Properties of Water

Polarity• Caused by the unequal sharing of electrons

• Electrons spend more time near the oxygen atom because it contains more protons.

• The unequal sharing creates poles within the molecule

PolarityOxygen

Proton

Neutron

Electron

Hydrogen

Negative

Positive

Bond

Hydrogen Bonds• Created through the attraction of positive

and negative poles of polar molecules.

• Similar to Van der Waals force

• Not as strong as covalent or ionic bonds but stronger than a Van der Waals force

-

++ -

-

+

Types of H-bonds• Cohesion

– an attraction between molecules of the same substance.

– Creates surface tension in water

• Adhesion– an attraction between molecules of two

different substancesCohesion

Mixtures• Definition - material composed of 2 or more

elements that are physically mixed but not chemically combined

• Two types involving water– Suspensions – Solutions

Suspensions• A mixture involving water where the

particles are not dissolved but do not settle at the bottom either

Solutions• A mixture involving water where all of the

components are evenly distributed

• Solute- Substance that is dissolved

• Solvent - the substance in which the solute is dissolved. Water is the most common solvent in the world

Solutions

The pH scale • Used to measure the amount of hydrogen

ions (H+) present in solution

• Each step on the scale is a factor of 10, 14 having the least and 1 having the most H+ ions.

• Pure water has a pH of 7 (neutral)

1 4 7 10 14

Question!

• How many more H+ ions would a solution with a pH of 3 have when compared to that with a pH of 5?

• The pH of 3 would have 100 times more H+ ions than the the solution with a pH of 5.

Acids

• any compound that releases H+ ions into solution

• Acidic solutions are those with a pH below 7

Strong AcidStomach Acid

Weak AcidVinegar

Neutralwater

Bases

• Any compound that releases hydroxide ions (OH-) into solutions

• Basic, or alkaline, solutions have a pH greater than 7

• Bases have the ability to absorb H+ ions in solution

NeutralWater

Weak BaseSoap

Strong BaseBaking Soda

Question!

• If a base absorbs H+ ions in solution, what does an acid absorb?

• An acid has the ability to absorb OH- ions

Buffers

• weak acids or bases that aid in controlling pH.

• Buffers prevent sudden pH changes

• Buffers allow organisms to maintain homeostasis