1. Republic of the Philippines
Region I
Division of Pangasinan II
MANAOAG NATIONAL HIGH SCHOOL
Manaoag,Pangasinan
CHEMISTRY
Unit VI :
Solutions at Work
Submitted by
III-Rizal(2013-2014):
Rina B. Ramos
Billy Joe C. Baradi
Jefferson T. Soriano
Submitted to :
Mrs. Lourdes Mejia
Science III Teacher

2. Lesson A: Using the Electrolyte
Certain solids can conduct electricity because of the free flow of electrons
in their structure. Electric current consists of electrons freely moving in a metal
conductor under an applied electric potential. The metal conductor is called an
electrical conductor . Solutions may or may not conduct electricity . Solutions that
conduct electricity are called electrolytes. Solutions that do not have electrical
conducting property are non-electrolytes.
The migration of ions in a solution constitutes an electric current. The solution
called an electrolytic conductor. An electrolyte solution is one containing ions.
Solutions of salt, acid, and base are very good electrolytes.
A strong sound indicates many ions are present in a solution. The weak sound
indicates only a small amount of ions are present in a solution.
The active component of vinegar is acetic acid ( CH3COOH),an organic acid.
Unlike HCl, acetic acid is only partially dissociated in solution. We may represent its
dissociation by:
_
+
CH3COOH
CH3COO + H
acetic acid
acetate ion
hydrogen ion
The double arrows indicate that the ions once formed have the tendency to
recombine and form molecular acetic acid.

3. Electricity and Chemical Change
> A chemical change may be produced by passig electricity through a solution. The
process is called electrolysis. An electrochemical cell consists of two electrodes and an
electrolyte. There are two types of electrochemical cells –Voltaic cells and Electrolytic
cells. Voltaic cells (also called galvanic cells) produce electric energy from spontaneous
chemical changes. Electrolytic cells produce nonspontaneous chemical changes by
having an external source of electric energy.
Electrolytic Cells
There are several ions present in solution:
>From sodium hydroxide – Na+ (aq), OH_ (aq)
>From water
– H+ (aq), OH_ (aq)
Water is only very slightly ionized. In pure water, the [H+] and [OH+] ions are
both equal to 1 x 10_ 7 mole/L. To increase the conductivity of water, an electrolyte
(salt, base NaOH) or an acid) is added to the solution. The stainless screw nails are
passive electrodes, that is, they do not take part in the electrode reactions, the
positive electrode is called the anode. The negative electrode is called the cathode.
Anode reaction: 4 OH _ (aq)
Cathode reaction: 4 H+ (aq) + 4 e _
2 H2O (l) + O2 (g) + 4 e _
2 H2 (g)

4. Dry Cell Battery
This simple dry cell battery
contains a negative electrode
(a zinc sheath which encloses
the battery materials) and a
positive electrode (the carbon
rod and the carbon and
manganese dioxide mixture
that surrounds the rod). An
electrolyte paste separates the
two electrodes and facilitates a
chemical reaction between
them. This reaction causes a
current to flow (that is, makes
the electrons move) through a
conductor that connects the
positive and negative
electrodes.
Cell reaction: 2 H2O (l)
2 H2 (g) + O2 (g)
Voltaic reaction
A fuel cell is an example of a voltaic cell. This cell produces electrical potential
(emf) as a result of chemical reactions taking place inside it. In other words, this
cell converts chemical energy into electrical energy. An electrolytic cell does the
opposite. Fuel cells should run forever,as long as the two reactants are supplied
continuously, electricity will be produced.

5. Corrosion, an Electrochemical Process
Corrosion involves the destructive reactions of substances (usually metals and
building materials) with substances in their environment. Acids, oxygen, moisture,
or environmental pollutants such as chlorides, dust, sulfur dioxide, and nitrogen
oxides may react with metals. The corroded material looses its shape and eventually
goes to waste. An example of corrosion is the direct combination of metals with
oxygen in the air. This can take place in a dry or wet atmosphere.
At room temperature, almost all metals except gold and platinum are covered
with an oxide film. Unprotected iron protects with oxygen in air, producing rust
(Fe2O3).Rust is flaky and porous. PbO2 covers and protects the underlying metal
from further attack.
Bimetallic Corrosion
When two different metals are in contact in a wet atmosphere, an
electrochemical cell forms. One metal becomes the anode and corrodes as it oxidizes.
The other metal serves as the cathode. The phenomenon is called bimetallic corrosion.

