The Science of Water in the Living World

Water is a polar molecule.•Polar Molecule: a molecule that has a slightly positive side and a slightly negative end.

– The are more electrons surrounding the oxygen atom than the hydrogen atoms.

– Oxygen atom has a slightly negative charge.

– Hydrogen atoms has a slightly positive charge.

Polarity and Hydrogen Bonding

• Hydrogen Bonds: A weak bond that forms between the positive end of one water molecule and the negative end of another water molecule.

• How is a hydrogen bond different than a covalent bond?

Properties of Water•Adhesion: a water molecule forms a hydrogen bond to a surface or an object.

Polarity and Hydrogen Bonding

– Cohesion makes water have high surface tension – it is difficult to break the surface of a body of water.

– Cohesion makes water a viscous liquid – it is difficult to move through.

Properties of Water•Cohesion: a water molecule forms a hydrogen bond with another water molecule.

Polarity and Hydrogen Bonding

Capillary Action: waters ability to flow in narrow spaces against the force of gravity because of adhesion and cohesion.Examples:•Water flowing into the spores of a sponge•Water flowing into plant roots and up the plant stem.•Groundwater moving up through soil.

Polarity and Hydrogen Bonding

Water can mix other polar/ionic molecules.• Polar molecules can be referred to as hydrophilic (water

loving)• Solute – the substance being dissolved• Solvent – the substance in which the solute is dissolved.• Ex: Salt (solute) dissolves in water (solvent).

Polarity and Hydrogen Bonding

• Salt crystals dissolve in water– The negative end of the water molecules are attracted

to the positive ions in salt.– The positive end of the water molecules are attracted to

the negative ions in salt.– Water molecule surround each ion and keep them

separated.

Polarity and Hydrogen Bonding

• Water does not mix with nonpolar molecules.– Non polar molecules can be referred to as

hydrophobic (water fearing).– Water (polar) and oil (nonpolar) do not mix.

Chemical Properties of Water

Water molecules are in constant motion. The higher the temperature the faster the molecules are moving.

The Three States of Water:•Gas (vapor): When a water molecule moves fast enough it breaks free of all hydrogen bonds and becomes a gas.

– Water molecules are spread much further apart than in liquid water.

– Increasing temperature, increases the rate of evaporation.

Heat and Water

The Three States of Water:•Liquid: Hydrogen bonds hold most of the water molecules together in small groups.

– Hydrogen bonds are constantly being broken and reformed.

– Cold Water: Is more dense because molecules move slower and packed in tighter causing.

– Warm Water: Is less dense because molecules move faster and spread out.

Heat and Water

The Three States of Water:•Ice: when water freezes, the molecules move so slowly that hydrogen bonding locks each molecule in place forming a crystal.

– In ice, the water molecules are further apart than in liquid water.

– Ice is less dense than liquid water.

– Why is it important that ice floats in the ocean?

Heat and Water

Heat Capacity: The amount of heat needed to raise the temperature of a substance.•Water has the highest heat capacity of any natural substance. • Heat energy must

be used to break hydrogen bonds between water molecules before the molecules are able to move faster and increase temperature.

Heat and Water

• A relatively constant water temperature helps organisms maintain homeostasis: an organism’s ability to maintain constant and stable internal conditions.

• It takes a long time and a lot of energy for water to heat up or cool down.

• Water’s high heat capacity protects organisms from drastic changes in temperature.

Heat and Water

Acid, Bases and pH• Water molecules sometimes split apart to from ions.• What is an ion?

• Pure water is neutral it has a equal number of positive and negative ions

The pH of Ocean WaterAcids and Bases

Acids• Have more H+ ions

than OH- ions in solution.

• pH less than 7• The lower the

number, the stronger the acid.

• Ex: HCl is a strong acid produced by the stomach to digest food.

Bases

• Produces more OH- ions than H+ in solution

• pH greater than 7

• The higher the number the stronger the base.

• Ex: NaOH is a basic (alkaline) solution used in soap making.

Acids and Bases

pH: (power of Hydrogen) as in Hydrogen ions• Measures the H+ concentration in solution: [H+]• It is a log scale, so it increases by powers of ten.• Ex: pH 2 = [H+] of 0.01M, pH 3 = [H+] of 0.001M• Ex: A solution with a pH of 2 is ten times more acidic then

a solution with a pH of 3.

Acids and Bases

Buffer: A solution that prevents sharp and sudden changes in pH.

• Many land animals have buffers in their blood that maintain a constant pH.

• Ocean water acts as a buffer and resists changes in pH.

• If the pH of an organism changes, it will affect the chemical reactions inside their cells.

• Buffers help organisms maintain homeostasis with respect to pH.

Acids and Bases

1. According to the scale, what substance is neutral?

2. What solution has an [H+] of 0.0001M?

3. Which substance produce the most OH- ions in solution?

4. How many more times basic is tomato juice compared to pure water.

Acids and Bases