Water and Solutions

Water and its propertiesObjectives:1. Explain surface tension2. Describe the structure of ice and liquid

water.

Water in the liquid state:Water is a polar molecule.

+ H2O

Hydrogen bonding: the negative end of the water molecule is attracted to the positive ends of other molecules- resulting in hydrogen bonding.

O

H

H

Hydrogenbond

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Water molecules “stick” together to create surface tension to support light weight objects.It also tends to hold a drop of a liquid in a spherical shape.

Surfactants interfere with hydrogen bonding reducing surface tension.

This attraction between water molecules slows the tendency of water evaporation.

Water in solid state:Solid ice is less dense than liquid water,

thus it floats, making it one of the few solids that floats on its own liquid.

Why? Hydrogen bonds hold the water molecules in place in the solid phase, when ice melts, the water molecules pack closer together making liquid water more dense.

This is important for organisms living in a pond. A layer of ice on the top of a pond prevents water beneath to freeze completely.

Classwork: surfactants activity

Heterogeneous systems Objectives:1. Distinguish between a suspension and a

solution2. Identify the characteristics of a colloid.

Suspensions: a mixture from which particles settle out upon standing.Have very large particlesCan be filteredEx. Muddy water some medicines (antibiotics)

ColloidsHave medium sized particlesCan not be filtered.Many colloids are cloudy or milky in

appearance.Show Tyndall effect (the path of light is

visible)

Types of colloidsColloid type Dispersion

mediumDispersed substance

Examples

Aerosol Gas Liquid

Aerosol Gas Solid

Liquid Gas

Liquid Liquid

Liquid Solid

Solid Gas

Solid emulsion

Solid Liquid

Solid Solid

Classwork: Complete the table on the last slide, giving examples for the different types of colloids.

SolutionsObjectives:

Distinguish between a solvent and a soluteDescribe what happens in the solution processExplain what electrolytes are.

DefinitionsSolution - Solution - homogeneous mixture

Solvent Solvent - present in greater amount

Solute Solute - substance being dissolved

Solution = Solute + SolventSolute - gets dissolved Solvent - does the dissolving

Aqueous (water)Tincture (alcohol)Amalgam (mercury)Organic

Polar Non-polar

Dental filling

Types of Solutions

Solute Solvent Solution

Gaseous Solutions

gas

liquid

gas

gas

air (nitrogen, oxygen, argon gases)

humid air (water vapor in air)

Liquid Solutions

gas

liquid

solid

liquid

liquid

liquid

carbonated drinks (CO2 in water)

vinegar (CH3COOH in water)

salt water (NaCl in water)

Solid Solutions

liquid

solid

solid

solid

dental amalgam (Hg in Ag)

sterling silver (Cu in Ag), alloys

Charles H.Corwin, Introductory Chemistry 2005, page 369

Dissolving ProcessIn order to dissolve - the solvent

molecules must come in contact with the solute.

Stirring moves fresh solvent next to the solute.

The solvent touches the surface of the solute.

Smaller pieces increase the amount of surface of the solute.

SolvationSolvation – Solvation – the process of dissolving:

solute particles are separated and pulled into solution

solute particles are surrounded by solvent particles

Dissolving of NaCl

Timberlake, Chemistry 7th Edition, page 287

HH

O

Na+

+

-- + -+

+

-

Cl-

+ -

+

hydrated ions

NaCl(s) + H2O Na+(aq) + Cl-(aq)

Cl-

ions

Na+

ions Water molecules

NaCl(s) + H2O Na+(aq) + Cl-(aq)

Cl-

ions

Na+

ions Water molecules

Pure water does not conduct an electric current

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

Source ofelectric power

Purewater

Ionic Solutions conduct a Current

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

Source ofelectric power

Free ionspresent in water

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

(a) Nonelectrolyte (b) Weak electrolyte (c) Strong electrolyte

Electrolytes

Timberlake, Chemistry 7th Edition, page 290

ElectrolytesElectrolytes - solutions that carry an electric current

NaCl(aq) Na+ + Cl- HF(aq) H+ + F-

strong electrolyte weak electrolyte nonelectrolyte

Electrolyte Normal range (mmol / L)

Excess Defiency

Sodium

Na+

135 - 145 Hypernatremia

(increased urine excretion; excess water loss)

Hyponatremia (dehydration; diabetes-related low blood pH; vomiting, diarrhea)

Potassium

K+

3.5 – 5.0 Hyperkalemia

(renal failure, low blood pH)

Hypokalemia

(gastointestinal conditions)

Hydrogen carbonate HCO3

-24 - 30 Hypercapina

(high blood pH; hypoventilation)

Hypocapnia

(low blood pH; hyper-ventilation; dehydration)

Chloride

Cl-100 - 106 Hyperchloremia

(anemia, heart conditions, dehydration)

Hypochloremia

(acute infections; burns; hypoventilation)

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

(a) Cells in dilute salt solution (b) Cells in distilled water (c) Cells in concentrated salt solution

Isotonic Hypotonic Hypertonic

Classwork: go to my wikiRead article “The Quest for a Clean Drink”Answer the questions.Webquest

Properties of SolutionsOBJECTIVES:

Identify the factors that determine the rate at which a solute dissolves.

