility, P = pressure, kwhere S = solubility, P = pressure, kHH = Henry’s law constant (depends on gas) = Henry’s law constant (depends on gas)

What happens when there is to much What happens when there is to much Solute to be dissolved?Solute to be dissolved?

The Solute falls to the bottom unaffected.The Solute falls to the bottom unaffected.

What if the solute is already dissolved?What if the solute is already dissolved?

There are three types of solutions There are three types of solutions that pertain to this question.that pertain to this question.

1) Saturated 1) Saturated 2) Unsaturated 2) Unsaturated 3) Supersaturated.3) Supersaturated.

Maximum vs Minimum SolubilityMaximum vs Minimum Solubility

A solution that contains the maximum amount of dissolved A solution that contains the maximum amount of dissolved solute in a given amount of solvent is considered solute in a given amount of solvent is considered SATURATED.SATURATED.

UNSATURATED means the solution can add more solvent UNSATURATED means the solution can add more solvent at the existing conditions.at the existing conditions.

SUPERSATURATED Solution – a solution that contains SUPERSATURATED Solution – a solution that contains more than maximum solute at the given conditions a very more than maximum solute at the given conditions a very unstable solution.unstable solution.

A Supersaturated Solution VideosA Supersaturated Solution Videos

Fun with Sodium Fun with Sodium AcetateAcetate

SolubilitySolubility

SolubilitySolubility - - The concentration of solute in solution The concentration of solute in solution when the solution is saturated. (Expressed as when the solution is saturated. (Expressed as g/100 mL Hg/100 mL H22O)O)

Solubility is measured and recorded with a solubility Solubility is measured and recorded with a solubility graph.graph.

Solubility GraphSolubility GraphSolubility Curves of Pure Substances

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

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0 10 20 30 40 50 60 70 80 90 100

Temperature/Celsuis

gram

s so

lute

per

100

gra

ms

H2O

KI

NaNO3

KNO3

Ce2(SO4)3

NH3

KClO3

NH4Cl

KCl

NaCl

•The curve shows the # of grams of The curve shows the # of grams of solute in a solute in a saturated saturated solution solution containing 100 mL or 100 g of water at containing 100 mL or 100 g of water at a certain temperature.a certain temperature.

•Any amount of solute below the line Any amount of solute below the line indicates the solution is indicates the solution is unsaturatedunsaturated at at a certain temperaturea certain temperature

•Any amount of solute above the line in Any amount of solute above the line in which all of the solute has dissolved which all of the solute has dissolved shows the solution is shows the solution is supersaturatedsupersaturated..

Solution ConcentrationSolution Concentration

The word concentration refers to how much solute The word concentration refers to how much solute is dissolved.is dissolved.

Dilute means that only a little solute is dissolved Dilute means that only a little solute is dissolved and concentrated means a lot is dissolved.and concentrated means a lot is dissolved.

These are NOT numerical type numbers, but they These are NOT numerical type numbers, but they are words you should be familiar with.are words you should be familiar with.

There are three concentration words that are There are three concentration words that are numerical in nature: % by mass,numerical in nature: % by mass, molarity and molarity and molality. molality.

Percentage by massPercentage by mass

The % by mass is calculated by dividing the The % by mass is calculated by dividing the mass of solute dissolved by the mass of the mass of solute dissolved by the mass of the total solution.total solution.

100(g)solution of mass

(g) solute mass mass % x

Percentage by massPercentage by mass

Example problem:Example problem:

What is the percentage by mass of a 500.0 g What is the percentage by mass of a 500.0 g salt solution that has 25.0 g of CaClsalt solution that has 25.0 g of CaCl22 in in

475.0 g of water?475.0 g of water?

2%00.5100g 500.0

g 25.0 mass % CaClx

MolarityMolarity

The molarity of a solution is calculated by taking The molarity of a solution is calculated by taking the moles of solute and dividing by the liters of the moles of solute and dividing by the liters of solution.solution.

(L)solution liters

(mol) solute moles (M)Molarity

Molarity (M)Molarity (M)

Example #1Example #1 - Suppose we had 1.00 mole of sucrose (it's - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into some about 342.3 grams) and proceeded to mix it into some water. It would dissolve and make sugar water. We keep water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was adding water, dissolving and stirring until all the solid was gone. We then made sure that when everything was well-gone. We then made sure that when everything was well-mixed, there was exactly 1.00 liter of solution.mixed, there was exactly 1.00 liter of solution.

