Properties of Water
Nov 18, 2014
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