1.2 Water: Life’s Solvent

Question 1

Water’s Importance?

Answer 1

• Universal solvent
• Approx. 60% of our bodies are water
• All cellular processes occur in water
• ALL LIVING THINGS contain water
• Simple in its structure and
  complex in its functions

Question 2

Why are water molecules special?

Answer 2

• Size
• Shape
• Polar structure
• Ability to associate together via hydrogen bonds

Question 3

Properties of Water:

Answer 3

1. Cohesion
2. Adhesion
3. High Specific Heat Capacity
4. High Specific Heat Of Vaporization
5. Solid Water is Less Dense than Liquid Water

Question 4

1. Cohesion

Answer 4

*Force of attraction between like molecules

• Water molecules form hydrogen bonds with each other
• This results in surface tension and allows small insects/spiders to walk on water

Question 5

2. Adhesion

Answer 5

*Force of attraction between different molecules

• Water molecules may also form hydrogen bonds
  with other polar molecules
• Helps plants transport water (sticks to xylem)
• Allows water to dissolve polar substances

Question 6

3. High Specific Heat Capacity

Answer 6

Water absorbs large amounts of thermal energy
when heated (also releases large amounts of thermal
energy as it cools)

*Helps organisms maintain a constant body temperature
(holds heat)

Question 7

High Specific Heat Of Vaporization

Answer 7

Water absorbs large amounts of heat as it evaporates

• Many organisms cool themselves through evaporation
  (sweating)

Question 8

5. Solid Water is Less Dense than Liquid Water

Answer 8

*As water cools the water molecules form a lattice structure that spreads the molecules farther apart thus lowering density

• the result is that ICE FLOATS!
• prevents ice from killing aquatic organisms

*Snow has a very high insulation value
* keeps critters warm in winter

Question 9

Water molecules are
_____ and _________ _______

Answer 9

Water molecules are SMALL and STRONGLY POLAR

*They surround other ions/molecules and prevent them from reforming

Question 10

*Hydrophilic

Answer 10

polar substances that are
attracted to water (ex. Salt)

Question 11

*Hydrophobic

Answer 11

non-polar substances that
are not attracted to water (ex. Oil)

Question 12

Properties of Acids

Answer 12

H+ ions are responsible for acidity

Taste Sour, Conduct Electricity, Turns Blue Litmus paper Red

Question 13

Properties of Bases

Answer 13

OH- ions are responsible for alkalinity (basic)

Taste Bitter, Feel Slippery, Conducts Electricity, Turns Red Litmus paper Blue

Question 14

Strong Acids and Bases

Answer 14

*Strong Acid/Base – completely dissociates in water
* (ex. 100% of HCl dissociates)

Question 15

Weak Acids and Bases

Answer 15

Weak Acid/Base – only a small percentage of the molecules dissociate in water
* (ex. 10% of Ammonia, a base, dissociates in water)

Question 16

Buffers

Answer 16

Buffer:

A chemical that can change the pH by accepting or releasing H+
ions

Question 17

How do Buffers work

Answer 17

If excess H+ ions, the buffer combines with the H+ ions so they are no longer free in the solution

If low H+ ions, buffer can release H+ ions into solution to increase their concentration

Question 18

Example of a Buffer

Answer 18

Since most weak acids/weak bases have reversible reactions they often act as buffers

These buffers release or absorb H+ and OH- ions as necessary