What would be the molarity of this solution?What would be the molarity of this solution?

The answer is 1.00 mol/L. Notice that both the units of mol The answer is 1.00 mol/L. Notice that both the units of mol and L remain. Neither cancels.and L remain. Neither cancels.

A replacement for mol/L is often used. It is a capital M. So A replacement for mol/L is often used. It is a capital M. So if you write 1.00 M for the answer, then that is correct.if you write 1.00 M for the answer, then that is correct.

MolarityMolarity

Example #2Example #2 - Suppose you had 2.00 moles of - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution. What's solute dissolved into 1.00 L of solution. What's the molarity?the molarity?

The answer is 2.00 M.The answer is 2.00 M. Notice that no mention of a specific substance is Notice that no mention of a specific substance is

mentioned at all. The molarity would be the same. mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything or any other substance. One mole of anything contains 6.02 x 10contains 6.02 x 102323 units. units.

MolarityMolarity

Now, let's change from using moles to grams. Now, let's change from using moles to grams. Example #4Example #4 - Suppose you had 100.0 grams of - Suppose you had 100.0 grams of

NaCl and you dissolved it in exactly 2.00 L of NaCl and you dissolved it in exactly 2.00 L of solution. What would be the molarity of the solution. What would be the molarity of the solution?solution?

The answer is .855 mol/L (or 0.855 M). Sometimes, The answer is .855 mol/L (or 0.855 M). Sometimes, a book will write out the word "molar," as in 0.855-a book will write out the word "molar," as in 0.855-molar.molar.

100.0 g NaCl100.0 g NaCl 1 mol NaCl1 mol NaCl 11

11 58.5 g NaCl58.5 g NaCl 2.00 L2.00 L

MolarityMolarity

Try these examples problems :Try these examples problems :

5) Calculate the molarity of 25.0 grams of KBr 5) Calculate the molarity of 25.0 grams of KBr dissolved in 750.0 mL.dissolved in 750.0 mL.

6) 80.0 grams of glucose (C6) 80.0 grams of glucose (C66HH1212OO66, mol. wt = , mol. wt =

180. g/mol) is dissolved in enough water to 180. g/mol) is dissolved in enough water to make 1.00 L of solution. What is its molarity?make 1.00 L of solution. What is its molarity?

MolalityMolality

solvent of kilograms

(mol) solute moles (m)Molality

The molality of a solution is calculated by taking the moles

of solute and dividing by the kilograms of solvent. This is a second method of calculating concentration one that becomes more useful for colligative properties.

MolalityMolality

Example #1Example #1 - Suppose we had 1.00 mole of - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to sucrose (it's about 342.3 grams) and proceeded to mix it into exactly 1.00 liter water. It would mix it into exactly 1.00 liter water. It would dissolve and make sugar water. We keep adding dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid water, dissolving and stirring until all the solid was gone. We then made sure everything was was gone. We then made sure everything was well-mixed.well-mixed.

What would be the molality of this solution? What would be the molality of this solution? Notice that my one liter of water weighs 1000 Notice that my one liter of water weighs 1000 grams (density of water = 1.00 g / mL and 1000 grams (density of water = 1.00 g / mL and 1000 mL of water in a liter). 1000 g is 1.00 kg, so:mL of water in a liter). 1000 g is 1.00 kg, so:

Molality Molality

The answer is 1.00 mol/kg. Notice that both the units The answer is 1.00 mol/kg. Notice that both the units of mol and kg remain. Neither cancels.of mol and kg remain. Neither cancels.

A replacement for mol/kg is often used. It is a lower-A replacement for mol/kg is often used. It is a lower-case m and is often in italics, case m and is often in italics, m.m. Some textbooks also Some textbooks also put in a dash, like this: 1.00-put in a dash, like this: 1.00-m.m.

MolalityMolality

Example #2Example #2 - Suppose you had 2.00 moles of solute - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solvent. What's the molality?dissolved into 1.00 L of solvent. What's the molality?

The answer is 2.00 m.The answer is 2.00 m. Notice that no mention of a specific substance is mentioned Notice that no mention of a specific substance is mentioned

at all. The molarity would be the same. It doesn't matter if it at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole is sucrose, sodium chloride or any other substance. One mole of anything contains 6.022 x 1023 units. of anything contains 6.022 x 1023 units.

