Chapter 15 - SolutionsChapter 15 - Solutions

Characteristics of solutionsCharacteristics of solutions

• Solution – homogeneous mixtureSolution – homogeneous mixture

a) parts of a solutiona) parts of a solution

i) solute – substance being dissolvedi) solute – substance being dissolved

ii) solvent – substance doing ii) solvent – substance doing dissolvingdissolving

both can be either solid, liquid, or gasboth can be either solid, liquid, or gas

Solutions do not have to be Solutions do not have to be solids in liquidssolids in liquids

gas in liquidgas in liquid

liquid in liquidliquid in liquid

solid in liquidsolid in liquid

sodasoda

vinegarvinegar

salt solutionsalt solution

exampleexamplesolutionsolution solutesolute solventsolvent

COCO22

Water/Water/syrupsyrup

saltsalt waterwater

aceticaceticacidacid waterwater

SolubilitySolubility

• Defn – ability of a solute to dissolve in a Defn – ability of a solute to dissolve in a solventsolvent

• Represented by a ___________________Represented by a ___________________

• SolubleSoluble – can be dissolved in solvent – can be dissolved in solvent

• InsolubleInsoluble – cannot be dissolved in – cannot be dissolved in solventsolvent

numerical valuenumerical value

ex: the solubility of NaCl in water is 35.9 g/100 g H2O at 20°C

““like dissolves like”like dissolves like”

•Polar (or ionic) solutes dissolve in Polar (or ionic) solutes dissolve in polar solventspolar solvents

•Nonpolar solutes dissolve in Nonpolar solutes dissolve in nonpolar solventsnonpolar solvents

““like dissolves like”like dissolves like” combocombo

Polar solute in polar solventPolar solute in polar solvent

exampleexample

sugar insugar inwaterwater

ionic solute in polar solventionic solute in polar solvent NaCl inNaCl inwaterwater

Gasoline inGasoline inoiloil

nonpolar solute in nonpolar nonpolar solute in nonpolar solventsolvent

Note that water and oil do not mix. Note that water and oil do not mix. They are insoluble.They are insoluble.

• Water does not dissolve in carbon tetrachloride Water does not dissolve in carbon tetrachloride (CCl(CCl44), but it does dissolve in milk ), but it does dissolve in milk

• Benzene (CBenzene (C66HH66) does not dissolve in water but it ) does not dissolve in water but it does dissolve in CCldoes dissolve in CCl44..

• Glucose (CGlucose (C66HH1212OO66) does not dissolve in benzene) does not dissolve in benzene but it does dissolve in milk.but it does dissolve in milk.

waterwater

CC66HH66

CClCCl44

milkmilk

glucoseglucose

polarpolar

nonpolarnonpolar

nonpolarnonpolar

polarpolar

polarpolar

Factors Affecting Rate of Factors Affecting Rate of DissolvingDissolving

• How can you dissolve something How can you dissolve something faster???faster???

a)a) increase temp of solventincrease temp of solvent

this accelerates particles creating this accelerates particles creating more particle collisionsmore particle collisions

Factors Affecting Rate of Factors Affecting Rate of SolvationSolvation

b)b) agitate the solution (stir/shake)agitate the solution (stir/shake)

more particle collisions between more particle collisions between solute and solventsolute and solvent

c)c) Increase surface area of soluteIncrease surface area of solute

breaking into smaller pieces allows breaking into smaller pieces allows more solute to be in contact w/ more solute to be in contact w/ solventsolvent

Factors that affect solubilityFactors that affect solubility

• Temperature (dissolved in liquids)Temperature (dissolved in liquids)– For solids, an increase in T, ______________For solids, an increase in T, ______________

solubility.solubility.Ex: more sugar dissolves in hot tea than in ice Ex: more sugar dissolves in hot tea than in ice

teatea

– For gases, an increase in T, ______________For gases, an increase in T, ______________solubility.solubility.

