2.2 Properties of Water
H2 O
# of Protons
10
# of Electrons
Atomic Mass
10
18
The Water Molecule
Slightly
Positive (+)
Electrons hang
out more often
near the oxygen
atom.
Covalent bonds
between oxygen
and hydrogen.
Slightly Negative (-)
Polarity – water is polar because of an uneven distribution
of electrons between oxygen and hydrogen.
Hydrogen Bonds
• Because of their partial charges water molecules
become attracted to each other by weak hydrogen bonds
•Hydrogen bonds are not as strong as ionic or covalent bonds
•Cohesion – attraction between molecules of the same substance
•Adhesion - attraction between molecules of different substances.
COHESION
Water compounds attract
To one anothercauses water to “bead”
ADHESION
Water compounds attract
To glass molecules
And form a meniscus
Capillary Action
• Def – water
climbing up a small
tube because of the
adhesion to the
sides and the
cohesion between
water molecules.
Other Unique Properties of Water
• High specific heat - water will absorb lots
of heat energy with a minimal
temperature increase
• High heat of vaporization – water will
absorb lots of heat energy with minimal
evaporation.
Other Unique Properties of Water
• Expansion on freezing – water forms a
crystalline structure that expands and is
less dense than its liquid state
Other Unique Properties of Water
• High surface tension – hydrogen bonds
hold water together tightly, so the waters
surface acts like a membrane
Solutions and Suspensions
Mixture – a material that consists of 2 or more
elements or compounds physically mixed
together but are not chemically combined.
Solutions
All the components of a solution are evenly
distributed throughout the solution.
Solute – the substance being dissolved (salt)
Solvent – the substance in which the solute is
dissolved. (water)
Water is the
universal solvent!
(Polar molecules
dissolve polar
molecules)
Animation
Acids and Bases
Animation
Acidity and Alkalinity is measured by the
concentration of . . .
• Hydrogen Ions H+
• Hydroxide Ions OH-
Acids
• Produce H+ ions in solution
• If H+ > OH- then the solution is acidic.
Bases
• Produce OH- ions in solution
• If OH- > H+ then the solution is basic
Neutral Solution
• If OH- = H+ then the solution is neutral
Measuring Acidity or
Alkalinity
pH Scale:
(power of Hydrogen) as in Hydrogen ions
1. Use the structure of a water molecule to explain
why it is polar.
2. Why is water such a good solvent?
3. What is the difference between a solution and a
suspension?
4. How do hydrogen bonds between water
molecules occur?
5. How does the body counteract a drop in blood
pH during strenuous exercise?
6. If a strong acid is dissolved in pure water will the
pH of the solution be greater or less than 7?
Water Chemistry
1. Please draw the structure of a water molecule
(H2O).
2. Label the charges on the molecule that make it
polar (negative and positive ends).
3. See if you can connect the water molecule that
you drew to two other molecules of water using
hydrogen bonds.
4. Can you think of any unique properties that
water displays?
Water Chemistry
1. Explain why water is “polar” in your own words.
2. Explain capillary action in your own words.
3. Explain surface tension in your own words.
1. pH = the negative logarithm of the hydrogen ion (H+)
concentration.
2. pH of water = 1x10-7 or 7
Try this: pH .000000001 = ?
Or
pH .001 = ?
3. For each change of a pH unit the concentration of H+
ions differs by 10 times.
Try this: How many times more acidic is pH 2 compared
to pH 5?
pH Laboratory
1.
2.
3.
4.
5.
6.
7.
Shampoo
Lemon juice
Drain cleaner
Milk
Bleach
Soda (pop if you’re from Pittsburgh)
Water
pH Laboratory
1.
2.
3.
4.
5.
6.
7.
LITMUS PAPER:
Shampoo (5-7)
Blue turns Red = Acid
Lemon juice (2)
Red turns Blue = Base
Drain cleaner (14)
Milk (7)
Bleach (12)
Soda (pop if you’re from Pittsburgh) (3)
Water (7)
1. According to the scale, what substance is neutral?
2. What solution has an [H+] of 0.01?
3. Which substance produces the most OH- ions in
solution?
4. How many more times basic is pH 14 compared to
pH 11.
5. What substance has a hydrogen ion concentration of
1 X 10-4
Water Molecule
Properties of Water Quiz
Questions
• Use the Finish line Water Chemistry
section to develop 3 good questions about
water. Two of them should be multiple
choice and 1 should be a short answer
question.
• Submit for credit, you might see them on
the next quiz!