MolalityMolality Now, let's change from using moles to grams. Now, let's change from using moles to grams. Example #4Example #4 - Suppose you had 100 grams of NaCl and - Suppose you had 100 grams of NaCl and

you dissolved it in exactly 2.00 kg of pure water (the you dissolved it in exactly 2.00 kg of pure water (the solvent). What would be the molality of the solution?solvent). What would be the molality of the solution?

The Answer is 0.855 mol/kg (or 0.855 The Answer is 0.855 mol/kg (or 0.855 mm). Sometimes, ). Sometimes, a book will write out the word "molal," as in 0.855-a book will write out the word "molal," as in 0.855-molal.molal.

100.0 g NaCl100.0 g NaCl 1 mol NaCl1 mol NaCl 11

11 58.5 g NaCl58.5 g NaCl 2.00 kg2.00 kg

MolalityMolality

Try these examples problems:Try these examples problems:

5) Calculate the molality of 25.0 grams of KBr 5) Calculate the molality of 25.0 grams of KBr dissolved in 750.0 mL pure water.dissolved in 750.0 mL pure water.

6) 80.0 grams of glucose (C6) 80.0 grams of glucose (C66HH1212OO66 mol. wt = mol. wt =

180. g/mol) is dissolved in1.00 kg of water. 180. g/mol) is dissolved in1.00 kg of water. Calculate the molality. Calculate the molality.

Changing the ConcentrationChanging the ConcentrationDilutionDilution

To dilute a solution means to add more To dilute a solution means to add more solventsolvent without the addition of more without the addition of more solutesolute. The . The resulting solution is thoroughly mixed and all resulting solution is thoroughly mixed and all parts of the solution are evenly distributed.parts of the solution are evenly distributed.

The total number of solute particles stays The total number of solute particles stays constant, from this you can determine the constant, from this you can determine the Concentration.Concentration.

moles before dilution = moles after dilutionmoles before dilution = moles after dilution

DilutionDilution

From the definition of molarity, we know that the From the definition of molarity, we know that the moles of solute equals the molarity times the volume.moles of solute equals the molarity times the volume.

So we can substitute MV (molarity times volume) into So we can substitute MV (molarity times volume) into the above equation, like this:the above equation, like this:

The "sub one" refers to the situation before dilution and The "sub one" refers to the situation before dilution and the "sub two" refers to after dilution.the "sub two" refers to after dilution.

MM11VV11= M= M22VV22

DilutionDilution

Example #1Example #1 - 53.4 mL of a 1.50 M solution of NaCl is on - 53.4 mL of a 1.50 M solution of NaCl is on hand, but you need some 0.800 M solution. How many mL of hand, but you need some 0.800 M solution. How many mL of 0.800 M can you make?0.800 M can you make?

Using the dilution equation, we write:Using the dilution equation, we write:

MM11VV11= M= M22VV22

(1.50 mol/L) (53.4 mL) = (0.800 mol/L) (x)(1.50 mol/L) (53.4 mL) = (0.800 mol/L) (x)

Solving the equation for x gives an answer of Solving the equation for x gives an answer of 100. mL.100. mL.

Notice that the volumes need not be converted to liters. Any Notice that the volumes need not be converted to liters. Any old volume measurement is fine, just so long as the same one old volume measurement is fine, just so long as the same one is used on each side.is used on each side.

DilutionsDilutions Example #2Example #2 - 100.0 mL of 2.500 M KBr solution - 100.0 mL of 2.500 M KBr solution

is on hand. You need 0.5500 M. What is the final is on hand. You need 0.5500 M. What is the final volume of solution which results? How do you volume of solution which results? How do you make this solution?make this solution?

MM11VV11= M= M22VV22

(2.500 mol/L) (100.0 mL) = (0.5500 mol/L) (x)(2.500 mol/L) (100.0 mL) = (0.5500 mol/L) (x)

x = x = 454.5 mL 454.5 mL Sometimes the problem might ask Sometimes the problem might ask how much more water must be added. In this last how much more water must be added. In this last case, the answer is 454.5 - 100.0 = case, the answer is 454.5 - 100.0 = 354.5 mL.354.5 mL.