A Question to Ponder

Why do living things require water?

Watch the video

​https://youtu.be/CMtAUdJcLA4

� Polar covalent – electrons are shared

unequally

� Oxygen atom holds e- more than Hydrogen as

a result O has a partial negative charge

� Hydrogen atoms holds e- less than Oxygen

as a result, the hydrogen atoms have a partial
positive charge

Meet Water

� Polar covalent – electrons are shared

unequally

� Oxygen atom holds e- more than Hydrogenas

a result O has a partial negative charge

� Hydrogen atoms holds e- less than Oxygen

as a result, the hydrogen atoms have a partial
positive charge.

This makes the hydrogen side have a + charge and the Oxygen side a negative charge.

Meet Water

� Has unique properties that make it critical to

life

- result from the fact that water is a polar

molecule that forms hydrogen bonds between
its molecules.

Water has hydrogen bonds

A solution is a mixture of one or more solutes

dissolved in a solvent.

WHAT IS A SOLUTION?

� In order for chemical reactions to happen in

living things, they must be in solution
-Solvent - fluid that dissolves solutes

-Solute – the solute is dissolved in the
solvent

Water is the Solvent of Life

� The charges on a water
molecule interact with
charges on solutes

- allows water to dissolve the
substance

- water molecules are attracted
to the charges on the
substance and pull it apart either into smaller pieces or ions.

Water as solvent

POLAR Molecule is when a molecule is positive on
one end and negative on the other.

Ex. Water

Polar and Nonpolar

Which Color is the Hydrogens?

Which Color is the Oxygens?

Which side is Negative? Oxygen or
Hydrogen side?

Polar and Nonpolar

Nonpolar Molecule is when a molecule has its
charges balanced out, so there is not one end that
is negative and one end that is positive

Ex. Methane

It can determine solubility, or the ability of a solute
to dissolve in a solvent.

Why is knowing polar and nonpolar important?

� Hydrophilic (water loving) substances – have

charges and dissolve in water, are either polar
covalent substances or ionic substances
○ Like dissolve like
○ Water is a polar molecule and dissolves

other polar molecules

� Hydrophobic (water hating) substances – lack

charges and don’t dissolve in water are
nonpolar covalent substances

Water as a solvent

HYDRO MEANS?

� Cohesion – the attraction between water
molecules
- creates surface tension

Cohesion and Adhesion

Adhesion – the attraction between water

molecules and other substances

​https://youtu.be/A8n678m6ZqI

� Cohesive and adhesive forces together, allow

water to climb

� Helps explain why water can reach the top of
large trees.

Capillary Action

Water has a high specific
heat

� Specific Heat – the amount of energy needed to

raise 1g of a substance 1 degree C

○ Water take more energy than some things in

order to get hot

� This means that water can absorb a lot of heat

before it begins to get hot. This is why water is
valuable to industries and in your car's radiator
as a coolant.

� The hydrogen bonds in ice lock the molecules in

place.

- creates more space between the

molecules = less dense

Why is this important? Ice floats – allows life to

continue in water even in winter

Water is Less Dense as a Solid

� Water can break into ions

H2O H+ + OH-

Water Hydrogen Hydroxide

ion ion

Acids and Bases

pH Scale - describes the
concentration of H+ ions in a
solution → How acidic/How
basic something is

Acids range from 6.9 – 0
(BELOW 7)

Bases range from 7.1 – 14
(ABOVE 7)

7 is neutral: = H+ and OH- ions

Why is pH Important to Life?

� Living things must keep their pH within a narrow range.

◦ Human blood must be kept near pH 7.4 or we die

◦ Once pH gets outside of a narrow range, it interferes

with the chemical reactions necessary for life

Water is a main component of the human body, including
blood, which is why our blood is close in pH to water pH.

Does the temperature
of the solvent matter?

Question

Concentration

• the amount of solute dissolved in a solvent

at a given temperature

Concentration

•described as unsaturated if it has
a low concentration of
solute

•described as saturated if it
has a high concentration of
solute

•described as supersaturated if
contains more dissolved solute
than normally possible

Which one is the
solute?
Solvent?

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