This document provides an overview of water and aqueous systems. It discusses the structure of the water molecule and how hydrogen bonding gives water its unique properties, including high surface tension and low vapor pressure. It describes how ice has a crystalline structure that is less dense than liquid water. The document also discusses homogeneous solutions and how solutes dissolve in solvents. It defines electrolytes and nonelectrolytes and how ionic compounds and polar molecules dissolve in water. Finally, it introduces heterogeneous systems like suspensions, colloids, and emulsions.

1. Chapter
15
Chapter 17 in your books
“Water and Aqueous Systems”

2. Section 15.1
Water and its Properties
OBJECTIVES:
• Explain the high surface tension and low vapor pressure of water in terms of the
structure of the water molecule and hydrogen bonding.
• Describe the structure of ice.
The Water Molecule: a Review
• Water is a simple tri-atomic molecule, H2O
• Each O-H bond is _____________________________, because of the high
electronegativity of the oxygen (N, O, F, and Cl have high values)
• bond angle of water = 105o
• due to the _______________________, the O-H bond polarities do not cancel. This
means: _________________________________________________________.
• Water’s bent shape and ability to hydrogen bond gives it many special properties!
• Water molecules are attracted to one another by dipole interactions
• This hydrogen bonding gives water:
a) its _________________________________________________, and
b) its _________________________________________________.
a) High Surface Tension?
• liquid water acts like it has a “skin”
– glass of water bulges over the top
• Water forms round drops
– spray water on greasy surface
• All because water hydrogen bonds.
Surface Tension
• One water molecule can hydrogen bond
to another because of this electrostatic attraction.
• Also, hydrogen bonding occurs with many other
molecules surrounding them on all sides.
• A water molecule in the middle of a solution is
pulled in all directions.
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3. • Not true at the surface.
• They are pulled down and to each side, not upward
since the water and air are not attracted to each other.
• This holds the molecules at the surface together tightly.
• This causes surface tension.
• Water drops are rounded, because all molecules on the
edge are pulled to the middle, not outward to the air!
• A drop has the least amount of surface area for any given
volume.
• Glass has polar molecules.
• Glass can also hydrogen bond.
• This attracts the water molecules.
• Some of them are pulled up a cylinder wall.
Meniscus
A meniscus is the _________________________________________________________
• Thus, water curves up along the sides of glass.
• This makes the meniscus, as in a graduated cylinder
• However, Plastics are non-wetting; there is no attraction to water
Surface tension
• All liquids have surface tension
– water is just __________________ than most others, due to the hydrogen
bonding present
• How can we decrease surface tension?
– Use a surfactant - surface active agent
– Also called a “wetting agent”, like detergent or soap (makes water
“wetter”)
– Interferes with hydrogen bonding
b) Low vapor pressure?
• Hydrogen bonding also explains water’s unusually low vapor pressure.
– It holds water molecules together, so they do not escape (evaporate)
easily, like gasoline or acetone does.
– This is a good thing, because lakes and oceans would evaporate very
quickly due to their large surface area!
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4. Ice
• Most liquids contract (get smaller) as they are cooled.
– They get more dense.
• When they change to solid, they are more dense than the liquid.
• Solid metals sink in their own liquid metal.
– But, ice ________________ in water.
• Why?
• Water becomes more dense as it cools, until it reaches about _________
– Then it becomes less dense by starting to expand
• Because as the molecules slow down, they arrange themselves into
__________________________________________________________
• These are held together by hydrogen bonds.
Liquid = random shaped arrangement Solid = honeycomb-shaped
arrangement
Ice
• Is 10% lower in density than liquid water.
• Water freezes from the top down.
– The layer of ice on a pond acts as an insulator for water below
• Why is ice less dense than liquid water?
– The structure of ice is a regular __________________________________
_______________________________________, arranged like a honeycomb.
• A considerable amount of energy is required to return water in the solid state to
the liquid (called melting)
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5. – The heat absorbed when 1 g of water changes from solid to liquid is _____
– This is the same amount of energy needed to raise the temperature of 1 g
of liquid water from 0 oC to 80 oC!
