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

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.

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) 2 H2O (l) + O2 (g) + 4 e _

Cathode reaction: 4 H+ (aq) + 4 e _ 2 H2 (g)

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.

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.

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 corrosion-

resistant, with high polish and a bluish luster.

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.

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 x2 = n2

n1 + 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.

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.

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.

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

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.