Solutions

13.1 What is Solution?• A solution is a stable

homogeneous mixture of two or more substances uniformly dispersed throughout a single phase

• Mixtures can either be heterogeneous or homogeneous. – The particles of a

heterogeneous mixture are large enough

– In a homogeneous mixture, however, the particles are molecule-sized, so the mixture appears uniform, evenly mixed

Suspensions are temporary!

•A suspension is a mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas.

Solutions are stable homogenous mixtures

Solution is a broad term•Solvent – Dissolving

Medium (larger amount)•Solutes – dissolved particles

(smaller amount)•Water is the most common

solvent.•Water is a unique solvent

because so many substances can dissolve in it.

•Solutions in which water is the solvent are called aqueous solutions.

Solid + Solid = Solution

• Another type of solution involves one solid mixed with another solid.

• Examples include solid alloys, such as brass, bronze, and steel.

Colloids are stable heterogeneous mixture

• Heterogeneous mixtures– not the same throughout

• Suspensions– Mixture that eventually settles out

(ex. Italian dressing)

• Colloid– Mixture that does not settle out;

particles are dispersed throughout the mixture (ex. milk)

13.2 Concentration and molarity

• a measure of the amount of solute dissolved in a given quantity of solvent

• A concentrated solution has a large amount of solute

• A dilute solution has a small amount of solute

Parts Per Million (ppm)• Number of grams

of solute in 1 million gram of solvent

• One unit of concentration used in pollution measurements that involve very low concentration

• A chemical analysis shows that there are 2.2 mg of lead in exactly 500 g of water. Convert this measurement to parts per million.mass of solute: 2.2 mgmass of solvent: 500 gparts per million = ?

parts solute

1 million solvent= ppm

2.2 mg

1000 mg

1 g = 2.2 x 10-3 g

2.2 x 10-3 g

500 g

1,000,000 parts

1 million= 4.4 ppm

• Helium gas, 3.0 x 10-4 g is dissolved in 200.0g of water. Express this concentration in ppm.

mass of solute: 3.0 x 10-4 gmass of solvent: 200.0 gparts per million = ?

parts solute

1 million solvent= ppm

200 g

1,000,000 parts

1 million= 1.5ppm

3.0 x 10-4 g

% Composition by mass

% Composition = g of solute

g of solution x 100 %

What is the percentage by mass of a solution made by dissolving 0.49 g of potassium sulfate in 12.70 g of water?

0.49 K2SO4

12.70g water

=

• What is the percentage concentration of 75.0 g of ethanol dissolved in 500.0 g of water?

% Composition = g of solute

g of solution x 100 %

75.0 g ethanol

500g water

75.O g of ethanol

500g water + 75.0 g of ethanol x 100 %

=13.0 %

Molarity (M)

• Molarity (M) is a concentration unit of a solution expressed as moles of solute dissolved per liter of solution.

solution of L

solute of mol M

• What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl?

solute = 85 g KCl

solution = 400 mL

74.55 g KCl

1 mol KCl

= 1.14 mol KCl

1000 mL

1 L= 0.4 L

solution of L

solute of mol M

L 0.4

KCl mol 1.14

= 2.85 M

• An aqueous solution of sodium carbonate, Na2CO3, contains 53 g of solute in 215 mL of solution. What is it concentration (M)?

solute = 53 g Na2CO3

solution = 215 mL

105.99 g Na2CO3

1 mol Na2CO3

= 0.5 mol Na2CO3

1000 mL

1 L= 0.215 L

solution of L

solute of mol M

L 0.215

CONa mol 0.5000 32

= 2.3 M

• How many moles of sugar are dissolved in 202 mL of a 0.150 M solution? How many moles of C12H22O11 is that?

Molarity = 0.150 M

solution = 202 mL 1 L = 0.202 L1000 mL

solution of L

solute of mol M

mol = M · L = (0.150 mol/L)(0.202 L)

= 0.0303 mol C12H22O11

x

mol = M · L

• A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.50 M solution. What is the volume of the solution in liters ?

solution of L

solute of mol M

Molarity = 0.50 M

solute = 1.0 H2SO4

mol/L 0.50

mol 1.0 L

= 2.0 L H2SO4

solute = 98 g H2SO4

98.08 g H2SO4

1 mol H2SO4

= 1.0 mol H2SO4

• Determine the moles of copper that will react with 0.025 L of a 6.5 M HNO3 solution.3 Cu (s) + 8 HNO3(aq) → 3 Cu(NO3)2(aq) + 2 NO(g) + 4 H2O(l)

Molarity = 6.5 M HNO3

solution = 0.025 L

solution of L

solute of mol M

mol = M · L = (6.5 mol/L)(0.025 L)

0.1625 mol HNO3 3 mol Cu= 0.061mol Cu

8 mol HNO3

= 0.1625 mol HNO3

x

• What volume (in milliliters) of a 0.500 M solution of copper(II) sulfate, CuSO4, is needed to react with an excess of aluminum to provide 11.0 g of copper?

