II III I Topic 7 Solutions. Solutions Homogeneous mixture of substances in the same physical state Spread uniformly throughout Particles are evenly

II

III

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Topic 7 SolutionsTopic 7 Solutions

SolutionsSolutions

Homogeneous mixture of substances in the same physical state

Spread uniformly throughoutParticles are evenly distributed

SOLUTIONSSOLUTIONS

homogeneous mixture (uniform composition throughout)

Solvent Solvent - present in greater amount

Solute Solute - substance being dissolved

Types of SolutionsTypes of Solutions

gas - both solvent/solute are gases ex. Air

liquid - gas, liquid, or solid dissolved in a liquid • ex. salt water, antifreeze

• Miscible – ex. Sugar and water• Immiscible – ex. Oil and water

Solids - 2 or more solids are uniformly spread out• alloy- ex. brass = Cu/Znbrass = Cu/Zn; steel = iron + carbonsteel = iron + carbon

aqueous –water is the solvent, (aq) ex. NaCl(aq)

SoluteSoluteSoluteSolute

A solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

SolvenSolventt

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Water in salt water Water in soda

SolvationSolvation

the process of dissolving

solute particles are separated and pulled into solution

solute particles are surrounded by solvent particles

DissociationDissociationDissociationDissociation

separation of an ionic solid into aqueous ions

NaCl(s) Na+(aq) + Cl–(aq)

Molecular SolvationMolecular SolvationMolecular SolvationMolecular Solvation

• molecules stay intact

C6H12O6(s) C6H12O6(aq)

Solvation and ConductivitySolvation and Conductivity

StrongElectrolyte

Non-Electrolyte

solute exists asions only

- +

salt

- +

sugar

solute exists asmolecules

only

- +

acetic acid

WeakElectrolyte

solute exists asions and

molecules DISSOCIATION

SolubilitySolubility

The solubility of a substance is the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution.

Solubility is often expressed in grams of solute per 100 g of solvent.

Dissolution of sodium Dissolution of sodium ChlorideChloride

Dissolution of sodium Dissolution of sodium ChlorideChloride

Hydration

““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”

depends on the forces of attraction depends on the forces of attraction Solute type nonpolar solvent polar solvent Nonpolar soluble insoluble Polar insoluble soluble Ionic insoluble soluble

Factors Affecting SolubilityFactors Affecting Solubility

• Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.

Solids –vs- GasesSolids –vs- Gases

Solids are more soluble at...Solids are more soluble at...• high temperatures.

Gases are more soluble at...Gases are more soluble at...• low temperatures &high pressures (Henry’s

Law - mass of a dissolved gas in a liquid is directly proportional to the pressure of the gas).

Rate of Solution FormationRate of Solution Formation

• The compositions of the solvent and the solute determine whether a substance will dissolve. The factors that determine how fast a substance dissolves are

• stirring (agitation)• temperature• the surface area of the dissolving particles

Solution FormationSolution Formation

• A cube of sugar in cold tea dissolves slowly.


• Granulated sugar dissolves in cold water more quickly than a sugar cube, especially with stirring.


• Granulated sugar dissolves very quickly in hot tea.


Temperature and Solution Formation • At higher temperatures, the kinetic energy of

water molecules is greater than at lower temperatures, so they move faster. As a result, the solvent molecules collide with the surface of the sugar crystals more frequently and with more force.


Stirring and Solution Formation• Stirring speeds up the dissolving process because fresh solvent (the water in tea) is continually brought into contact with the surface of the solute (sugar).


Particle Size and Solution Formation• A spoonful of granulated sugar dissolves more quickly than a sugar cube because the smaller particles in granulated sugar expose a much greater surface area to the colliding water molecules.

Therefore…Therefore…Therefore…Therefore…

Solids tend to dissolve best when:

o Heatedo Stirredo Ground into small particles

Gases tend to dissolve best when:

o The solution is coldo Pressure is high

Therefore…Therefore…Therefore…Therefore…

Solids tend to dissolve best when:• Heated • Stirred • Ground into small particles

Gases tend to dissolve best when:• The solution is cold • Pressure is high

• shows the dependence of solubility on temperature

Solubility CurvesSolubility CurvesSolubility CurvesSolubility Curves

Solubility – the ability to dissolve in water

Solubility – the ability to dissolve in water

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

concentration

• maximum grams of solute that will dissolve in 100 g of solvent at a given temperature

• varies with temp

• based on a saturated soln

SolubilitySolubilitySolubilitySolubility

SaturationSaturationSaturationSaturation

•A solution that A solution that contains the contains the maximum amount maximum amount of solute in a given of solute in a given amount of solvent.amount of solvent.

