water --a special liquid for a special set of students

Water

--a special liquid for a special set of students

Physical Parameters of Water

• Formula

• FM

• Shape

• Polar?

• Density

Physical Parameters of Water

• Formula H2O

• FM 18.02 g/mol

• Shape bent, 104.5o

• Polar? Yes

• Density 1.00 g/ml

Thermal characteristics of Water

• MP

• BP

• C

• Hfus

• Hvap

Thermal characteristics of Water

• MP 0.0oC

• BP 100.0oC

• C 4.18 J/goC

• Hfus 6 kJ/mol, 334 J/g

• Hvap 41 kJ/mol, 2300 J/g

Is this special?

• Consider Table 17.1—MP and BP of molecules of similar size (and HF)

• Formula FM(g/mol) MP (oC) BP (oC)

• CH4

• NH3

• H2O• HF• Ne

Is this special?

• Consider Table 17.1—MP and BP of molecules of similar size (and HF): p 480


• CH4 16• NH3 17• H2O 18 = 18 g/mol ± 11%• HF 20• Ne 20

Is this special?



• CH4 16 -183• NH3 17 -78• H2O 18 0 • HF 20 -83• Ne 20 -249

For the covalent hydrogen compounds of the second period:

Melting points

-300

-250

-200

-150

-100

-50

0

0 2 4 6

Substance #

Mel

tin

g p

oin

t

Series1

Water!

Is this special?



• CH4 16 -183 -164• NH3 17 -78 -33• H2O 18 0 100• HF 20 -83 20• Ne 20 -249 -246

Boiling points

-300-250-200-150-100-50

050

100150

0 2 4 6

Substance #

Bo

ilin

g p

oin

t

Series1


Water!

Is this special?


• Formula FM(g/mol) Liquid Range• CH4 16 19• NH3 17 45• H2O 18 100• HF 20 103• Ne 20 3


Liquid Ranges

0

20

40

60

80

100

120

0 2 4 6

Substance #

Liq

uid

ran

ge

Series1

Water!

Consider KMT:

• Melting occurs when particles have enough motion to escape their solid structure

Consider KMT:

• Melting occurs when particles have enough motion to escape their solid structure

• A substance whose particles cling together better has a higher melting point

Consider KMT:

• Boiling occurs when particles have enough motion to escape their liquid neighbors

Consider KMT:

• Boiling occurs when particles have enough motion to escape their liquid neighbors

• A substance whose particles cling together better has a higher boiling point

Consider KMT:

• The liquid range is all of those temperatures where the particles move around each other, but are unlikely to escape

Consider KMT:

• The liquid range is all of those temperatures where the particles move around each other, but are unlikely to escape

• A substance whose particles cling together better, even while moving, has a larger liquid range.

Therefore…

• Water molecules stick together very well—in a solid, and as a liquid.

Why do molecules stick together?

Why do molecules stick together?

• Attractions between molecules are called intermolecular forces (IM forces)

• Different types of substances have different types of IM forces

• Some forces are stronger than others.

Non-polar molecules…

Show dispersion forces

• very weak

• very brief, small charge imbalances due to the motion of electrons.

• They unbalance and attract their neighbors.

Polar molecules…

Show dipole interactions

• fairly weak.

• permanent, small charge imbalances due to the polarity of their bonds.

• They attract their polar neighbors.

(But, not all polar bonds are created equal)

• When hydrogen is the less electronegative end of a polar bond:

+ -

H Cl--the hydrogen is more positive

--it is losing custody of its last electron

Polar molecules with hydrogen…

Show hydrogen bonding

• strongest of the weak bonds.

• permanent, larger charge imbalances than other polar bonds.

• They attract their polar neighbors better.

…and if it’s not weak…

Strong IM forces include…

Ionic bonds (in ionic compounds)

Metallic bonds (in pure metals and alloys)

Covalent bonds (in covalent network solids)

(None of these particles are molecules, but they are still called intermolecular forces.)

Why do particles stick together?


• In order, from weakest to strongest:

Dispersion Forces

Dipole Interactions

Hydrogen Bonding

Ionic Bonds

Metallic Bonds

Covalent Bonds


• In order, from weakest to strongest:

Dispersion Forces —between non-polar molecules

Dipole Interactions —between polar molecules

Hydrogen Bonding -between polar molecules w/H

Ionic Bonds —between ions

Metallic Bonds —between metal atoms

Covalent Bonds —in a network solid


If you are given a substance:

• --describe the type of substance

• --describe the strongest IM force between the particles

• --you may be asked to compare it to another substance

What kind of substance?

