Chapter 13 Solutions

Cameroon: location of Lake Nyos

50 miles underneath lake Nyos CO2 is produced by molten volcanic rock (magma) and held in solution by the pressure of the water above it.

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CHAPTER OUTLINE

Type of Solutions Solubility & Saturation Soluble & Insoluble Salts Concentration Units Dilution Osmolarity Tonicity of Solutions

Tragedy in Cameroon

• Lake Nyos – lake in Cameroon, West Africa– on August 22, 1986, > 1700

people & 3000 cattle died

• Burped Carbon Dioxide Cloud Appeared From Nyos– CO2 seeps in from underground

and dissolves in lake water to levels above normal saturation

– though not toxic, CO2 is heavier than air – the people died from asphyxiation

Possible Resolution

• scientists have studied Lake Nyos and similar lakes in the region to try and keep such tragedies from reoccurring

• currently, they are trying to keep the CO2 levels in the lake water from reaching very high supersaturation levels by pumping air into the water to agitate it

By understanding solutions we are able to divert natural tragedies

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TYPE OFSOLUTIONS

A solution is a homogeneous mixture of two substances:

Solute:

Solvent:

substance being dissolved

present in smaller amount

substance doing the dissolving

present in larger amount

Solutes and solvents may be of any form of matter: solid, liquid or gas.

Common Types of Solution

Solution PhaseSolute Phase

Solvent Phase Example

gaseous solutions

gas gas air (mostly N2 & O2)

liquid solutions

gas

liquid

solid

liquid

liquid

liquid

soda (CO2 in H2O)

vodka (C2H5OH in H2O)

seawater (NaCl in H2O)

solid solutions solid solid brass (Zn in Cu)

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e.g. Brass (varies in composition)Type Color % Cu % Zn Density

g/cm3

MP

°C

Tensile

Strength

psi

Uses

Gilding reddish 95 5 8.86 1066

50K pre-83 pennies,munitions, plaques

Commercial bronze 90 10 8.80 1043

61K door knobs,grillwork

Jewelry bronze 87.5 12.5 8.78 1035

66K costume jewelry

Red golden 85 15 8.75 1027

70K electrical sockets,fasteners & eyelets

Low deep yellow

80 20 8.67 999 74K musical instruments,clock dials

Cartridge yellow 70 30 8.47 954 76K car radiator cores

Common yellow 67 33 8.42 940 70K lamp fixtures,bead chain

Muntz metal

yellow 60 40 8.39 904 70K nuts & bolts,brazing rods

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SOLUBILITY

Solutions form between solute and solvent molecules because of similarities between them.

Like dissolves Like

Ionic solids dissolve in water because the charged ions (polar) are attracted to the polar water molecules.

Non-polar molecules such as oil and grease dissolve in non-polar solvents such as kerosene.

• solutions that contain metal solutes and a metal solvent are called alloys

• when one substance (solute) dissolves in another (solvent) it is said to be soluble– salt is soluble in water,

– bromine is soluble in methylene chloride

chlorocarbon that is not miscible with water,

but will dissolve in most organic solvents

• when one substance does not dissolve in another it is said to be insoluble– oil is insoluble in water

SOLUBILITY

Salt Dissolving in Water

Solvation is the process of attraction and association of molecules of a solvent with molecules or ions of a solute. As ions dissolve in a solvent they spread out and become surrounded by solvent molecules.

partial + surround the anion partial – surround the cation

• there is usually a limit to the solubility of one substance in another– gases are always soluble in each other

– two liquids that are mutually soluble are said to be miscible

• alcohol and water are miscible• oil and water are immiscible

SOLUBILITY

Descriptions of Solubility

• saturated solutions have the maximum amount of solute that will dissolve in that solvent at that temperature

• unsaturated solutions can dissolve more solute

• supersaturated solutions are holding more solute than they should be able to at that temperature– unstable

Adding Solute to various Solutions

unsaturated

saturated

supersaturated

Supersaturated Solution

A supersaturated solution has more dissolved solute thanthe solvent can hold. When disturbed, all the solute abovethe saturation level comes out of solution.

Electrolytes• electrolytes are substances

whose aqueous solution is a conductor of electricity

• strong electrolytes, all the electrolyte molecules are dissociated into ions, SALTS

• nonelectrolytes, none of the molecules are dissociated into ions, SUGARS

• weak electrolytes, a small percentage of the molecules are dissociated into ions

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SOLUBILITY

Solubility refers to the maximum amount of solute that can be dissolved in a given amount of solvent.

Many factors affect the solubility of a solute in a solution.

Type of solute

Type of solvent

Temperature

Solubility is measured in grams of solute per 100 grams of solvent at a given temperature.

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SOLUBILITY

Solubility of most solids in water increases as temperature increases.

Using a solubility chart, the solubility of a solute at a given temperature can be determined.

For example, KNO3 has a solubility of 80 g/100 g H2O (80%) at 40 C.

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SOLUBILITYOF GASES

Solubility of gases in water decreases as temperature increases.

At higher temperatures more gas molecules have the energy to escape from solution.