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6. Name _______________________________________ Date ______________________
15-1 Section Review
1. Describe the hydrogen bonding between molecules of water.
2. How is hydrogen bonding responsible for the high surface tension and low vapor
pressure of water?
3. What is the difference between the structure of liquid water and the structure of
ice? How does this explain why ice floats in water?
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7. Section 15.2
Homogeneous Aqueous Solutions
OBJECTIVES:
• Distinguish between a solvent and a solute.
• Describe what happens in the solution process.
• Explain why all ionic compounds are known as electrolytes.
• Demonstrate how the formula for a hydrate is written.
Solvents and Solutes
• Solution - a ________________________________________, that is mixed
molecule by molecule; made of:
1) a Solvent - ______________________________________________
2) a Solute - _______________________________________________
• Aqueous solution- a solution with __________________as the solvent.
• Particle size is less than 1 nm; ___________________be separated by filtration – Fig.
15.6, p.450
Parts of a Solution:
1. the Solute
A solute is the dissolved substance in a solution.
___________ in salt water ____________________ in soda drinks
_______________________________ in soda drinks
2. the Solvent
A solvent is the dissolving medium in a solution.
______________________ in salt water _______________________ in soda
Solutions
• Keep in mind that solutions do not have to contain water, but this is the type we are
studying in this chapter = ________________________________________
– Example: air is also a type of solution.
Concentrated vs. Dilute
Concentrated - Lots of ______________________, but little______________________
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8. Dilute - Lots of _______________________, but little _________________________
Aqueous Solutions
• Water _________________________ ionic compounds and polar covalent molecules
very well.
• The rule is: ___________________________________________
• Polar dissolves polar.
• Nonpolar dissolves nonpolar.
• Oil is nonpolar.
– Oil and water don’t mix.
• Salt is ionic- makes salt water.
The Solution Process
• Called _____________________________
• Water
1) ______________________________________________________________, and
2) _____________________________________________
• But, in some ionic compounds, the attraction _______________________________
is greater than the attraction ____________________________________________
– Barium sulfate and calcium carbonate do not dissolve in water!
• Solids _____________________________________ the attractive force of the
water molecules is stronger than the attractive force of the crystal.
• If not, the solids are ______________________________
• Water doesn’t dissolve nonpolar molecules (like oil) because the water molecules
can’t hold onto them.
• The water molecules hold onto other water molecules, and separate from the
nonpolar molecules.
• Nonpolars? No repulsion between them
Electrolytes and Nonelectrolytes
Electrolytes- __________________________________________________________
____________________________________________________________________
____________________________________________________________________
__
– all ionic compounds are electrolytes because they dissociate into ions
(they are also called “salts”)
• barium sulfate- will conduct when molten, but is insoluble in water!
• Do not conduct? = _____________________________________
– Most are molecular materials, because they ________________________
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9. • Not all electrolytes conduct to the same degree
– there are weak electrolytes, and strong electrolytes
– depends on: the degree of ionization
The ammeter measures the flow of electrons (current) through the circuit.
 If the ammeter measures a current and the bulb glows, then the solution
conducts.
 If the ammeter fails to measure a current and the bulb does not glow, the
solution is non-conducting.
• Strong electrolytes exist as nearly 100 % ions
• Weak electrolytes have only a fraction of the solute that exists as ions
Electrolyte Summary
• Substances that conduct electricity when dissolved in water, or molten.
• Must have charged particles that can _______________.
• Ionic compounds break into charged ions:
NaCl  Na1+ and Cl1-
• These ions can conduct electricity.
• Nonelectrolytes do not conduct electricity when dissolved in water or molten
• Polar covalent molecules such as methanol (CH3OH) don’t fall apart into ions
when they dissolve.
• Weak electrolytes don’t fall completely apart into ions.
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10. • Strong electrolytes do ionize completely.
