Properties of Water

Module 2 BIOCHEMISTRY

Properties of Water& pH

The Extraordinary Properties of Water

Water

• A water molecule (H2O), is

made up of three atoms ---
one oxygen and two hydrogen.

Draw

Draw a water molecule. Hydrogen molecules red and the Oxygen molecule blue.

Water is olar

• In each water molecule, the oxygen atom attracts more

than its "fair share" of electrons

• The oxygen end “acts” negative

• The hydrogen end “acts” positive

• Causes the water to be POLAR

• However, Water is neutral (equal number of e- and p+)

--- Zero Net Charge

Water is Polar

Multiple Choice

Water is polar because...

• The unequal sharing of electrons gives the water molecule a slight negative charge near its oxygen atom and a slight positive charge near its hydrogen atoms.

• The molecule has two poles, at which the it is colder than other regions of the molecule.

• The unequal sharing of electrons gives the water molecule a slight negative charge near its hydrogen atoms and a slight positive charge near its oxygen atom.

• The water molecule is neutral.

Hydrogen Bonds Exist Between Water Molecules

★
Electronegative atom of a polar
molecule and a Hydrogen

★

Onehydrogen bond isweak, but
manyhydrogen bonds are strong

Multiple Choice

Attractions between water molecules are called ....

• Covalent bonds

• Ionic bonds

• Polar bonds

• Hydrogen bonds

Multiple Choice

A bond created by the weak attraction of a slightly positive hydrogen atom to a slightly negative portion of another molecule is called ..........

• polar molecule

• solution

• adhesion

• hydrogen bond

Interaction Between Water Molecules

Negative Oxygenend of one water
molecule is attracted to the Positive
Hydrogenend of another water
molecule to form a HYDROGEN BOND

What are the Properties of Water?

● Cohesion
● Adhesion
● High Specific Heat
● High Heat of Vaporization
● Less Dense as a Solid

Cohesion

• Attraction of water between

particles of the same
substance (why water is
attracted to itself)

• Results inSurface tension(a

measure of the strength of
water’s surface)

• Produces a surface film on

water that allows insects to
walk on the surface

Multiple Choice

The attraction that causes water and other liquids to form drops on thin films is called ________________. This is also water’s ability to be attraction to other water molecules.

• adhesion

• capillary action

• cohesion

• surface tension

Multiple Choice

The tendency of molecules of the same kind to stick to one another is called .....

• cohesion

• adhesion

• solution

• polar molecule

Cohesion …

Helps insects walk across

water

Multiple Choice

A water strider can skate along the top of a pond because....

• covalent bonds result in water cohesion (surface tension)

• hydrogen bonds result in water cohesion (surface tension)

• water striders have adapted to become lighter than water

• low surface tension of water

Adhesion Causes Capillary

Action

Which gives water

the ability to “climb”

structures

Adhesion

•Attraction between two different substances.

•Water will makehydrogen bonds with othersurfacessuch as glass, soil, plant
tissues, and cotton.

•Capillaryaction-water molecules will “tow” each other along when in a thin
glass tube.

•Example:transpirationprocess which plants and trees remove water from the
soil, and paper towels soak up water.

Adhesion Also Causes Water to …

Form spheres &
hold onto plant

leaves

Attach to a
silken spider

web

Multiple Choice

What word describes when water is attracted to other substances?

• cohesion

• adhesion

• capillary action

• surface tension

High Specific Heat

• Amount of heatneeded to raise or lower 1g of a

substance 1° C.

• Water resiststemperature change, both for heating

and cooling

• Water can absorb or release large amounts of heat energy

with little change in actual temperature.

Multiple Choice

Water has _____ specific heat. Meaning, it takes a _____ time to warm up a large amount of water.

• high/ long 

• high/ short

• low/long

• low/ short

Multiple Choice

Large bodies of water, such as lakes and oceans, do not quickly fluctuate in temperature. What is the reason for this phenomenon?

• Water is an acid.

• Water is a versatile solvent.

• Water has a high heat capacity.

•  Water acts as a buffer.

High Heat of Vaporization

• Amount of energy to convert 1g or a

substance from a liquid to a gas

• In order for water to evaporate, hydrogen

bonds must be broken.