6. Metal Protection Technology
Anodic or sacrificial coatings –are metals that are more easily corroded than
the metal protected. Galvanized steel is zinc coated on steel (iron, nickel,
chromium alloy).
Cathodic or Noble coatings-are metals that are less easily corroded than the
metal protected. Tin cans are familiar food containers.
A layer of aluminum oxide may be deliberately coated on aluminum metal by process
called Anodizing . This oxide layer protects the metal underneath from further
corrosion.
Metal parts in cars, refrigerators, or bathroom fixtures may be chrome-plated. This
provide s both protective and decorative functions. This plate is hard and corrosionresistant, with high polish and a bluish luster.

7. Lesson B: Colligative Properties of Solutions
Colligative properties –are properties of solution that depends only
on the quantity of solute present but not on the kind of solute.
a. Boiling point – the temperature at which the vapor pressure of a
liquid is equal to the external pressure. The boiling point of pure
water is 100
b. Freezing point – the freezing point of pure water is 0 or 32
4 Kinds of Colligative Properties
1. Vapor Pressure of solution – is always lower than the vapor
pressure of pure solvent.
2. Boiling Point Elevation – is greater than the boiling point of pure
solvent
3. Freezing Point Depression – is lower than the freezing point of pure
solvent
4. Osmotic Pressure - a pressure produced by osmosis.

8. Vapor Pressure
Is the pressure of the gas phase of a substance while in contact with the
liquid phase. Note that we use the term vapor to denote the gas phase of a
substance that is solid or liquid at room temperature. The term gas is used for
substances already in the gas phase at room temperature (e.g., oxygen gas, carbon
dioxide gas).
Condensation
Some gas molecules can collide with surface molecules in the liquid
phase and become liquid again, this process is called Condensation.
Vapor Pressure Lowering
This is especially important for gas solutions. If there are two components, x1 and x2
represent the mol fractions of components 1 and 2 respectively.
x1 =
n1
n1 + n2
x2 =
n2
n1 + n2
For a solution, the mol fraction of the solute (xsolute) is the ratio of the number of moles
of solute to the total number of moles and solvent in solution.

9. Raoult’s Law
Suppose P is the vapor pressure of the pure liquid solvent and P is the vapor pressure
of the solvent when a solute is added:
P = the vapor pressure of the pure liquid solvent, and
P = the vapor pressure of the solution
Francois Marie Raoult (1830- 1901), a French physicist and chemist studied the effect
of different concentrations of added solute to the vapor pressure of a pure solvent. He
found out that the more solute he added to a fixed amount of solvent, the lower the
vapor pressure became. In mathematical form, Raoult’s law is written as:
P= P (xsolvent)
P = P (xsolute)
Solutions which obey Raout’s law at any concentration are described as ideal solutions.
Boiling Point Elevation
 is the temperature at which the vapor pressure of a liquid is equal to the external
pressure. Heating increases the temperature and makes the molecules move faster,
resulting to a corresponding increase in the vapor pressure of the solvent. When the
vapor pressure is equal to the external pressure, the liquid starts to boil.

10. Freezing Point Depression
Makers of homemade ice cream add table salt to lower its temperature so the ice
cream will freeze.
In order for a liquid to freeze, its molecules must come together. For the pure solvent
(water) at the freezing point, the solvent solidifies and the temperature remains
constant as long as there is remaining part of the liquid that has not frozen.
At the freezing point of the pure solvent:
Liquid Solvent
Solid Solvent
At the freezing point of the solution:
Liquid Solution
Solid Solvent
Osmotic Pressure
Osmotic Pressure is defined as the pressure that must be applied to a solution to
prevent any increase in its volume by the transfer of pure solvent through a
semipermeable membrane.,
Inside the plant cells is a water solution of different nutrients. The plant cell
membrane allows only certain substances to pass through it. It permits the passage of
solvent molecules but not that of the solute molecules. We describe it as
semipermeable. There is a net movement of solvent molecules from the solvent side to
the solution side. This phenomenon is what we call Osmosis.

11. Reverse Osmosis
If we exert an amount of pressure on the solution greater than that needed to
osmosis, what happens? Reverse osmosis will occur. We will be able to push water in
the opposite direction that it wants to go. The water is almost literally squeezed out of
the salt solution through the membrane. Reverse osmosis is used to remove salts from
seawater so as to produce potable water for drinking and irrigation.
Solutions of the same osmotic pressure are described as Isotonic solutions.
Hypertonic-Shrunk
Isotonic-Normal
Hypotonic-Swollen

12. Did you know that . . . .
Lithium ( Li) can alter how you think
and has been known to “cure”
certain mental illnesses. In fact, lithium is
used in a lot of psychoactive drugs.