2.2 Properties of Water

H2O

# of Protons

# of Electrons

Atomic Mass

10

10

18

The Water Molecule

Polarity – water is polar because of an uneven distribution of electrons between oxygen and hydrogen.

Covalent bonds between oxygen and hydrogen.

Electrons hang out more often near the oxygen atom.

Slightly Negative (-)

Slightly Positive (+)

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 attractTo glass molecules

And form a meniscus

Water compounds attract To one another-

causes water to “bead”

ADHESION

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.

SolutionsAll 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)

Animation

Water is the universal solvent!

(Polar molecules dissolve polar molecules)

Acids and Bases

Acidity and Alkalinity is measured by the concentration of . . .

• Hydrogen Ions H+

• Hydroxide Ions OH-

Animation

• Produce H+ ions in solution

• If H+ > OH- then the solution is acidic.

Acids

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 AlkalinitypH 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 7Try 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. Shampoo

2. Lemon juice

3. Drain cleaner

4. Milk

5. Bleach

6. Soda (pop if you’re from Pittsburgh)

7. Water

pH Laboratory

1. Shampoo (5-7)

2. Lemon juice (2)

3. Drain cleaner (14)

4. Milk (7)

5. Bleach (12)

6. Soda (pop if you’re from Pittsburgh) (3)

7. Water (7)

LITMUS PAPER:

Blue turns Red = Acid

Red turns Blue = Base

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!