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
• Formula FM(g/mol) MP (oC) BP (oC)
• CH4 16• NH3 17• H2O 18 = 18 g/mol ± 11%• HF 20• Ne 20
Is this special?
• Consider Table 17.1—MP and BP of molecules of similar size (and HF): p 480
• Formula FM(g/mol) MP (oC) BP (oC)
• 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?
• Consider Table 17.1—MP and BP of molecules of similar size (and HF): p 480
• Formula FM(g/mol) MP (oC) BP (oC)
• 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
For the covalent hydrogen compounds of the second period:
Water!
Is this special?
• Consider Table 17.1—MP and BP of molecules of similar size (and HF): p 480
• Formula FM(g/mol) Liquid Range• CH4 16 19• NH3 17 45• H2O 18 100• HF 20 103• Ne 20 3
For the covalent hydrogen compounds of the second period:
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?
Why do particles stick together?
• In order, from weakest to strongest:
Dispersion Forces
Dipole Interactions
Hydrogen Bonding
Ionic Bonds
Metallic Bonds
Covalent Bonds
Why do particles stick together?
• 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
Why do particles stick together?
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
Why do particles stick together?
• Watch out for a trick question.
Why do particles stick together?
• 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?
• Consider Table 17.1—MP and BP of molecules of similar size (and HF)
• Formula Type of substance• CH4
• NH3
• H2O• HF• Ne
Is this special?
• Consider Table 17.1—MP and BP of molecules of similar size (and HF)
• 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?
• Consider Table 17.1—MP and BP of molecules of similar size (and HF)
• 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?
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).
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.
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..
• The ionic bonds in NaCl are stronger than hydrogen bonds between HCl molecules
What kind of IM forces?
• barium
• chlorine
• tin (II) chloride
• sulfur dioxide
• solid sulfur
• helium
• nitrogen dioxide• iron• sodium oxide• iodine• barium sulfide• sulfuric acid
Rank in order of strength of IM forces.
• barium
• chlorine
• tin (II) chloride
• sulfur dioxide
• solid sulfur
• helium
• nitrogen dioxide• iron• sodium oxide• iodine• barium sulfide• sulfuric acid
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
• tin (II) chloride
• sulfur dioxide
• solid sulfur
• helium
• nitrogen dioxide• iron• sodium oxide• iodine• barium sulfide• sulfuric acid
List in order of MP (low to high)
• barium
• chlorine
• tin (II) chloride
• sulfur dioxide
• solid sulfur
• helium*
• nitrogen dioxide• iron• sodium oxide• iodine• barium sulfide• sulfuric acid
Nonpolaronly dispersion forces. The smallest of the nonpolar substances Lowest MP
List in order of MP (low to high)
• barium*
• chlorine
• tin (II) chloride
• 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
Solutions: A solution is…
• --a homogeneous mixture
Components are mixed at a molecular level.
Any two samples of the same solution will have identical proportions of the components
Solutions: A solution is…
• --a solute dissolved in a solvent
Solutions: A solution is…
• --a solute dissolved in a solvent
Usually there is more solvent in a solution
The solvent is usually a liquid or a gas
Solutions: A solution is…
• --a physical combination of indefinite proportions
Solutions: A solution is…
• --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
What is the name and % water in CaCl2•2H20
• Name: calcium chloride dihydrate
• % water
What is the name and % water in CaCl2•2H20
• Name: calcium chloride dihydrate
• % water = mass water x 100%
mass total
What is the name and % water in CaCl2•2H20
• Name: calcium chloride dihydrate
• % water = mass water x 100%
mass total
= 2 x 18.02g x 100%
(40.08+2x35.45+2x18.02)
What is the name and % water in CaCl2•2H20
• Name: calcium chloride dihydrate
• % water = mass water x 100%
mass total
= 2 x 18.02g x 100%
(40.08+2x35.45+2x18.02)
= (36.04/147.02)x100%
What is the name and % water in CaCl2•2H20
• Name: calcium chloride dihydrate
• % water = mass water x 100%
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.)
What is the extent of hydration…
…of lead (II) acetate if the crystal has 14.2% water?
1)% water x100%=mass water= 14.2g water
mass total 100 g total
What is the extent of hydration…
…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.
What is the extent of hydration…
…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
What is the extent of hydration…
…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
• FM= 325.33 g/mol
What is the extent of hydration…
2) Convert to moles:
What is the extent of hydration…
2) Convert to moles:
14.2g H2O x 1mol/18.02g = .788 mol
85.8 g Pb(C2H3O2)2.x1mol/325.33g=.264mol
What is the extent of hydration…
2) Convert to moles:
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
What is the extent of hydration…
2) Convert to moles:
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
What is the extent of hydration…
• … 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