Ex: hot Coke goes flat faster than cold CokeEx: hot Coke goes flat faster than cold Coke

increasesincreases

decreasesdecreases

Factors that affect solubilityFactors that affect solubility

• PressurePressure– An increase in pressure results in an An increase in pressure results in an

______________ in solubility.______________ in solubility.

Ex: soda cans are pressurized to keep the Ex: soda cans are pressurized to keep the COCO22

dissolved. Once opened, the pressure is dissolved. Once opened, the pressure is decreases, and soda tend to get flatdecreases, and soda tend to get flat

increaseincrease

Solubility rules for ionic Solubility rules for ionic compoundscompounds

• Soluble or insoluble? (gases in liquids)Soluble or insoluble? (gases in liquids)

KCl _____________ PbSOKCl _____________ PbSO4 4 __________________________

NaNONaNO33 ___________ CaBr ___________ CaBr22 _____________ _____________

CaCOCaCO33 ___________ Fe(OH) ___________ Fe(OH)33 ___________ ___________

solublesoluble

solublesolublesolublesoluble

insolubleinsoluble insolubleinsoluble

insolubleinsoluble

Solubility TermsSolubility Terms

• how much solute can be put into how much solute can be put into solvent?solvent?

Depends on amount and temperatureDepends on amount and temperature

Unsaturated SolutionUnsaturated Solution

• Defn – less than max amt of solute Defn – less than max amt of solute dissolved at given tempdissolved at given temp

if I put sugar into water and all sugar if I put sugar into water and all sugar is dissolved, solution is unsaturatedis dissolved, solution is unsaturated

Saturated SolutionSaturated Solution

• Defn – contains max amt of solute Defn – contains max amt of solute dissolved at given tempdissolved at given temp

if I put sugar into water and not if I put sugar into water and not dissolves (you can see the sugar), dissolves (you can see the sugar), the solution is saturatedthe solution is saturated

Supersaturated SolutionSupersaturated Solution

• Defn – contains more solute dissolved Defn – contains more solute dissolved than expected at given temp than expected at given temp

(exceeds (exceeds max amount)max amount)

a saturated solution made at high a saturated solution made at high temp cools slowly. Slow cooling allows temp cools slowly. Slow cooling allows excess solute to remain dissolved in excess solute to remain dissolved in solution at lower temperaturesolution at lower temperature

very unstablevery unstable

Solubility Curve (generic)Solubility Curve (generic)

Curve Curve represenrepresents max ts max amount amount solute solute allowedallowed

Temperature

Solu

bili

ty(g

solu

te/

10

0 g

H2O

)

Unsaturated(below line)

Saturated(line and above)

10 30 50 70 90 110 130

Temperature (°C)

60

40

30

20

50

100

70

80

90

10

110

g solute/100 g H2O

What trend do you notice about the What trend do you notice about the compound above?compound above?

The higher the temp, higher the solubilityThe higher the temp, higher the solubility

What is the solubility at 70°C?What is the solubility at 70°C?

60 g/100 g H60 g/100 g H22OO

At 90°C, if 60 g is dissolved, is it saturatedAt 90°C, if 60 g is dissolved, is it saturatedor unsaturated?or unsaturated?

unsaturatedunsaturated

At 90°C, if 100 g is dissolved, is it saturatedAt 90°C, if 100 g is dissolved, is it saturatedor unsaturated?or unsaturated?

saturatedsaturated

At 40°C, how many grams of solute canAt 40°C, how many grams of solute canbe dissolved in 300 g Hbe dissolved in 300 g H22O?O?

50 x 3 = 150 g50 x 3 = 150 g

Solution Concentration Solution Concentration ProblemsProblems

• How concentrated a solution is……How concentrated a solution is……

a)a) Percent by massPercent by mass

b)b) MolarityMolarity

Percent by massPercent by mass

• Formula Formula

100 x solvent mass solute mass

solute mass

Percent By MassPercent By Mass

• Ex prob: If 3.6 g NaCl is dissolved in Ex prob: If 3.6 g NaCl is dissolved in 100 g 100 g HH22O, what is the O, what is the percent by mass?percent by mass?

3.6 g3.6 g

3.6 g + 100 g3.6 g + 100 gX 100 =X 100 = 3.5 % NaCl3.5 % NaCl

MolarityMolarity

• Formula Formula mol solute mol solute

L solutionL solution

• unitunit molmol = M = M (capital M)(capital M)

LL

Molarity Ex prob #1Molarity Ex prob #1

• A solution has a volume of 250 mL A solution has a volume of 250 mL and has 0.70 mol NaCl. What is the and has 0.70 mol NaCl. What is the molarity?molarity?

