2)
Objectives
1) Explain why water molecules are polar.
What is the difference between solutions and suspensions.
3) Explain what acidic solutions and basic solutions are.
Warm Up
 Balloon and fire
Introduction
 Water
 The single most abundant
compound in most living
things
 One of the few
compounds that is a liquid
at the temperatures found
over much of Earth’s
surface
 Expands as it freezes
 Ice is less dense than
liquid water
Water Molecule
 Neutral
 10 Protons
 10 Electrons
Polarity
 Oxygen atom has a much
stronger attraction for
electrons
 Greater probability of
finding the shared
electrons near oxygen
atom
 Oxygen side of a water
molecule has a slight
negative charge
 Polar molecule: a
molecule in which the
charges are unevenly
distributed
Polarity Cont’d
 A water molecule is polar
because there is an
uneven distribution of
electrons between the
oxygen and hydrogen
atoms
 Bending Water Demo
Hydrogen Bonds
 Polar molecules can
attract each other
 Hydrogen bonds are not
as strong as covalent or
ionic bonds
 Water can form many
hydrogen bonds
 Responsible for water’s
many special properties
Hydrogen Bonds Cont’d
 Cohesion: an attraction between molecules of the same
substance
 Water is extremely cohesive
 Causes molecules on the surface of water to be drawn inward
 https://www.youtube.com/watch?v=45yabrnryXk
Hydrogen Bonds Cont’d
 Adhesion: an attraction
between molecules of
different substances
 Capillary action: causes
water to rise in a narrow
tube against the force of
gravity

One of the forces that
draw water out of the roots
of a plant and up into its
stems and leaves
Solutions and Suspensions
 Mixture: a material
composed of 2 or more
elements or compounds
that are physically mixed
together but not
chemically combined
 2 types
 Solutions
 Suspensions
Solutions
 Solution: the ions gradually
become dispersed in the
water
 Evenly distributed
 Solute: the substance that is
dissolved
 Solvent: the substance in
which the solute dissolves
 Water’s polarity gives it the
ability to dissolve both ionic
compounds and other polar
molecules
 The greatest solvent on Earth
Suspensions
 Suspensions: mixtures
of water and
nondissolved material
 Some materials do not
dissolve in water
 Separate into pieces that
do not settle out
The pH Scale
 pH scale: a measurement system to show the concentration of positive
hydrogen ions in a solution
 Scale of 0-14
 0-3 is acidic
 More H+ ions
 4-10 is neutral
 11-14 is basic
 More OH- ions
Acids
 Acid: any compound that forms H+ ions in solution
 Acidic solutions have higher concentrations of H+ ions than pure water and
have pH values below 7
 Strong acids range from 1-3
 https://www.youtube.com/watch?v=8ANWDrRd-IQ
Bases
 Base: a compound that produces OH- ions in a solution
 Basic (alkaline) solutions have lower concentrations of H+
ions than pure water
 pH values are 11-14
 https://www.youtube.com/watch?v=yL1Kyeke-Kg
Buffers
 pH of the fluids w/I most cells in the human body
must generally be kept between 6.5-7.5
 Different pH will affect chemical reactions in cells
 Controlling pH is important for maintaining
homeostasis
Buffers Cont’d
 Buffers: weak acids or
bases that can react with
strong acids or bases to
prevent sharp, sudden
changes in pH
2-2 Exit Ticket
 Answer the following
1) Explain why water
questions.
 Use complete sentences.
 You may NOT use your
book. You MAY use your
notes.
 This is a quiz grade.
molecules are polar.
2) What is the difference
between solutions and
suspensions.
3) Explain what acidic
solutions and basic
solutions are.