Identify the factors that determine the mass of solute that will dissolve in a given mass of solvent.

Solution formation The “nature” (polarity, or composition) of

the solute and the solvent will determine…1. Whether a substance will dissolve2. How much will dissolve

Factors determining rate of solution...1. stirring (agitation)2. surface area the dissolving particles3. temperature

1. Stirring (agitation) moves fresh solvent into contact with the solute.

2. Smaller pieces increases the amount of surface area of the solute.

3. Higher temperature makes the molecules of the solvent move faster and contact the solute harder and more often.

– Speeds up dissolving.• Higher Temperature ALSO Usually

increases the amount that will dissolve (an exception is gases ).

Solubility- is the maximum amount of substance that will dissolve at a specific temperature. The units for solubility are:

grams of solute/100 grams solvent1) Saturated solution- Contains the

maximum amount of solute dissolved. NaCl = 36.0 g/100 mL water

2) Unsaturated solution- Can still dissolve more solute (for example 28.0 grams of NaCl/100 mL)

3) Supersaturated- solution that is holding (or dissolving) more than it theoretically can; a “seed crystal” will make it crystallize. Very unstable.

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute

dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

increasing concentration

a. The solubility of the KNO3 increases as the temperature increases.b. Yb2(SO4)3 shows a decrease in solubility as the temperature increases, and NaCl shows the least change in solubility as temperature changes.c. Only a negligible amount of NaCl would go into solution, if any.

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

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

gases

solids

a) 80g NaNO3 at 45C. The solution is ? unsaturated

b) 100g NaNO3 at 45C. The solution is ?

c) 120g NaNO3 at 45C. The solution is ?

d) How much more NaNO3 can you add to a solution with 40g of NaNO3 at 45C until it becomes saturated?

saturated

supersaturated

60 g

LiquidsMiscible means that two liquids can dissolve in each otherwater and antifreezewater and ethanol

Partially miscible- slightlywater and ether

Immiscible means they can’toil and vinegar

Solids tend to dissolve best when:

•They are heated•They are stirred•Crushed into smaller particles

Gases tend to dissolve best when:

•The solution is cold•The pressure is high

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

For gases in a liquid, the effect is the opposite of solids in liquidsAs the temperature goes up, gas solubility

goes downThink of boiling water bubbling?Thermal pollution may result from industry

using water for cooling

Solids dissolved in liquids Gases dissolved in liquids

To

Sol.

To

Sol.

As To , solubility As To , solubility

Solutions videoClasswork: solubility graph handout

Concentration of SolutionsObjectives:1. Solve problems involving the molarity of a

solution.2. Describe the effect of dilution on the total

moles of solute in solution.3. Define percent by volume and percent by

mass solutions.

Concentration is...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 soluteThese are qualitative descriptions

But, there are ways to express solution concentration quantitatively (NUMBERS!)

Concentrated vs. Dilute

Lots of solute, in a small amount of solvent.

Small amount of solute in a

large amount of solvent.

Notice how dark the

solutions appears.

Notice how light

the solution appears.

CONCENTRATED DILUTE

Making solutions1) Pour in a small amount of the

solvent, maybe about one-half

2) Then add the pre-massed solute (and mix by swirling to dissolve it)

3) Carefully fill to final volume.

Molarity: a unit of concentration

Molarity = n (moles of solute) V (liters of solution)•Abbreviated with a capital M, such as 6.0 M

This is the most widely used concentration unit used in chemistry.

- Page 481

1. How many grams of sodium chloride, NaCl, do you need to prepare 250.mL of a 0.5M NaCl solution? Molar mass NaCl= 58.5 g/mol

Molarity= n n= mass

V molar mass

n= Molarity x V = 0.5 mol 0.250L =0.125 mol

L

Mass= molar mass x n = 58.5 g 0.125 mol = 7.31 g

mol

2. What volume of a 1.0M NaCl solution can you prepare if you have 45.0g of NaCl? Molar mass NaCl = 58.5g / mol?

n= mass = 45.0 g mol = 0.769 mol

molar mass 58.5 g

Molarity (M) = n V= n = 0.769 mol L =0.769 L

V M 1.0 mol

Classwork : p 54 # 19-21

Percent solutions can be expressed by a) volume or b) mass

Percent by volume: = Volume of solute

x 100 Volume of solution

indicated %(v/v)Vsolution= Vsolute + Vsolvent

msolution= msolute + msolvent

Percent by mass: = Mass of solute(g) x 100

Volume of solution (mL)Indicated %(m/v)More commonly used

• Another way to do mass percentage is as mass/mass:

Percent by mass: = Mass of solute(g) x 100 Mass of solution (g)

– Indicated %(m/m)

1) 4.8 g of NaCl are dissolved in 82 mL of solution. What is the percent of the solution?