•A saturated A saturated solution is at solution is at equilibriumequilibrium•RateRatedissolvingdissolving = = RateRatecrystallizationcrystallization


• In a saturated solution, the rate of dissolving equals the rate of crystallization, so the total amount of dissolved solute remains constant.

• NaCl(s) NaCl(aq)


• A saturated solution contains the maximum amount of solute for a given quantity of solvent at a given temperature and pressure.

• An unsaturated solution contains less solute than a saturated solution at a given temperature and pressure.

UnsaturatedUnsaturatedUnsaturatedUnsaturated

A solution that A solution that contains less contains less solute than a solute than a saturated saturated solution under solution under existing existing conditions is conditions is unsaturatedunsaturated..

SupersaturatedSupersaturatedSupersaturatedSupersaturated

•A solution A solution that contains that contains more more dissolved dissolved solute than a solute than a saturated saturated solution under solution under the same the same conditions is conditions is supersaturatesupersaturatedd

SupersaturatedSupersaturated

• A supersaturated solution contains more solute than it can theoretically hold at a given temperature.

• The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added.


• A supersaturated solution is clear before a seed crystal is added.


• Crystals begin to form in the solution

immediately after the addition of a seed crystal.

• Excess solute crystallizes rapidly.

Practice Question #1Practice Question #1

1) According to Reference Table G, which compound solubility decreases most rapidly as the temperature changes from 10°C to 70°C?

a) NH4Cl

b) NH3 c) HCl d) KCl

Answer to problem #1Answer to problem #1

Correct Answer Number: 2Explanation: See Ref. Table G.

Notice the curves for choices 1 and 4 increase. Choice 2 and 3 both decrease but choice 2 (NH3) decreases more than 50 degrees, while HCl decreases only about 16 degrees.

MolarityMolarity

• The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent.

– A dilute solution is one that contains a small amount of solute.

– A concentrated solution contains a large amount of solute.

Concentrated vs. DiluteConcentrated vs. DiluteConcentrated vs. DiluteConcentrated vs. Dilute

Concentrations of SolutionsConcentrations of Solutions

• Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits. These contaminants include metals, pesticides, bacteria, and even the by-products of water treatment. You will learn how solution concentrations are calculated.

Quantities in SolutionsQuantities in SolutionsQuantities in SolutionsQuantities in Solutions

The amount of solute in a solution.

Describing Concentration

• % by mass - medicated creams

• % by volume - rubbing alcohol

• ppm, ppb - water contaminants

• molarity - used by chemists

• molality - used by chemists

MolarityMolarity

• Molarity (M) is the number of moles of solute dissolved in one liter of solution.

• To calculate the molarity of a solution, divide the moles of solute by the volume of the solution.

MolarityMolarity

• To make a 0.25 molar (0.25M) solution, first add ? mol of solute to a 0.50-L (500mL) volumetric flask half filled with distilled water.

Solve for MolesSolve for Moles

Solute used is NaClWe want to prepare 500 mL of a 0.25

Molar solutionUsing the Molarity formula solve for

moles of solute

M = Moles of Solute

Liters of Soln

Plug in NumbersPlug in Numbers

0.250 mol/Liter = x moles

0.500L

# of Moles = 0.250mol/liter x 0.500 L

x = 0.125 moles

Convert Moles to GramsConvert Moles to Grams

0.125 moles NaCl ? GramsUse Mole Conversion Formula

Moles = given mass

gfm

Plug in NumbersPlug in Numbers

0.125 moles = x grams

58 g/mol (gfm of NaCl)

X= 7.25 grams NaCl

MolarityMolarity

• Add 7.25 grams of NaCl to water in flask• Swirl the flask carefully to dissolve the solute.

MolarityMolarity

• Fill the flask with water exactly to the 500-mL mark.

16.2

#1: How many moles of NaOH are contained in 200 ml of 0.1M solution of NaOH?

2) Which solution is the most concentrated?

a) 1 mole of solute dissolved in 1 liter of solution? b) 2 moles of solute dissolved in 3 liters of solution? c) 6 moles of solute dissolved in 4 liters of solution?

d) 4 moles of solute dissolved in 8 liters of solution?

Answer: moles = (M)(L) = (0.1 M)(.2L) =.02 mol

Correct Answer Number: 3 Explanation: #3 (1.5 M. ) is the most concentrated. Find the molarity ( moles of solute/liter of solution) for

each answer.

