2.2 Properties of Water – Guided Notes
The Water Molecule
Water is one of the few compounds found in a ________________________ over most of
Earth’s surface.
Like other molecules, water (H2O) is _______________. The positive charges on its ____
_________________ balance out the negative charges on its ____electrons.
Polarity
Because of the angles of its chemical bonds, the ___________________ atom is on one end
of the molecule and the ______________________ atoms are on the other.
With 8 protons in its _______________, an oxygen atom has a much stronger attraction for
electrons than does a hydrogen atom with its ___________________ proton.
Polarity
There is a greater probability of finding the shared electrons in water close to its oxygen
atom than near its ________________________ atoms.
As a result, the oxygen end of the molecule has a slight ___________________ charge and
the hydrogen end of the molecule has a slight ____________________ charge.
Polarity
A molecule in which the charges are unevenly distributed is said to be “_______________,”
because the molecule is a bit like a ____________________ with two poles.
The charges on a polar molecule are written in parentheses, (–) or (+), to show that they are
+
–
weaker than the charges on _____________ such as Na and Cl .
Hydrogen Bonding
Because of their ________________________________________________________,
polar molecules such as water can attract each other.
The attraction between a hydrogen atom on one water molecule and the oxygen atom on
another is known as a _______________________________.
Hydrogen Bonding
Water is able to form ____________________________________________, which account
for many of its special properties.
Hydrogen bonds are _________________________________ as covalent or ionic bonds,
and they can form in other compounds besides water.
Cohesion
_____________________________________ is an attraction between molecules of the
same substance.
Because a single water molecule may be involved in as many as four hydrogen bonds at the
same time, ______________________________________________________.
Cohesion
Cohesion causes water molecules to be _____________________________________,
which is why drops of water form beads on a smooth surface.
Cohesion also produces ______________________________, explaining why some insects
and spiders can walk on a pond’s surface.
Adhesion
_____________________________is an attraction between molecules of
_______________________substances.
The surface of water in a graduated cylinder dips slightly in the center, forming a curve
called a __________________________________, because the adhesion between water
molecules and glass molecules is stronger than the cohesion between water molecules.
Adhesion
Adhesion between ___________________________________ also causes water to rise in a
narrow tube against the force of gravity. This effect is called _________________________.
Capillary action is one of the forces that draws water out of the roots of a plant and up into
its stems and leaves.
______________________________ holds the column of water together as it rises.
Heat Capacity
Because of the multiple hydrogen bonds between water molecules, it takes a
_____________________________________________________ to cause those molecules
to move faster and raise the temperature of the water.
Water’s heat capacity, _______________________________________________________
______________________________________, is relatively high.
Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only
small changes in temperature. This protects organisms living within from drastic changes in
temperature.
At the cellular level, water absorbs ______________________________________________
________________________________________________________________.
Solutions and Suspensions
How does water’s polarity influence its properties as a _______________________?
Solutions and Suspensions
Water’s polarity gives it the ability to dissolve _____________________________
compounds and other _____________________ molecules.
Solutions and Suspensions
Water is not always pure; it is often found as part of a _______________________.
A ____________________ is a material composed of two or more elements or compounds
that are _______________________________ mixed together but not chemically combined.
Living things are in part composed of mixtures involving water.
Two types of mixtures that can be made with water are ___________________ and
____________________________.
Solutions
If a crystal of table salt is placed in water, sodium and chloride ions on the surface of the
crystal are attracted to the polar water molecules.
Solutions
Ions break away from the _________________ and are ________________________ by
water molecules.
The ions gradually become dispersed in the water, forming a type of mixture called a
__________________________.
Solutions
All the components of a solution are _____________________ distributed throughout the
solution.
In a saltwater solution, table salt is the _________________—the substance that is
dissolved.
Water is the ________________________—the substance in which the solute dissolves.
Solutions
Water’s polarity gives it the ability to dissolve both ionic compounds and other polar
molecules.
Water easily dissolves _______________________________________________________
_________________________________________________________________________.
When a given amount of water has dissolved all of the solute it can, the solution is said to be
____________________.
Suspensions
Some materials do not dissolve when placed in water, but separate into pieces so small that
they do not settle out. ________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
Some of the most important biological fluids are both solutions and suspensions.
_______________ is mostly water. It contains many dissolved compounds, but also cells
and other undissolved particles that remain in suspension as the blood moves through the
body.
Acids, Bases, and pH
Why is it important for cells to buffer solutions against rapid changes
in pH?
Acids, Bases, and pH
Buffers dissolved in life’s fluids play an important role in maintaining _________________
in organisms.
Acids, Bases, and pH
Water molecules sometimes split apart to form ____________________________________
_________________________________________________________________________.
This reaction can be summarized by a chemical equation in which double arrows are used to
show that the reaction can occur in either direction.
Acids, Bases, and pH
In pure water, about 1 water molecule in 550 million splits to form ions in this way.
Because the number of ___________________ hydrogen ions produced is equal to the
number of _____________________ hydroxide ions produced, pure water is
________________________.
The pH Scale
Chemists devised a measurement system called the _______________________ to indicate
+
the concentration of H ions in solution.
The pH scale ranges from ____________________.
+
–
At a pH of 7, the concentration of H ions and OH ions is equal. Pure water has a pH of 7.
The pH Scale
Solutions with a pH below 7 are called ___________________ because they have more
+
–
H ions than OH ions. The lower ______________________________________________.
–
+
Solutions with a pH above 7 are called basic because they have more OH ions than H ions.
The ______________________________________________________________________.
The pH Scale
Each step on the pH scale represents a factor of _________. For example, a liter of a
+
solution with a pH of 4 has 10 times as many H ions as a liter of a solution with a pH of 5.
Acids
+
An __________________ is any compound that forms H ions in ____________________.
+
Acidic solutions contain _________________ concentrations of H ions than pure water and
have pH values below 7. Strong acids tend to have pH values that range from 1 to 3.
_________________________________ acid (HCl) is a strong acid produced by the
stomach to help digest food.
Bases
–
A ___________ is a compound that produces __________________ (OH ) ions in solution.
+
Basic, or _______________, solutions contain lower concentrations of H ions than pure
water and have pH values above 7. Strong bases, such as the lye (commonly NaOH) used in
________________________________, tend to have pH values ranging from 11 to 14.
Buffers
The pH of the fluids within most cells in the human body must generally be kept between
6.5 and 7.5 in order to maintain ____________________________. If the pH is lower or
higher, it will affect the chemical reactions that take place within the cells.
One of the ways that organisms control pH is through dissolved compounds called
_____________________, which are weak acids or bases that can react with strong acids or
bases to prevent sharp, sudden changes in pH.
Buffers
___________________________________________ causes the pH of the unbuffered
solution to ________________. If the solution contains a buffer, however, adding the acid
will cause only a slight change in pH.