WaterWater

Why is water so important to Why is water so important to life?life?

Water covers more than 75% of the Earth’s surface.Water covers more than 75% of the Earth’s surface.

Living organisms are composed of 60-90% water.Living organisms are composed of 60-90% water.

Life is dependent on water.Life is dependent on water.

Oxygen (-)

Hydrogen(+)

Hydrogen(+)

Let’s Let’s ReviewReview

Water Has Unique PropertiesWater Has Unique Properties

Cohesion makes it a group effortCohesion makes it a group effort

Adhesion makes it a sticky situationAdhesion makes it a sticky situation

Surface tension makes it hardSurface tension makes it hard

Water helps makes the Earth bearableWater helps makes the Earth bearable

High specific heat- it’s a heat sinkHigh specific heat- it’s a heat sink

High heat of vaporizationHigh heat of vaporization

High heat of fusionHigh heat of fusion

Water is the universal solventWater is the universal solvent

Hydrophilic moleculesHydrophilic molecules are attracted to are attracted to water and can be dissolved by water.water and can be dissolved by water.

Ex. Proteins, salts, and sugarsEx. Proteins, salts, and sugars

Ex. SaltwaterEx. Saltwater

Hydrophobic moleculesHydrophobic molecules repel water and repel water and therefore cannot be dissolved by water.therefore cannot be dissolved by water. Ex. OilEx. Oil

Ionization of Water - Ionization of Water - water breaks water breaks apart into hydrogen and hydroxide ionsapart into hydrogen and hydroxide ions

Pure water breaks apart into equal numbers of Pure water breaks apart into equal numbers of these ionsthese ions

Some substances do not release equal Some substances do not release equal numbers of Hnumbers of H + + and OHand OH--..

What are they? What are they? Acids Acids andand BasesBases

Acids are substances that release H ions Acids are substances that release H ions into solution when they disassociate into solution when they disassociate

Ex. HCl HEx. HCl H++ + Cl + Cl--

Acids taste sour Acids taste sour

Ex. Vinegar or Lemon juice Ex. Vinegar or Lemon juice

Bases are substances that accept H ions Bases are substances that accept H ions

Ex. NaOHEx. NaOH Na Na++ + OH + OH--

Two examples of how bases do this Two examples of how bases do this

Ex. NHEx. NH33 + H + H++ NH NH44

Bases are slippery Bases are slippery

Ex. Bleach or SoapEx. Bleach or Soap

How can we determine the acidity of a solution? How can we determine the acidity of a solution?

pH ScalepH Scale

pH measures pH measures the the concentration concentration of H ions of a of H ions of a substancesubstance

So, why is pure water neutral?So, why is pure water neutral?

It ionizes into equal parts of H and OH It ionizes into equal parts of H and OH ions ions

Why is pH important to life?Why is pH important to life?

Organisms must maintain the pH of their Organisms must maintain the pH of their bodies within a normal range bodies within a normal range (homeostasis)(homeostasis)

Ex. blood pH or stomach pHEx. blood pH or stomach pH

How could organisms prevent pH How could organisms prevent pH from fluctuating dramatically?from fluctuating dramatically?

Buffers Buffers are chemicals that minimize the are chemicals that minimize the fluctuation of pH by either accepting H ions or fluctuation of pH by either accepting H ions or releasing them. releasing them.

Ex. Carbonic Acid (weak acid, pH = 6.4)Ex. Carbonic Acid (weak acid, pH = 6.4)

Serves as a buffer for our bloodServes as a buffer for our blood