• As water evaporates, it removes a lot of

heat with it.

• Water vapor forms a kind of global ‘‘blanket” which helps to keep the Earth

warm.

• Heat radiated from the sun warmed surface of the absorbed and held by the

vapor.

Multiple Choice

What property of water allows for water to act as a temperature regulator for the world?

• Cohesive Behavior

• Expansion Upon Freezing

• High Specific Heat

• Universal Solvent

Water is Less Dense as a Solid

• Ice is less dense as a solid than as a

liquid (ice floats)

• Liquid water hashydrogen bonds

that are constantly being broken
and reformed.

• Frozen water forms a

crystal-like latticewhereby
molecules are set at fixed
distances.

Water is Less Dense as a Solid

•
•
•

■ Which is ice and which is water?

Water is Less Dense as a Solid

Water
Ice

Multiple Choice

Why does ice float?

• As water freezes, it expands and its density decreases.

• As water freezes, it takes up more hydrogen from the atmosphere, causing it to have a greater buoyancy.

• As water freezes, air becomes trapped between the hydrogen bonds of water molecules.

• As water freezes, it takes up more oxygen from the atmosphere, causing it to have a greater buoyancy.

Multiple Choice

The fact that ice floats on liquid water is due to the fact that water's solid is ___________ than it's liquid form

• less polar

• more polar

• less dense

• more dense

Homeostasis

• Ability to maintain a steady state despite

changing conditions

• Water is important to this process because:

a. Makes a good insulator
b. Resists temperature change

C.Universal solvent
d. Coolant
e. Ice protects against temperature

extremes (insulatesfrozen lakes)

Solutions & Suspensions

• Water is usually part of a mixture.

• There are two types of mixtures:

Solutions

Suspensions

Solution

• Ionic compounds disperse as ions in water
• Evenly distributed
• SOLUTE

– Substance that is being dissolved

• SOLVENT

– Substance into which the solute dissolves

Solution

Suspensions

• Substances that don’t

dissolve but separate into
tiny pieces.

• Water keeps the pieces

suspended so they don’t
settle out.

Acids, Bases and pH

One water molecule in 550 million

naturally dissociates into a Hydrogen
Ion (H+) and a Hydroxide Ion(OH-)

Hydrogen Ion Hydroxide Ion

Acid Base

H2O ⮀ H+ + OH-

The pH Scale

• Indicates the concentration of H+

ions

• Ranges from 0 – 14
• pH of 7 is neutral
• pH 0 up to 7 is acid … H+
• pH above 7 – 14 is basic… OH-

Multiple Choice

In an acidic solution

• The hydroxide ion concentration is greater.

• The hydrogen ion concentration is greater.

• The are equal amounts of hydrogen and hydroxide ions.

Multiple Choice

In an basic solution

• The hydroxide ion concentration is greater.

• The hydrogen ion concentration is greater.

• The are equal amounts of hydrogen and hydroxide ions.

Multiple Select

What does pH measure?

• Concentration of H⁺

• Concentration of OH^-

• The amount of liquid in the test tube.

• The Concentration of H₃O⁺

Multiple Choice

An acid’s pH is between :

• 0 to 6

• 7

• 8-14

• 6-14

Multiple Choice

The pH scale is a range from:

• 1-7

• 0-14

• 1-5

• 1-20

Acids

• StrongAcids have

a pH of 1-3

• Produce lots of

H+ ions

•WeakAcids
a pH of 5-7

Multiple Choice

A substance with a pH of 7 is

• acidic

• basic

• neutral

Multiple Choice

Which of the following is the strongest acid?

• 1

• 5

• 3

• 8

Multiple Choice

Which of the following is a characteristic of an acid?

• bitter

• slippery

• sour

• releases hydroxide ions in water

Bases

StrongBasis
a pH of 11-14

Produce lots
of OH- ions

WeakBasis
a pH of 7-9

Multiple Choice

A substance with a pH of 4 is

• acidic

• basic

• neutral

Multiple Choice

Which of the following is the strongest base?

• 4

• 14

• 7

• 15

Buffers

• Weak acids or bases that react with strong

acids or bases to prevent sharp, sudden
changes in pH (neutralization).

• Produced naturally by the body to maintain

homeostasis

Weak Acid

Weak Base