Molarity = 0.500 M CuSO4 solution of L

solute of mol M

Solute = 11.0 g Cu

3CuSO4(aq) + 2Al(s) → 3Cu(s) + Al2(SO4)3(aq)

L = mol / M = (0.17 mol)/(0.500 mol/L)

0.17 mol Cu 3 mol CuSO4 = 0.17 mol CuSO43 mol Cu

= 0.34 L CuSO4 = 340mL

x

solute = 11 g Cu

63.5 g Cu

1 mol Cu

= 0.17 mol Cu

Molality (m or molal)

• solute in moles and the mass of solvent in kilograms;

solvent of kg

solute of mol m

1 L = 1 Kg 1000 g = 1 Kg

1 mL = 1 g

What is the molality of a solution with 9.3 mole of NaCl in 450 g of water?

solvent of kg

solute of mol m

Mols of solute = 9.3 molKg of solvent = 450 g = 0.45 Kg

9.3 mol

0.45 Kg = 21 m

• Determine the molality of a solution of 560. g of acetone, CH3COCH3, in 620 g of water.

solution of kg

solute of mol m

Mols of solute = 560g x (1 mol/58.09 g ) = 9.6 mol

Kg of solvent = 620 g = 0.62 Kg

9.6 mol

0.62 Kg = 15.5 m

13.3 Solubility and Dissolving Process• Solubility is the ability of one substance to dissolve into

another at a given temperature and pressure• “Like dissolves Like”

– Polar compounds dissolve in other polar compounds, – nonpolar compounds dissolve in other nonpolar

compounds.– Ex: Oil (nonpolar) + Water (polar) = no solubility– Ex: Salt (ionic/Polar) + Water (Polar) = solubility– Ex: hydrocarbon(nonpolar)+ paint thinner(nonpolar)

= soluable

Miscible vs. Immiscible• liquids that are completely soluble with each

other are described as being miscible in each other.

• The two liquids that do not mix are immiscible.

• The immiscible liquids form two layers. – The polar water molecules attract each other, so

they cannot be pushed apart by the nonpolar oil molecules to form a solution.

• Water is a polar solvent, while hexane is a nonpolar solvent.

• Which of the examples above illustrates a nonpolar solute in a polar solvent?

A.NH4Cl in water

B.C10H8 in water

C.C2H5OH in hexane

D.CO(NH2) 2 in hexane

Solute Water Hexane

NH4Cl, ammonium chloride Soluble Insoluble

C10H8, naphthalene Insoluble Soluble

C2H5OH, ethanol Soluble Soluble

CO(NH2)2, urea Soluble Insoluble

Solubilities of Solid Compounds• To speed up the solubility

1. Increase the surface area, by breaking into smaller pieces– Molecules are dissolved faster when they

are apart (ex: sugar cube vs. sugar granule)

2. Agitation– Stirring or shaking– moves fresh solvent next to the solute thus

increasing the rate

3. Increase temperature– solvent molecules with greater kinetic

energy can dissolve more solute particles

Enthalpy and entropy affect solubility of salts

• The dissolving of an ionic compound involves a unique factor: the separation of ions from the lattice into individual dissolved ions.

• Dissociation is the separating of a molecule into simpler molecules, atoms, radicals, or ions.

• Dissociation can be represented as an equation.

NaCl(s) → Na+(aq) + Cl−(aq)• If water is the solvent, above dissociation

is called hydration.

Saturation of Solutions A solution that contains the

maximum amount of solute that may be dissolved under existing conditions is saturated.

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

A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

SATURATED SOLUTIONno more solute

dissolves

UNSATURATED SOLUTIONmore solute

dissolves

SUPERSATURATED SOLUTION

becomes unstable,

crystals form

concentration

Cloud seeding

• Ever heard of seeding the clouds to make them produce rain?

• Clouds- mass of air supersaturated with water vapor

• Silver Iodide (AgI) crystals are dusted into the cloud

• The AgI attracts the water, forming droplets to attract others

•What happens if 46.4 g NaCH3COO added to 100. g of 20ºC water?

It all dissolves•What happens if add 46.5 g?

Mostly dissolves•Would stirring help dissolve more?

No! It only makes what will dissolve do so faster

Solubility Equilibrium•In a saturated solution, the solute is

recrystallizing at the same rate that it is dissolving.

•When the amount of solute added to a solvent has reached its solubility limit, it is at equilibrium

•Solubility equilibrium is the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates.

Gases can dissolve in liquids• Gas solubility depends on pressure and temperature• Henry’s law states that the solubility of a gas

increases as the partial pressure of the gas on the surface of the liquid increases

• Gases are less soluble in a liquid of higher temperature because the increased molecular motion in the solution allows gas molecules to escape their loose association with the solvent molecules

• Gas is soluble at LOW temperature, HIGH pressure

SOLUBILITY, COKE

• The gas is at equilibrium with the dissolved gas in this solution.

• The equilibrium is dynamic.

• If you increase the pressure the gas molecules dissolve faster than they escape.

• The equilibrium is disturbed.

• The system reaches a new equilibrium with more gas dissolved.

• Henry’s Law. P= kC• Pressure = constant x Concentration of

gas

• Henry’s Law: Gas solubility in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid.

Solubility overview

•For gases in a liquid, as the pressure goes up-the solubility goes up

•For gases in a liquid, as the temperature goes up-the solubility goes down

•For solids in liquids, as the temperature goes up-the solubility usually goes up

13.4 Physical Properties of Solutions

• The conductivity of a substance is described as its ability to conduct an electric current.

• Electrolytes- compounds that conduct electricity when molten or dissolved– All ionic compounds (ex. NaCl)

• Nonelectrolytes- – Not composed of ionic cmpds (ex. Sucrose)

• Weak electrolytes- ex. Acetic acid• Strong electrolytes- ex. NaCl• STRONG vs. WEAK

Electrolytes

Surfactants• Surfactant

– surface active agent – interferes with H-bond,

reducing surface tension (Ex: Soaps and detergents)

– Long chain of polar and nonpolar

– Connects insoluble with water• Soap is an emulsifying agent.

– An emulsion is made of colloid-sized droplets suspended in a liquid in which they would ordinarily be insoluble, unless stabilized by an emulsifying agent, such as a soap