• barium

• chlorine

• tin (II) chloride

• sulfur dioxide

• solid sulfur

• helium

• nitrogen dioxide• iron• sodium oxide• iodine• barium sulfide• sulfuric acid


• Watch out for a trick question.


• Watch out for a trick question.

--Ready?

Quiz

Q: What holds water together?

Quiz

Q: What holds water together?

A: HA! It’s a trick question!

There are TWO answers, both important.

Answer 1:

• Polar covalent bonds between the hydrogen and oxygen atoms hold the atoms together as water molecules

• Answer 2:

• Hydrogen bonding, due to the hydrogen being the less electronegative atom of a polar covalent bond, attracts a water molecule to its neighbors as a liquid or a solid.

(Please notice that the first answer leads to the second.)

Is this special?


• Formula Type of substance• CH4

• NH3

• H2O• HF• Ne

Is this special?


• Formula Type of substance• CH4 non-polar covalent molecule• NH3 polar covalent molecule• H2O polar covalent molecule• HF polar covalent molecule• Ne non-polar individual atoms

Is this special?


• Formula Type of IM Forces• CH4 dispersion forces• NH3 hydrogen bonding• H2O hydrogen bonding• HF hydrogen bonding• Ne dispersion forces

Which has stronger intermolecular forces, NaCl or HCl?


• NaCl: ionic compound (Na+ and Cl- ions) HCl: polar covalent molecule (linear, with H in a polar bond).



• NaCl: held together by ionic bonds

HCl molecules: attracted to each other by hydrogen bonds.



• NaCl: held together by ionic bonds

HCl molecules: attracted to each other by hydrogen bonds..

• The ionic bonds in NaCl are stronger than hydrogen bonds between HCl molecules

What kind of IM forces?

• barium

• chlorine


• sulfur dioxide

• solid sulfur

• helium


Rank in order of strength of IM forces.

• barium

• chlorine


• sulfur dioxide

• solid sulfur

• helium


Compare N2 and CO

• What type of substance?

• What type of IM forces

• Which is stronger?

• What will this do to the MP and BP?

There is an overlap.

• The strongest dispersion forces are stronger than average dipole interactions

• In general, a larger molecule has stronger dispersion forces.

• There is a big overlap between ionic and metallic bonds.

“’The time has come’, the walrus said…”

• The stronger the IM forces, the higher the:

MP, BP, Hfus, Hvap, C, surface tension, cohesion, viscosity,

strength and hardness of the solid…

…etc. Usually.

List in order of MP (low to high)

• barium

• chlorine


• sulfur dioxide

• solid sulfur

• helium



• barium

• chlorine


• sulfur dioxide

• solid sulfur

• helium*


Nonpolaronly dispersion forces. The smallest of the nonpolar substances Lowest MP


• barium*

• chlorine


• sulfur dioxide

• solid sulfur

• helium*

• nitrogen dioxide• iron*• sodium oxide• iodine• barium sulfide• sulfuric acid

Metalsmetallic bonds.Highest MP

Nonpolaronly dispersion forces. The smallest of the nonpolar substances Lowest MP

Solutions: A solution is…

• --a homogeneous mixture


• --a homogeneous mixture

Components are mixed at a molecular level.

Any two samples of the same solution will have identical proportions of the components


• --a solute dissolved in a solvent


• --a solute dissolved in a solvent

Usually there is more solvent in a solution

The solvent is usually a liquid or a gas


• --a physical combination of indefinite proportions


• --a physical combination of indefinite proportions

Dissolving is a physical (not chemical) process

Two solutions can have different proportions

The components retain their own chemical and physical properties

Oh, yeah…

• With two gasses or two liquids that dissolve in each other (miscible liquids), it really doesn’t matter which one you call the solvent

• When something is dissolved in water, we say that it is aqueous (aq).

Oil and water don’t mix.

Why not?

“Like dissolves like”

• Water is a polar solvent, oil is a non-polar substance.

• They are not alike

Non-polar solvents dissolve non-polar solutes

Polar solvents dissolve polar and ionic solutes

Metallic solvents dissolve metallic solutes.

“Like dissolves like”

Does it dissolve?

1) CH3OH/H20

2) KBr/H2O

3) CCl4/H2O

4) S8/H2O

5) Hg/H2O6) Ag/Hg

7) S8/CCl48) NaCl/KBr

Does it dissolve?