Water of Hydration (or Water of Crystallization)
• Water molecules are chemically bonded to solid salt molecules (not in solution)
• These compounds have fixed amounts of water.
• The water can be driven off by heating:
+ heat
CuSO4 ∙5H2O ↔ CuSO4 + 5H2O
- heat
• Called _______________________________________________.
Hydrates
• Table 15.2, p.455 list some familiar hydrates
• Since heat can drive off the water, the forces holding the water are weak
• If a hydrate has a vapor pressure higher than that of water vapor in air, the
hydrate will _________________________ by losing ______________________
___________________________________________
• Some hydrates that have a low vapor pressure remove water from the air to form
higher hydrates- these are called ________________________________
– used as drying agents, or _________________________________
– packaged with products to absorb moisture
Sample Problem - Finding the Percent of Water in a Hydrate
Calculate the percent by mass of water in washing soda, sodium carbonate decahydrate
(Na2CO3 ∙ 10H2O).
Hydrates
• Some compounds are so hygroscopic, they become wet when exposed to normally
moist air - called ____________________________________
– remove sufficient water to dissolve completely and form solutions
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11. Name __________________________________________ Date ___________________
15-2 Homogenous Aqueous Solutions
Section Review
1. What is the significance of the statement. “Like dissolves like”? What does “like”
refer to?
2. Distinguish between an electrolyte and a nonelectrolyte. Distinguish between a
weak electrolyte and a strong electrolyte.
3. Identify the solvent and the solute in vinegar, a dilute aqueous solution of acetic
acid.
4. Write an equation showing how calcium chloride dissociates in water.
5. Which of the following substances dissolve to a significant extent in water?
Explain your answer in terms of polarity.
a. CH4
b. KCl
c. He
d. MgSO4
e. Sucrose
f. NaHCO3
6. What is the percent mass of water in CuSO4 ∙ 5H2O
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12. Section 15.3
Heterogeneous Aqueous Systems
OBJECTIVES:
• Distinguish between a suspension and a solution.
• Identify the distinguishing characteristics of a colloid.
Mixtures that are NOT Solutions:
1. __________________________________: mixtures that slowly settle upon standing.
Example: ___________________________________
– Particles of a suspension are __________________________in diameter
than 1000 nm.
– ___________ be separated by filtering
2.__________________________________: heterogeneous mixtures with particles
between the size of suspensions and true solutions (1-1000 nm)
• The colloid particles are the _______________________________________, and are
spread throughout the ____________________________________________
• The first colloids were glues. Others include mixtures such as gelatin, paint, aerosol
sprays, and smoke
• Table 17.5, p.491 (next slide) lists some common colloidal systems and examples
• Many colloids are cloudy or milky in appearance when concentrated, but almost clear
when dilute
– They _____________________ settle out
– They _____________________ be filtered out
• Colloids exhibit the ____________________________________________ - the
scattering of visible light in all directions.
– suspensions also show Tyndall effect
The Tyndall Effect
• Colloids and suspensions scatter light, making a beam visible, due to their
_________________ particle size.
• Solutions do not scatter light, because of their _______________ particle size.
Mixtures that are NOT Solutions
• Flashes of light are seen when colloids are studied under a microscope- light is
reflecting- called Brownian motion to describe the chaotic movement of the particles.
Observed by Robert Brown.
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13. • ______________________________- dispersions of a liquid in a liquid (2
immiscible liquids + an _________________________)
– an ______________________________________ is essential for
maintaining stability; it has ___________________________, and the
other end is ___________________________.
– oil and water not soluble; but with soap or detergent added, they will be.
• Oil + vinegar in dressing – are they soluble?
– What makes up Mayonnaise?
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14. Name _________________________________________ Date ____________________
15 – 3 – Heterogeneous Aqueous Systems
Section Review
1. What is the basis for distinguishing among solutions, colloids, and suspensions?
2. What is the Tyndall effect?
3. What is Brownian motion?
4. What are emulsions? How are emulsions stabilized?
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