Henry’s law states that the solubility of a gas is directly proportional to the pressure above the liquid.

For example, a can of soda is carbonated at high pressures in order to increase the solubility of CO2. Once the can is opened, the pressure is reduced and the excess gas escapes from the solution.

Solubility and Pressure• the solubility of gases in water depends on

the pressure of the gas

• higher pressure = higher solubility

low

er p

ress

ure

abo

ve t

he

soln

hig

her

pre

ssu

re

abo

ve t

he

soln

more gas

in solnless gas

in soln

Solubility and Pressure

When soda pop is sealed, the CO2 is under pressure. Opening the container lowers the pressure, which decreasesthe solubility of CO2 and causes bubbles to form.

Solution Concentration

• dilute solutions have low solute concentrations

• concentrated solutions have high solute concentrations

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CONCENTRATIONUNITS

The amount of solute dissolved in a certain amount of solution (occasionally amount of solvent) is called concentration.

Three types of concentration units will be studied in this class:

Mass Percent:

Molarity

Concentration =amount of solute

amount of solution

(m/m) and (m/v)

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MASS PERCENT

Mass percent (% m/m) is defined as the mass of solute divided by the mass of solution.

mass of soluteMass % (m/m) = x100

mass of solution

mass of solute + mass of solvent

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MASS/VOLUMEPERCENT

Mass/Volume percent (% m/v) is defined as the mass of solute divided by the volume of solution.

mass of soluteMass % (m/v) = x100

volume of solution

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Example 1:

What is the mass % (m/m) of a NaOH solution that is made by dissolving 30.0 g of NaOH in 120.0 g of water?

Mass of solution = 30.0 g + 120.0 g

30.0 gMass % (m/m)= x100 = 20.0 %

150.0 g

= 150.0 g

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Example 2:

What is the mass % (m/v) of a solution prepared by dissolving 5.0 g of KI to give a final volume of 250 mL?

5.0 gMass % (m/v) = x100 = 2.0 %

250 mL

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USING PERCENTCONCENTRATION

In the preparation of solutions, one often needs to calculate the amount of solute or solution.

To achieve this, percent composition can be used as a conversion factor.

Some examples of percent compositions, their meanings, and possible conversion factors are shown in the table below:

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Example 1:

A topical antibiotic solution is 1.0% (m/v) Clindamycin. How many grams of Clindamycin are in 65 mL of this solution?

65 mL solution x = 0.65 g 1.0 g Clindamycin100 mL solution

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Example 2:How many grams of solute are needed to prepare 150 mL of a 40.0% (m/v) solution of LiNO3?

150 mL solution x = 60. g LiNO3

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MOLARITY

The most common unit of concentration used in the laboratory is molarity (M).

Molarity is defined as:

Molarity =moles of solute

Liter of solution

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Example 1:

What is the molarity of a solution containing 1.4 mol of acetic acid in 250 mL of solution?

Vol. of solution =1 L

250 mL x = 0.25 L1000 mL

1.4 mol acetic acid

0.25 LMolarity = = 5.6 M

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Example 2:

What is the molarity of a solution that contains 75 g of KNO3 in 350 mL of solution?

1 mol75 g x

101.1 gMol of solute =

Vol of solvent =1 L

350 mL x = 0.35 L1000 mL

0.74 molMolarity = = 2.1 M

0.350 L

= 0.74 mol

Preparing a 1.00 M NaCl Solution

Weigh out1 mole (58.45 g)of NaCl and addit to a 1.00 Lvolumetric flask.

Step 1 Step 2

Add water todissolve theNaCl, thenadd water tothe mark.

Step 3

Swirl to Mix

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USINGMOLARITY

Molarity relationship can be used to calculate:

moles soluteMolarity =

volume of solution

Amount of solute:

Moles solute = Molarity x volume

Volume of solution:

moles soluteVolume of solution =

Molarity

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Example 1:

How many moles of nitric acid are in 325 mL of 16 M HNO3 solution?

Vol. of solution =1 L

325 mL x = 0.325 L1000 mL

mol of solute = = 5.2 mol mol

0.325 L x L161

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Example 2:

How many grams of NaHCO3 are in 325 mL of 4.50 M solution of NaHCO3?

84.0 g1.46 mol x

1 molmass of solute =

mol of solute = = 1.46 mol mol

0.325 L x L4.50

1

= 123 g

Vol. of solution =1 L

325 mL x = 0.325 L1000 mL

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Example 3:

What volume (mL) of 2.0 M NaOH solution contains 20.0 g of NaOH?

1 mol20.0 g x

40.0 gmol of solute =

Vol. In L = = 0.25 L L

0.500 mol x mol

12.0

= 0.500 mol

Vol. In mL =1000 mL

0.250 L x1 L

= 250 mL

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Example 4:

How many mL of a 0.300 M glucose (C6H12O6) IV solution is needed to deliver 10.0 g of glucose to the patient?

1 mol10.0 g x

180.1 gmol of solute =

Vol. In L = = 0.185 L L

0.0555 mol x mol

10.300

= 0.0555 mol

Vol. In mL =1000 mL

0.185 L x1 L

= 185 mL

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DILUTION

Solutions are often prepared from more concentrated ones by adding water. This process is called dilution.

