DP BIO Y1 - A1.1 Water

Why is water a polar molecule?

-oxygen is more electronegative than hydrogen

-electrons are shared UNEQUALLY

-oxygen becomes partly negative, hydrogen atoms become partly positive

Polar Molecule

uneven sharing of elections (partial negative, partial positive side)

Nonpolar molecules

share electrons equally (balanced charge)

What is a Hydrogen Bond?

A weak attraction between a slightly positive hydrogen atom in one polar molecule and a slightly negative atom in another molecule

Cohesion

the attraction between molecules of the same substance. (water & water)

Adhesion

The attraction between different substances (water & another substance)

Surface Tension

A physical property of liquids that makes the surface layer behave like a stretched elastic sheet.

-cohesion between water is greater than the attractions between water and the floating objects

Example: water striders, overfilled glass

Why does water have high surface tension?

Because its molecules stick together very strongly (because water molecules form tight Hydrogen bonds with one another, called cohesion)

Why is water an excellent solvent?

because water is polar, it can surround and separate ions and other polar molecules

Hydrophilic

water-loving

-substances that interact readily with water

-polar

-charged

hydrophobic

Substances that do not interact readily with water

-nonpolar

-many lipids/hydrocarbons

Specific Heat Capacity

The amount of energy required to raise the temperature of a substance by 1°C per unit mass.

-water → helps buffer the temperature (ex: beaches have more regulated temperatures)

Why does water have a high specific heat capacity?

A lot of energy is required to disrupt the hydrogen bonds between water molecules before their kinetic energy—and therefore temperature—can increase substantially.

-water can absorb lots of heat with relatively little temperature change (helps organisms maintain stable internal temperatures, aquatic environment→ seal)

What is heat of vaporization?

Water requires a relatively large amount of energy to vaporize because hydrogen bonds must be broken.

-evaporative cooling (when water evaporates from a surface, the highest energy molecules leave, which removes heat)

ex: sweating → evaporation of water → heat removed → cooling

Hydrolysis

Water is used to break bonds in larger molecules.

ex: large molecule + water → smaller molecules

Condensation/dehydration reactions

Water is produced when small molecules join together

ex: smaller molecules → larger molecule + water

Xylem

water moves through the xylem

hydrogen bonding contributes to:

-cohesion between water molecules allows the transport of water under tension in plants

-adhesion between water and xylem walls

-together these contribute to the movement of water through the narrow xylem tubes

Each water molecule can form hydrogen bonds with up to — other water molecules

4

Catabolic reaction

breaks down larger molecules into smaller molecules

Anabolic reaction

Builds larger molecules from smaller molecules

Physical Properties of water

Buoyancy

Viscosity

Thermal Conductivity

Specific Heat Capacity

Buoyancy

an upward force applied to an object immersed in a fluid

if the buoyant force of a fluid > object weight = object will float

Viscosity

Measure of a fluid’s resistance to flow

thick fluid → high viscosity

thin fluid → low viscosity

Thermal Conductivity

how easily energy transfers through a material

LESS CONDUCTIVE: heat moves slowly thru the material, better for insulation and preventing heat loss (styrofoam, air, wool)

MORE CONDUCTIVE: heat rapidly moves through the material, better for absorbing and transferring heat (water, copper)

Specific Heat Capacity

the quantity of heat needed to raise the temperature of a chemical per unit mass

-water has the highest specific heat capacity of any liquid. it takes a lot longer to raise air temperature compared to water

Ringed Seal (example of water properties)

buoyancy → allows it to stay afloat without expending much energy

thermal conductivity → blubber

specific heat capacity → temperature of water is steady

viscous water → seal can streamline through as it swims to make it easier (adaptation)

Black throated loon

buoyancy (water) → bird can stay afloat without expending energy

air → not viscous → loon can easily fly

air → low specific heat capacity → fluctuating temperature

air → low thermal conductivity → loon doesnt lose much body heat

Goldilocks Zone

The region around a star where it is neither too hot nor too cold for liquid water to exist on a planet's surface (Earth is at the perfect position!)

Capiliary Action

Draws water up narrow tubes and porous solids like paper (can be caused by adjesion)

Solvent

substance that dissolves (water)

Solute

Substance being dissolved

Solution

Solvent + Solute