Water

1
Water pH
Chapter 3 pgs. 35-42
2
Importance of Water
71 of Earths surface is ocean water 66 of
human weight Only common substance to exist in
three forms solid, liquid and gas
3
How does water work?

• Oxygen atom is attracted to the hydrogen atoms
• Resulting bonds are Hydrogen Bonds
• Individual hydrogen bonds are quite weak, but
  many working together are very strong
• Hydrogen bonds that give water its unique
  properties

4
Unique Properties of Water

• Solid form is less dense than the liquid
  
• form
• Absorbs lots of heat without much change
• in temperature
• Sticks to itself
• Sticks to other things

5
Unique Properties of Water
Ice floats for most substances, the solid form
is more dense than the liquid form and will sink.
But for water, the solid form is less dense than
the liquid form. Why is this important?
6
Unique Properties of Water
Water has great capacity to absorb and store
heat heat and temperature are not the same
things! For example Corningware glass pot vs.
aluminum pot of same weight were heated on two
stove burner. Which one would heat up faster?
The Corningware pot can absorb more heat without
changing in temperature much
7

• Specific heat the amount of energy required to
  raise the temperature of a substance by 1oC
• During the day in the summer, bodies of water
• (oceans and lakes) absorb heat from the sun
  and
• this keeps the surrounding air cooler
• At night and during the winter, bodies of water
• give up heat and this warms the surrounding
  air
• So why is the desert have such extreme day-time
  vs. night-time temperature changes?
• In our bodies, absorb heat in the summer from the
  sun without overheating in the winter we dont
  immediately freeze when we go outside

8
Just for fun facts

• It takes more energy to heat water than many
  other molecules because of hydrogen bonds.
• 1 calorie of energy will increase the temperature
  of 1 gram of water by 1 degree C
• It only takes 0.6 calories to increase 1 g of
  alcohol by 1 degree 0.2 calories to heat 1 g of
  table salt

9
Unique Properties of Water
Cohesion
Forms droplets
Cohesion produces surface tension, or the
tendency for the surface of the water to avoid
being broken.
10
Why is cohesion important?

• The strong hydrogen bonds of water allow water
  to be pulled up through the roots of a 100-meter
  tall tree

11
Unique Properties of Water
Water molecules can stick to other things, or at
least some other things For example glass,
paper, sugar, salt can mix with or stick to
water. Hydrophilic Those compounds that
do not interact with water such as salad oil,
teflon, car wax Hydrophobic
12

• Hydrophobic Molecules

• Hydrophilic Molecules

13
What are acids and bases?

• Examples of acids lemon juice, vinegar, tomatoes
• Acid
• Examples of bases ammonia, soap, oven cleaners
• Base
• Measure the degree of acidic or basic by the pH
  scale

14
pH Scale

• Neutrality (equal numbers of H and OH-) 7
• Acids below 7
• Bases above 7
• Each unit 10 fold change

1
11
7
4
14
15

• The higher the pH, the more
• basic the solution
• A solution that is basic is also
• referred to as an alkaline
• solution
• The lower the pH, the more
• acidic the solution

16
Example Vinegar has a pH of 3 If you add sodium
hydroxide (NaOH), what will happen to the pH of
your vinegar? If you add hydrochloric acid
(HCl)?
17
Why do we care about pH?

• Living organisms are sensitive to pH levels and
  an
• imbalance in pH can lead to DEATH!
• Organisms have developed ways of keeping pH
• within normal ranges using an acid-base
  buffering
• system
• Buffer substances that minimized change in pH

18
Just for fun facts

• The pH of our stomachs are around 1-2, so that
  
• foods can be broken down
• The optimal pH for healthy skin and scalp is
  around
• 5 slightly acidic for resistance to infection
  and
• diseases
• Soaps and shampoos are basic and thus can cause
• drying of the skin and scalp
• So when you see a pH-balanced shampoo or
• soap, the manufacturer has lowered the pH so
  its
• closer to normal skin pH