% (m/V) = mass solute x100 = 4.8 g x 100 = 5.85%

volume solution 82 mL

2) How many grams of salt are there in 52 mL of a 6.3 % solution?

Mass solute = %(m/v) x volume solution = 6.3 x 52 = 3.28 g

100 100

3. You mix 25.0 g of salt with 225g of water. What is the %(m/m) concentration of the solution?

%(m/m) = mass solute x 100

(mass solute + mass solvent)

%(m/m) = 25.0 x 100 = 10%

(25.0 + 225.0)

Classwork: percent composition handout

Dilution• Adding water to a solution will reduce the

number of moles of solute per unit volume• but the overall number of moles remains the

same!• Think of taking an aspirin with a small glass

of water vs. a large glass of water• You still have one aspirin in your body,

regardless of the amount of water you drank, but a larger amount of water makes it more diluted.

DilutionThe number of moles of solute in

solution doesn’t change if you add more solvent!

The # moles before = the # moles after

Formula for dilution: M1 x V1 = M2 x V2

M1 and V1 are the starting concentration and volume; M2 and V2 are the final concentration and volume.

Stock solutions are pre-made solutions to known Molarity.

1. You need to prepare 500. mL of a 0.5M KCl solution. What volume of a 2.0 M KCl solution do you need?

M1 x V1 = M2 x V2 M1=2.0M V1= ? M2= 0.5M V2= 500.mL

V1= M2V2 = 0.5M 500mL = 125 mL

M1 2.0M

2. You add 200 mL of water to 50.0 mL of a 3.0M NaCl solution. What is the new concentration of the solution?

M1 x V1 = M2 x V2 M1=3.0M V1= 50.0mL M2= ? V2= 250.mL

M2= M1V1 = 3.0M 50.0mL = 0.6 M

V2 250mL

Classwork: Dilutions handout

Colligative Properties of SolutionsOBJECTIVES:

Identify three colligative properties of solutions.

Explain why the vapor pressure, freezing point, and boiling point of a solution differ from those properties of the pure solvent.

Solve problems related to the molality and mole fraction of a solution.

Describe how freezing point depression and boiling point elevation are related to molality.

Colligative Properties -These depend only on the

number of dissolved particles -Not on what kind of particle -Three important colligative

properties of solutions are:1) Vapor pressure lowering2) Boiling point elevation3) Freezing point lowered

Glucose will only have one particle in solution for each one particle it starts with.

NaCl will have two particles in solution for each one particle it starts with.

CaCl2 will have

three particles in solution for each one particle it starts with.

Colligative Properties

Some particles in solution will IONIZE (or split), while others may not.

Vapor Pressure is LOWERED1) Surface area is reduced, thus less

evaporation, which is a surface property2) The bonds between molecules keep

molecules from escaping. So, in a solution, some of the solvent is busy keeping the solute dissolved.

This lowers the vapor pressure Electrolytes form ions when they are

dissolved, making more pieces. NaCl Na+ + Cl- (this = 2 pieces) More pieces = a bigger effect

Boiling Point is ELEVATEDThe vapor pressure determines the boiling

point. (Boiling is defined as when the vapor pressure of liquid = vapor pressure of the atmosphere).

Lower vapor pressure means you need a higher temperature to get it to equal atmospheric pressure

Salt water boils above 100ºCThe number of dissolved particles

determines how much, as well as the solvent itself.

Freezing Point is LOWEREDSolids form when molecules make an

orderly pattern called “crystals”The solute molecules break up the orderly

pattern. Makes the freezing point lower.Salt water freezes below 0ºC

How much lower depends on the amount of solute dissolved.

The addition of a solute would allow a LONGER temperature range, since freezing point is lowered and boiling point is elevated.

Molality (abbreviated m)

a new unit for concentrationm = Moles of solute

kilogram of solvent

Mole fractionThis is another way to express

concentrationIt is the ratio of moles of solute to total

number of moles of solute plus solvent moles solute

(moles of solute + moles of solvent)The sum of the mole fractions of all the

components of a solution equals one. There is no unit for mole fraction.

X =

Ex.1 Calculate the molality of a solution made by dissolving 45.0g of glucose, C6H12O6, in 500.0 g of water.

m = Moles of solute kilogram of solvent

Moles of solute = 45.0g 1 mol = 0.25 mol 180g m = moles of solute = 0.25 mol = 0.5 m kg of solvent 0.5 kg

Ex. 2 What are the mole fractions of glucose and water in a solution made of 7.59g of glucose, C6 H12O6 dissolved in 125 g of water?

Molar mass glucose : 180.0g/molMolar mass water: 18.0g/mol

Mol glucose= 7.59 g mol = 0.0422mol mol water= 125g mol = 6.94 mol 180.0g 18.0g

Xglucose = moles solute = 0.0422 = 0.00605 (moles solute + moles solvent (0.0422 + 6.94)

Xwater = 1 – 0.00605= 0.994

CW p 144 # 1-3, 145 # 4-5