#1) 1 mole / 1 liter or 1 M. #2) 2 moles / 3 liters or 0.67 M. #3) 6 moles / 4 liters or 1.5 M. #4) 4 moles / 8 liters or 0.5 M.

Answer:M = (moles)/(L) = 1.50 moles .5000L = 3.00 M

Ex #2: What is the molarity of a 500.0 mL solution of NaOH (GFM = 40.0g) with 60.0 g of NaOH (aq)?

Different style problemDifferent style problem

1) Which solution is the most concentrated?

a) 1 mole of solute dissolved in 1 liter of solution? b) 2 moles of solute dissolved in 3 liters of solution? c) 6 moles of solute dissolved in 4 liters of solution? d) 4 moles of solute dissolved in 8 liters of solution?

Answer to different style problemAnswer to different style problem

Correct Answer Number: 3 Explanation: #3 (1.5 M. ) is the most

concentrated. Find the molarity ( moles of solute/liter of solution) for

each answer.

#1) 1 mole / 1 liter or 1 M. #2) 2 moles / 3 liters or 0.67 M. #3) 6 moles / 4 liters or 1.5 M. #4) 4 moles / 8 liters or 0.5 M.

Percent SolutionsPercent Solutions

• Concentration in Percent (Volume/Volume)

16.2


• Isopropyl alcohol (2-propanol) is sold as a 91% solution. This solution consist of 91 mL of isopropyl alcohol mixed with enough water to make 100 mL of solution.

16.2




• Concentration in Percent (Mass/Mass)

16.2

A 50.0 gram sample of a solution is evaporated and found to contain 0.100 grams of sodium chloride. What is the percent by mass of sodium chloride in the solution?

% mass = 0.100 g X 100 50.0 g

= 0.200%

100.0 grams of water is evaporated and analyzed for lead. 0.00010 grams of lead ions are found. What is the concentration of the lead, in parts per million?

ppm = grams of solute x 1,000,000 grams of solution

= (0.00010 g) x 1,000,000 100.00010 g = .9 ppm

•If the legal limit for lead in the water is 3.0 ppm, then the water sample is within the legal limits (it’s safe and ok)

Colligative Properties of Solutions

Colligative Properties of Solutions

The wood frog is a remarkable creature because it can survive being frozen. Scientists believe that a substance in the cells of this frog acts as a natural antifreeze, which prevents the cells from freezing. You will discover how a solute can change the freezing point of a solution.

16.3

Colligative PropertiesColligative Properties

depend on the number of particles (molality) rather than the nature of the particles in the solution.

Boiling point, freezing point, vapor pressure and osmotic pressure are some of the properties affected.

Vapor-Pressure LoweringVapor-Pressure Lowering

• In a solution, solute particles reduce the number of free solvent particles able to escape the liquid. Equilibrium is established at a lower vapor pressure.

16.3

Freezing Point Depression Freezing Point Depression

• f.p. of a solution is lower than f.p. of the pure solvent

Boiling Point ElevationBoiling Point Elevation

Solute particles weaken IMF in the solvent.

b.p. of a solution is higher than b.p. of the pure solvent

ApplicationsApplications

•salting icy roads•making ice cream•antifreeze

•cars (-64°C to 136°C)•fish & insects


• Three moles of glucose dissolved in water produce 3 mol of particles because glucose

does not dissociate.

16.3

Colligative Properties Colligative Properties con’t.con’t.

Colligative Properties Colligative Properties con’t.con’t.

• # of Particles# of Particles

•Nonelectrolytes (covalent)– remain intact when dissolved –1 particle

•Electrolytes (ionic)–dissociate into ions when dissolved–2 or more particles


• Three moles of sodium chloride dissolved in water produce 6 mol of particles because each formula unit of NaCl dissociates into two ions.

16.3


• Three moles of calcium chloride dissolved in water produce 9 mol of particles because each formula unit of CaCl2 dissociates into three ions.

16.3

Boiling point elevationBoiling point elevation

called molal boiling point elevation (Kb). It is proportional to the concentration of

dissolved particles 1 mole of particles in solution raises the BP of

water by 0.52 C

Which 1 molal solution will have the highest boiling point?

KNO3 Mg(NO3)2 Al(NO3)3

Freezing Point Depression

Freezing Point Depression

called molal freezing point depression (Kf).

1 mole of particles in solution depresses the FP of water by 1.86 C

What will depress the FP of water the most….AlCl3or MgCl2? Why? What would the new FP be?

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II III I Topic 7 Solutions. Solutions Homogeneous mixture of substances in the same physical state Spread uniformly throughout Particles are evenly