Properties of Water
When a compound is made, normally that
compound is neutral because all of the (+)
charges have a matching (-) charge.
In a water molecule,
Oxygen:
Hydrogen:
Hydrogen:
8 Protons
1 Proton
1 Proton
Oxygen: 8 electrons
Hydrogen: 1 electron
Hydrogen: 1 electron
However, they don’t exactly share them
evenly. In fact the Oxygen wants the
electrons so much, it kind of “hogs” them from
the Hydrogen.
This is because of the large amount of (+)
charge from the oxygen
Because the Oxygen “hogs” the hydrogen
electrons, it has a slight negative charge on
the oxygen end. (Electrons are negative charged)
This leaves the Hydrogen atoms (with less electron
power) with a slight positive charge.
This results in what we call a “Polar molecule”
Just like a magnet that has a (+) and a (-) end,
The water molecule has a (+) and a (-) end
because the oxygen is hogging the electrons.
So that means when water molecules form
together. They work like magnets. (+)(-)
attract each other.
The bonds between the water molecules are
called HYDROGEN BONDS. (chemical attractions
of polar molecules)
http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html
These hydrogen bonds are weak bonds, not as
strong as Ionic or covalent
Every 1 water molecule can join
with 4 others.
Cohesion – an attraction between
molecules of the same substance
So water is a very “Cohesive” molecule.
Adhesion – attraction between molecules of
different substances.
Glass is a polar molecule which
attracts the water molecules.
This is why some water stays
along the edge of a glass when
you pour slowly. You give the
water & glass time to form
adhesion.
Trying to fit as many water drops on a penny
shows you both the “cohesive” and “adhesive”
properties of water.
MIXTURES &
SOLUTIONS
A Mixture is a material composed of 2 or more
elements that are physically mixed together,
but not chemically combined.
A salt & pepper
mixture.
Chocolate chips
& cookie dough
A solution is a mixture that has the same
composition, color, density, and sometimes
even taste throughout.
Try adding blue food coloring to a jar, what
happens over time is that the coloring evenly
mixes all throughout the jar.
It has become a completely
homogenous mixture where
the molecules of coloring
have mixed evenly among
the water molecules.
To describe a solution you normally say that
one substance is dissolved into another.
(like sugar into tea)
The substance being dissolved (the sugar) is
called the solute.
The substance that is doing the dissolving
(tea) is called a solvent.
Everyone should know what the
greatest solvent in the world is.
Suspensions – are mixtures of water and nondissolved material.
Blood is a mixture of water,
red blood cells, white blood
cells, plasma, and platelets.
Yet, is forms a liquid
mixture because all the
things above do not react
with each other.
Hydrophilic
molecules are
water loving and
have an affinity
for water.
Hydrophobic
molecules will
repel water
Acid / Base
A molecule of water occasionally break into 2
parts.
H2O
H+ +
Hydrogen
ion
OHHydroxide
ion
This only occurs about once per 550 million
molecules of water.
Water as a whole still remains neutral charges
because it even the (+) charged H+ and the (-)
charged OH- cancel each other out.
Chemists devise a pH scale to determine how
many H+ ions are in a solution.
0
7
14
The scale runs from 0 to 14, with 7 being the
middle or “neutral”
This means at pH 7, the number of H+ ions is
equal to the number of OH- ions.
Most of you should already know the pH scale
Low pH numbers 1-6 are called Acids,
7 is neutral,
High pH numbers 8-14 are Bases
The lower the number, the more “acidic” or
the higher the H+ amount is.
Getting more Alkaline
Getting more acidic
0
7
The higher the number, the more “basic” or
“alkaline” the higher the OH- amount is.
14
Each number on the pH scale is a factor of 10. so for
every number you move in a direction, each number
means (x10)
If someone added an acid to your pure water… enough
to lower it 1pH, how much more H+ ion do you have?
2
3
4
5
6
0
8 9
10 11
14
7
100,0010,0001000X100X
0X
X more more
more more
H+ H+
H+
H+ ions ions
ions ions
10X
more
H+
ions
10X 100X1000X10,000
more more more X
more
OH- OH- OHions ions ions OHions
Problem: Bill had a solution at pH6, adding
another chemical to it dropped the pH to pH 3.
How many more H+ ions does this new solution
have?
0
3
6
7
1000 times more H+ ions
Is it more acidic or basic than the original
solution?
14
Litmus paper is another indicator of pH.
There is a red and blue litmus paper, but what
is important is what color the paper turns
when dipped into the solution.
Blue means Base
acid turns RED
So the
solution to
the right is?
Many times you need to know
how strong or weak the acid
or base is, so on those
occasions you can use pH
paper like the one to the
right.
The paper will turn a different color depending
on the amount of H+ ions.
PROPERTIES OF ACIDS
Acids have several common properties:
1. Acids taste sour.
- The familiar sour taste in some foods is due
to acid. - Still, you should not taste every acid because
some acid can cause severe tissue burning.
2. Some Acids are corrosive.
- They seem to eat away the metal. Metallic
compounds and hydrogen ions form.
3. Acids react with indicators
When an acid reacts with an indicator, you will
see a noticeable color change.
This process is called
Titration.
FOOD ACIDS
Some of the more common acids you see in
foods are:
Citric Acid
Lactic Acid
Acetic Acid
A very strong hydrochloric acid is found in
your stomach which helps dissolve or break
down your foods.
BASES
You might not be as familiar with bases, but
there are some involved in your daily lives…
Egg whites
Baking
Powder
Soap
Antacids
Ammonia
PROPERTIES OF BASES
1. In the pure, undissolved
state, many bases are
crystalline in form. (crystals)
2. Bases feel slippery
3. Bases have a bitter taste.
Bitter coffee
4. Bases are corrosive just like acids. (Lye)
5. Bases also react with
indicators.
Using Red litmus paper in a
base, turns the paper blue
Blue means
Base
So drinking a lot of Grapefruit juice, since it
has a lot of acid in it, will lower my body’s pH
level right?
Not really, because inside your body you have
dissolved compounds called “Buffers” that
maintain your normal body pH around 6.5 to 7.5
This is another way the body maintains
“Homeostasis” – a stable internal environment.
Specific Heat
Amount of heat that must be absorbed or lost for
1 g to change 1 degree Celsius.
1 gram of water changing 1 degree C = a
calorie
Specific heat of ethyl alcohol = . 6 cal/g/C
VOCABULARY!
Polar Molecule
Hydrogen Bonds
Cohesion
Adhesion
Mixture
Solution
Solute
Solvent
Suspension
pH scale
Acid
Base
Alkaline
Buffer