CHAPTER 13Solutions

Solution

Solution- A homogeneous mixture of two or more substances, the composition of which may vary.

Homogenous- Composition is uniform, cannot distinguish the two parts

Components of solutions:

Solute- The substance that is dissolved. Solvent- The substance doing the

dissolving and is normally present in excess (bigger amount). Water is the most common solvent. It is polar. Example- in sugar water, sugar is the solute

and water is the solvent

Properties of water

Water is polar- caused by the positive and negative charges of the hydrogen and oxygen

Water’s density is 1 g/mL Universal solvent- multitude of things

dissolve in water It’s the only substance that its solid form

is less dense than it’s liquid form, that’s why ice floats. Molecules are further apart in ice than in water because of air.

Types of solutions

Gaseous solutions- Two or more gases are mixed.

Example: Air (oxygen, nitrogen, and carbon dioxide)

Liquid solutions

Liquid solutions- Solutions which have a liquid solvent and either a gas, liquid or solid as the solute. (Something dissolves in a liquid.)

Aqueous solutions- water is the solvent

Solute Solvent Examplegas liquid Seltzer

liquid liquid antifreezesolid liquid salt water

Types of Solutions

Solid solutions- Solutions which have a solid solvent and either a gas, liquid, or solid solute.

Solute Solvent Examplegas solid charcoal filterliquid solid dental fillingsolid solid copper in silver

Miscible vs. Immiscible

Miscible -pair of substances can be mixed together in any proportion to form a solution.

Immiscible- pair of substances cannot be mixed together to form a solution. Example: Oil and water are immiscible.

Like dissolves like- polar dissolves polar, nonpolar dissolves nonpolar

Solubility

Solubility- Amount of solute that will dissolve in a given amount of solvent

Concentrations

Unsaturated- A solution that has less than the maximum amount of solute that can be dissolved.

Saturated- A solution that contains as much solute that can be dissolved under existing conditions of temperature and pressure. This is equilibrium.

Supersaturated- A solution that contains more than the maximum solute which can be dissolved.

Solution equilibriumEventually the water becomes so full of ions that it can no longer prevent some ions from re-attaching to the parent crystal. We call this a saturated solution and the solution is said to be in equilibrium.

Equilibrium is very dependent on temperature for most solutions.

Factors affecting solubility for solids dissolved in a liquid:

1. Temperature – as temp. increases, solubility increases

2. Surface area – increased surface area increases solubility (crush the solid)

3. Stirring – increased stirring increases solubility

4. Pressure – has no effect on solubility

Factors affecting solubility of gases dissolved in a liquid:

1. Temperature – as temp. increases, solubility decreases

2. Surface area – has no effect on solubility3. Stirring – increased stirring decreases

solubility4. Pressure – increased pressure increases

solubility (Henry’s Law)

Henry’s Law

The solubility of a gas in a liquid is also dependent on the pressure that the gas exerts on the surface of the liquid. This is Henry’s Law. Increase the pressure and solubility increases. Decrease the pressure and the solubility decreases.

Did you ever notice that you soda goes flat once it is opened?

Solubility curve diagrams

For most solids solubility in a liquid increases as temp increases.

For most gases solubility in a liquid decreases as temperature increases.

Solubility curve diagrams

Solubility curve- graphs that show what mass of solute will dissolve in 100 mL of solvent

Saturation

What is the solubility of Sodium Acetate at 60 oC?

What mass of sodium acetate will dissolve in 250 mL of water at 60 oC?

Is 40 grams of sodium acetate in 50 mL of water at 60 oC saturated, unsaturated, or supersaturated?

CH 14- SOLUTIONS

Mixtures

Mixture: blend of 2 or more kinds of matter physically, each retaining its own properties

Heterogeneous Not uniform in composition Ex) Vegetable Soup, chocolate chip cookies

Homogeneous Uniform in composition Salt Water Solutions

Alloys

Alloys are solutions of two or more metals mixing evenly (homogenous)

Ex- steel, bronze, brass, sterling silver

Suspensions

Suspension: Particles of a solvent are so large that they settle out unless they are mixed or agitated (heterogeneous)

Example: Clay in Water, Muddy Water

Colloids Colloids: Mixtures you can’t see

through Examples:

Tyndall Effect

Used to distinguish between solutions and colloids

Light is scattered when shone through a colloid

Electrolytes vs Non

Electrolyte = a substance that dissolves in water to give an electrically conducting solution. (would make a light bulb light up)Ex) Ionic solids and acids like HCl or NaCl

Nonelectrolyte = a substance that dissolves in water to give a nonconducting or very poorly conducting solution.

Ex) Covalent compounds like sugar

Dissociation

When an ionic compound dissolves in water, the ions separate from each other (cations and anions)

Ex: NaCl(s) Na+(aq) + Cl-(aq) Ex: CaCl2(s) Ca+2(aq) + 2Cl-(aq)

Properties of Solutions

StrongElectrolyte

Non-Electrolyte

- +

salt

- +

sugar

- +

acetic acid

WeakElectrolyte

Dissolution- the rate at which a substance dissolves

1. Particle size – area of solute particles exposed to the action of the solvent particles. Increase in surface area of the solute particles , solubility increases

Example: fine table salt dissolves faster than rock salt

FACTORS AFFECTING DISSOLUTION:

2.Stirring or Agitation increases the solubility of solid solute particles in a solvent. Because it hastens the contact between the surface of the solute and the solvent particles

3. Application of heat - solvent molecules move faster and come in contact frequently with the solute particles, increasing solubility.

