Water and Life

Video

H2O: The Molecule That Supports All of Life !  Water is the biological medium on Earth !  All living organisms require water more than any

other substance !  Most cells are surrounded by water, and cells

themselves are about 70-95% water !  The abundance of water is the main reason the

Earth is habitable

Hydrogen Bonds: Polar bonding between Hydrogen and an electronegative Atom

Hydrogen Bond

Hydrogen Bonds are very important in life

!  Weak bond, useful in stabilizing large biological molecules such as proteins

Properties of Water b. Hydrogen-bond lattice of ice a. Hydrogen-bond lattice of liquid water

Because of hydrogen bonding, water has a high specific heat

Hydrogen bonds in Water lead to Surface Tension / Cohesion

!  Forms at surface of water in contact with air

!  Hydrogen bonds resist stretching, giving surface strength

Cohesion Moderation of Temperature

!  Water has a high specific heat. Heat is absorbed when hydrogen bonds break and released when hydrogen bonds form.

40 miles

Santa Barbara 73°!

Los Angeles (Airport) 75°

Burbank 90°

San Bernardino 100°

Riverside 96° Santa Ana 84°

Pacific Ocean 68°

San Diego 72°

Palm Springs 106° 70s (°F)

80s 90s 100s

Evaporative Cooling

A water molecule takes energy with it when it evaporates leading to evaporative cooling

Water is a universal solvent

!  Hydration layers around Na+ and Cl– ions keep salt in solution

!  The salt is the solute and the water the solvent

Polar regions on proteins cause solubility in water

Lysozyme molecule in a aqueous environment.!

Solutions: Mix of Solvent and Solute

!  Concentration •  Number of ions or molecules per unit volume

!  Mole •  6.022 X 1023 molecules (Avogadro’s number) •  1 mole of substance = molecular weight in grams •  1 mole NaCl = 23 + 35 = 58g

!  Molarity (moles per liter) •  1 molar solution = 1 mole/liter = 1M •  1M NaCl = 58 g/L

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Water can form Ions

!  Water dissociates to form ions:

H2O ! H+ + OH–

!  H+ (protons) = hydrogen ions !  OH– = hydroxide ions !  In pure water, concentration of H+ = OH–

Acids and Bases contain different amounts of H+ or OH- ions

!  Acids release H+ as they dissolve in water •  Solution becomes acidic

HCl ! H+ + Cl–

!  Bases gather H+ or release OH! in solution •  Solution becomes basic

NaOH ! Na+ + OH–

pH Scale: Measurement of H+ ions

!  pH stands for “potential hydrogen ions” !  Measures relative concentrations of H+ and OH!

(acidity) in a water solution on a scale of 0 to 14

pH = –log10[H+]

!  Pure water: [H+] = [OH!] = 1 X 10-7 M •  pH 7 (neutral) = –log10[1 X 10-7] •  pH < 7 is acidic, pH > 7 is basic

LE 3-8

pH Scale!0!

1!

2!

3!

4!

5!

6!

7!8!9!

10!

11!12!13!14!Oven cleaner!

Household bleach!

Household ammonia!

Milk of magnesia!

Seawater!

Pure water!Human blood!

Urine!Rainwater!Black coffee!Tomato juice!

Vinegar, beer, wine, cola!Digestive (stomach) juice, lemon juice!Battery acid!

Neutral [H+] = [OH–]!

Incr

easi

ngly

Aci

dic

[H+ ]

> [O

H– ]!

Incr

easi

ngly

Bas

ic

[H+ ]

< [O

H– ]!

Acidic: [H+] > [OH-]

Neutral: [H+]=[OH-]

Basic: [H+] < [OH-]

Acid Rain: Rain below pH 5.6

0!1!2!3!4!5!6!7!8!9!

10!11!12!13!14!

More basic!

Normal rain!

More acidic!

Acid rain!

Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acid

Acid Rain destroys biotic and non-biotic environments

The Threat of Acid Precipitation

!  Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6

!  Acid precipitation is caused mainly by the mixing of different pollutants like NO and SO2 with water in the air (nitric acid and sulfurus acid).

!  Acid precipitation can damage life in lakes and streams

!  Effects of acid precipitation on soil chemistry are contributing to the decline of some forests

Ocean Acidification: a threat to water quality

Increasing levels of H+

combine with CO32- and

impair calcification in marine organisms

CO2

CO2 + H2O " H2CO3

H2CO3 " H+ + HCO3#

H+ + CO32# " HCO3

#

CO32# + Ca2+ " CaCO3

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!  Most biological buffers consist of a pair of molecules, one an acid and one a base

Buffers keep pH constant Buffers

!  Regulate pH of living cells

!  Absorb or release H+ to compensate for changes in H+ concentration

H2CO3 ! HCO3– + H+

Van der Waals Forces: weak fleeting charges

d. Pads on a seta a. Gecko inverted on glass b. Gecko toe c. Setae on toe

Van der Waals Forces are weak molecular interactions over short distances

Chemical Reactions

!  When molecules form or break chemical bonds

6 CO2 + 6 H2O " C6H12O6 + 6 O2

carbon dioxide

water a sugar molecular oxygen

reactants products