2.8 mol/Lor

2.8 M0.250 L

=0.70 mol

Molarity ex prob #2Molarity ex prob #2

• What is the molarity of a solution What is the molarity of a solution made of 47.3 g NaOH in 500 mL made of 47.3 g NaOH in 500 mL water? water?

step 1: convert grams to molesstep 1: convert grams to moles47.3 g NaOH

40 g NaOH

1 mol NaOH=1.1825 mol NaOH

Molarity ex prob #2Molarity ex prob #2

Step 2: divide moles by volume (L)Step 2: divide moles by volume (L)

2.37 mol/L NaOHor

2.37 M NaOH0.500 L

=1.1825 mol

Molarity ex prob #3Molarity ex prob #3

• How many moles of solute are How many moles of solute are present in 1.5 L of 2.4 M NaCl? present in 1.5 L of 2.4 M NaCl?

# moles = volume x molarity# moles = volume x molarity

1.5 LL

2.4 mol NaClx = 3.6 mol NaCl

DilutionsDilutions

• DiluteDilute – solution with a low solute – solution with a low solute amount amount for a given volumefor a given volume

• ConcentratedConcentrated – solution with a high – solution with a high amount of solute for a given amount of solute for a given

volumevolume

DilutionsDilutions

• How do you make a dilute solution?How do you make a dilute solution?

water down a more concentrated water down a more concentrated solutionsolution

Dilutions Dilutions

• We use the following formula to We use the following formula to determine how to make a dilutiondetermine how to make a dilution

• FormulaFormula

MM11VV11 = M = M22VV22

MM11 is more concentrated than M is more concentrated than M22

M = molarityM = molarityV = volumeV = volume

Ex #1Ex #1

• If you dilute 20 mL of a 3.5 M If you dilute 20 mL of a 3.5 M solution and make a 100 mL solution, solution and make a 100 mL solution, what is the molarity of the new what is the molarity of the new solution?solution?M1=

V1=

M2=

V2=

3.5 M ?

20 mL 100 mL

(3.5 M) (20 mL) = M2 (100 mL)

M2 = 0.7 M

Ex #2Ex #2

• You have a 6.0 M stock solution. If You have a 6.0 M stock solution. If you want to make a dilution so that you want to make a dilution so that you have 1000 mL of a 1.0 M you have 1000 mL of a 1.0 M solution, what volume of stock solution, what volume of stock solution is required?solution is required?

M1=

V1=

M2=

V2=

6.0 M 1.0 M

? 1000 mL

(6.0 M) V1 = (1.0 M)(1000 mL)

V1 = 166.7 mL

Ex #2Ex #2

• How much water is needed?How much water is needed?

Want to make 1000 mL……so must Want to make 1000 mL……so must add water to 166.7 mLadd water to 166.7 mL

1000 mL – 166.7 mL =1000 mL – 166.7 mL =833.3 mL H833.3 mL H22OO

Colligative Properties of Colligative Properties of SolutionsSolutions

• Solutes affect the physical properties Solutes affect the physical properties of their solventsof their solvents

• Colligative Properties Colligative Properties – properties – properties that depend only on the amount of that depend only on the amount of solute present, not the identitysolute present, not the identity

– includes boiling point elevation, freezing includes boiling point elevation, freezing point depressionpoint depression

Coligative Properties Coligative Properties ExamplesExamples• What happens to………What happens to………

– freezing point of water when salt is added to icy freezing point of water when salt is added to icy roads?roads?

lowers the freezing point of water, so ice lowers the freezing point of water, so ice meltsmelts

– boiling point of water when salt is added to hot boiling point of water when salt is added to hot water for making pasta?water for making pasta?

raises the boiling point of water, so it boils raises the boiling point of water, so it boils hotterhotter

General effect of solutes on General effect of solutes on solventssolvents

• Solutes __________ the freezing point Solutes __________ the freezing point of of

solvents and ___________ the boiling solvents and ___________ the boiling

point of solventspoint of solvents

lowerslowers

raisesraises