Except for other solutes where solubility hastens with decrease in the temperature of the solvent. Example: sodium hydroxide pellets dissolves slowly in hot water than in cold water.

Solubility

Solids are more soluble at... high temperatures.

Gases are more soluble at...

• low temperatures &• high pressures

(Henry’s Law).• EX: nitrogen

narcosis, the “bends,” soda

Solubility Table

LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

shows the dependence of solubility on temperature

gases

solids

How to determine the solubility of a given substance?

Find out the mass of solute needed to make a saturated solution in 100 cm3 of water for a specific temperature(referred to as the solubility).

This is repeated for each of the temperatures from 0ºC to 100ºC. The data is then plotted on a temperature/solubility graph,and the points are connected. These connected points are called a solubility curve.

How to use a solubility graph?

A. IDENTIFYING A SUBSTANCE ( given the solubility in g/100 cm3 of water and the temperature)

• Look for the intersection of the solubility and temperature.

Example: What substance has a solubility of 90 g/100 cm3 of water at a temperature of 25ºC ?

Example:

What substance has a solubility of 200 g/100 cm3 of water at a temperature of 90ºC ?

B. Look for the temperature or solubility

•Locate the solubility curve needed and see for a given temperature, which solubility it lines up with and visa versa.

What is the solubility of potassium nitrate at 80ºC ?

At what temperature will sodium nitrate have a solubility of 95 g/100 cm3 ?

At what temperature will potassium iodide have a solubility of 230 g/100 cm3 ?

What is the solubility of sodium chloride at 25ºC in 150 cm3 of water ?

• From the solubility graph we see that sodium chlorides solubility is 36 g.

Solubility in grams = unknown solubility in grams

100 cm3 of water other volume of water

___36 grams____ = unknown solubility in grams

100 cm3 of water 150 cm3 water

 

Place this in the proportion below and solve for the unknown solubility. Solve for the unknown quantity by cross multiplying.

The unknown solubility is 54 grams. You can use this proportion to solve for the other volume of water if you're given the other solubility.

C. Determine if a solution is saturated,

unsaturated,or supersaturated.• If the solubility for a given substance places

it anywhere on it's solubility curve it is saturated.• If it lies above the solubility curve, then it's supersaturated,• If it lies below the solubility curve it's an unsaturated solution. Remember though, if the volume of water isn't 100 cm3 to use a proportion first as shown above.

Temp. (oC)

Solubility(g/100 g H2O)

KNO3 (s)

KCl (s)

HCl (g)

SOLUBILITYCURVE

Solubility how much solute dissolves in a given amt.

of solvent at a given temp.

unsaturated: solution could hold more solute; below linesaturated: solution has “just right” amt. of solute; on

linesupersaturated: solution has “too much” solute dissolved in

it;above the line

To

Sol.

To

Sol.

Solids dissolved in liquids Gases dissolved in liquids

As To , solubility As To , solubility

Sometimes you'll need to determine how much additional solute needs to be added to a unsaturated solution in order to make it saturated.

For example,30 grams of potassium nitrate has been added to 100 cm3 of water at a temperature of 50ºC.

How many additional grams of solute must be added in order to make it saturated?

From the graph you can see that the solubility for potassium nitrate at 50ºC is 84 grams

If there are already 30 grams of solute in the solution, all you need to get to 84 grams is 54 more grams ( 84g-30g )

Solubility Table

LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517

shows the dependence of solubility on temperature

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

gases

solids

Classify as unsaturated, saturated, or supersaturated.

per100

gH2

O

80 g NaNO3 @ 30oC

45 g KCl @ 60oC

50 g NH3 @ 10oC

70 g NH4Cl @ 70oC

=unsaturated

=saturated

=unsaturated

=supersaturated

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

gases

solids

So sat. pt. @ 40oC for 500 g H2O = 5 x 66 g = 330 g

120 g < 330 g unsaturated

saturation point @ 40oC for 100 g H2O = 66 g KNO3

Per 500 g H2O, 120 g KNO3 @ 40oC

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

gases

solids

0 10 20 30 40 50 60 70 80 90 100

(A) Per 100 g H2O, 100 g Unsaturated; all soluteNaNO3 @ 50oC. dissolves; clear

solution.

(B) Cool solution (A) very Supersaturated; extraslowly to 10oC. solute remains in solution;

still clear.

Describe each situation below.

(C) Quench solution (A) in Saturated; extra solute an ice bath to 10oC. (20 g) can’t remain in

solution, becomes visible.

1. a. 80 g b. 42 g

2. b. 42 g KNO3 = 25g KNO3 = 60 g 100 g H2O x g H2O

3. a. 7.7 mg at 30oCb. 9.2 mg 20oC

4. 9.2 mg O2 = x mg O2

1,000 g H2O 1,000 g H2O=

=0.92 mg O2

Nosce te ipsum