When more water is added to a solution,

Frozen juice

Water Diluted juice

Volume increases

Concentration decreases

Amount of solute

remains constant

Volume and concentration are inversely proportional

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DILUTION

The amount of solute depends on the concentration and the volume of the solution.

Therefore,

M1 x V1 = M2 x V2

Concentrated solution Dilute

solution

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Example 1:

What is the molarity of the final solution when 75 mL of 6.0 M KCl solution is diluted to 150 mL?

M2 = 3.0 M

1 12

2

M VM =

V

M1 = 6.0 M

V1 = 75 mL

M2 = ???

V2 = 150 mL

M1 x V1 = M2 x V2

(6.0 M)(75 mL)=

150 mL

Volume increases

Concentration decreases

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Example 2:

What volume (mL) of 0.20 M HCl solution can be prepared by diluting 50.0 mL of 1.0 M HCl?

V2 = 250 mL

1 12

2

M VV =

M

M1 = 1.0 M

V1 = 50.0 mL

M2 = 0.20 M

V2 = ???

M1 x V1 = M2 x V2

(1.0 M)(50.0 mL)=

0.20 M

Concentration decreases

Volume increases

Making a Solution by Dilution

M1 x V1 = M2 x V2

M1 = 12.0 M V1 = ? LM2 = 1.50 M V2 = 5.00 L

L 6250

M 12.0L 005M 1.50

V

MVM

V

VMVM

1

1

221

2211

..

dilute 0.625 L of 12.0 M solution to 5.00 L

Solution Stoichiometry

• we know that the balanced chemical equation tells us the relationship between moles of reactants and products in a reaction– 2 H2(g) + O2(g) → 2 H2O(l) implies for every 2 moles of H2

used, you need 1 mole of O2 and to make 2 moles of H2O

• molarity is the relationship between moles of solute and liters of solution, thus we can measure the moles of a material in a reaction within a solution by knowing its molarity and volume

Example 1:•How much 0.115 M KI solution, in liters, is required to completely precipitate all the Pb2+ in 0.104 L of 0.225 M Pb(NO3)2?

2 KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2 KNO3(aq)

Identify what the question is looking for:

volume of KI solution, L

0.115 M KI 0.115 mol KI 1 L solution

0.225 M Pb(NO3)2 0.225 mol Pb(NO3)2 1 L solution

Chem. Eq’n 2 mol KI 1 mol Pb(NO3)2

KI mol 0.115

nsol' KI L 1

)Pb(NO mol 1

KI mol 2

nsol' L 1

)Pb(NO mol 0.225nsol' )Pb(NO L 0.104

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2323

= 0.40696 L

= 0.407 L

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OSMOLARITY

Many important properties of solutions depend on the number of particles formed in solution.

Recall that when ionic substances (strong electrolytes) dissolve in water they form several particles for each formula unit.

For example:

NaCl (s) Na+ (aq) + Cl (aq)

1 formula unit

2 particles

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OSMOLARITY

CaCl2 (s) Ca2+ (aq) + 2 Cl (aq)

1 formula unit

3 particles

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OSMOLARITY

When covalent substances (non- or weak electrolytes) dissolve in water they form only one particle for each formula unit.

For example:

C12H22O11 (s) C12H22O11 (aq)

1 formula unit

1 particle

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OSMOLARITY

Osmolarity of a solution is its molarity multiplied by the number of particles formed in solution.

Osmolarity = i x Molarity

Number of particles in

solution

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0.10 M NaCl =

Examples:

2 particles in solution

2 x 0.10 M = 0.20 osmol

0.10 M CaCl2 =

3 particles in solution

3 x 0.10 M = 0.30 osmol

0.10 M C12H22O11 =

1 particle in solution

0.10 osmol 1 x 0.10 M =

Same molarities but different osmolarities

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TONICITY OFSOLUTIONS

Because the cell membranes in biological systems are semipermeable, particles of solute in solutions can travel in and out of the membranes. This process is called osmosis.

The direction of the flow of solutions in or out of the cell membranes is determined by the relative osmolarity of the cell and the solution.

The comparison of osmolarity of a solution with those in body fluids determines the tonicity of a solution.

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ISOTONICSOLUTIONS

Solutions with the same osmolarity as the cells (0.30) are called isotonic.

These solutions are called physiological solutions and allow red blood cells to retain their normal volume.

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HYPOTONICSOLUTIONS

Solutions with lower osmolarity than the cells are called hypotonic.

In these solutions, water flows into a red blood cell, causing it to swell and burst (hemolysis).

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HYPERTONICSOLUTIONS

Solutions with greater osmolarity than the cells are called hypertonic.

In these solutions, water leaves the red blood cells causing it to shrink (crenation).

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0.10 M NaCl =

Examples:

0.20 osmol

0.10 M CaCl2 = 0.30 osmol

0.10 M C12H22O11 = 0.10 osmol

hypotonic

isotonic

hypotonic

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THE END