1) CH3OH/H20—polar/polar =YES

2) KBr/H2O

3) CCl4/H2O

4) S8/H2O

5) Hg/H2O6) Ag/Hg

7) S8/CCl48) NaCl/KBr

Does it dissolve?

1) CH3OH/H20 —polar/polar =YES

2) KBr/H2O —ionic/polar =YES

3) CCl4/H2O —nonpolar/polar =NO

4) S8/H2O —nonpolar/polar =NO

5) Hg/H2O —metallic/polar =NO6) Ag/Hg —metallic/metallic =YES

7) S8/CCl4 —nonpolar/nonpolar=YES8) NaCl/KBr —ionic/ionic(if melted)=YES

How?

• Liquids that dissolve mix. Molecules mingle

• All gasses just mix. Molecules move freely

• Particles on the surface of a solid get surrounded by solvent particles (solvation) and lifted out of the solute.

Water is special.

• The attraction of the polar water molecules lifts polar molecules and individual ions out of solids.

• Ions dissociate, making an electrolyte solution

Remember MgSO4•7H2O?

• Each formula unit of MgSO4 is surrounded by 7 water molecules in the crystal—the water of hydration.

• You drove off the water by heating the solid.

• Many ionic compounds make hydrated crystals. Some have over half of their mass as the water of hydration

Remember MgSO4•7H2O?

• FM ≈24+32+4x16+7x2x1+7x16≈ 246 g/mol

• Name: magnesium sulfate heptahydrate

Meaning “seven”Meaning “water”

Three Tasks: Hydrates

• Write the correct name and formula for hydrated salts

• From a formula, calculate the % water in the solid.

• From a % composition by mass, find the number of waters of hydration.

What is the name and % water in CaCl2•2H20

• Name:

• % water


• Name: calcium chloride dihydrate

• % water



• % water = mass water x 100%

mass total




mass total

= 2 x 18.02g x 100%

(40.08+2x35.45+2x18.02)




mass total

= 2 x 18.02g x 100%

(40.08+2x35.45+2x18.02)

= (36.04/147.02)x100%




mass total

= 2 x 18.02g x 100%

(40.08+2x35.45+2x18.02)

= (36.04/147.02)x100%

= 24.51%

What is the formula and % water in iron (III) chloride hexahydrate?

What is the extent of hydration…

1) Use the % water to find masses of water and salt in 100 g

2) Convert to moles, using formula masses

3) Find a mole ratio, water/salt

4) (Write a formula. Name it.)


…of lead (II) acetate if the crystal has 14.2% water?

1)% water x100%=mass water= 14.2g water

mass total 100 g total





So, the crystal has 14.2 g water for every (100-14.2=) 85.8 g lead (II) acetate.






• Lead (II) acetate= Pb(C2H3O2)2






• Lead (II) acetate= Pb(C2H3O2)2

• FM= 325.33 g/mol


2) Convert to moles:



14.2g H2O x 1mol/18.02g = .788 mol

85.8 g Pb(C2H3O2)2.x1mol/325.33g=.264mol



14.2g H2O x 1mol/18.02g = .788 mol

85.8 g Pb(C2H3O2)2.x1mol/325.33g=.264mol

3) --and the ratio is

.788molH2O / .264molPb(C2H3O2)2 ≈ 3



14.2g H2O x 1mol/18.02g = .788 mol

85.8 g Pb(C2H3O2)2.x1mol/325.33g=.264mol

3) --and the ratio is

.788molH2O / .264molPb(C2H3O2)2 ≈ 3

4) Pb(C2H3O2)2•3H2O is

lead (II) acetate trihydrate


• … of NiCl2•xH20 if the solid is 45.5% water?

Colloids and emulsions

• Colloids and emulsions are (barely) heterogeneous mixtures

• The particles are just barely too large to be called “molecular sized”

• Colloids and emulsions do not separate themselves, but appear cloudy or opaque

Suspensions

• If the particles are too large to dissolve or form a colloid, they can still be suspended in a fluid.

• Suspensions settle out eventually.

Define:

• Melting point Boiling point

• Heat of vaporizationHeat of fusion

• Specific heat capacity Adhesion

• Cohesion Surface tension

• Density Solubility

• Solution Solute

• Solvent Dissociation

water --a special liquid for a special set of students

Documents

special liquid

bp of molecules

liquid neighborsconsider

similar size

thereforewater molecules

liquid neighborsa substance

larger liquid range

escapeconsider kmt