Ordinary Level Chemistry Note is available now for all science students in various African countries, especially for students preparing for any official exams as a revision tool. This article consists of the following topics you are to study here which are; INTRODUCTION TO CHEMISTRY, Importance of chemistry, LABORATORY, Characteristics of chemical changes, ELEMENTS, THE ATMOSPHERE AND COMBUSTION, GAS GENERATION AND COLLECTION, ATOMIC STRUCTURE, BONDING AND STRUCTURE, CARBON AND ITS COMPOUNDS, MOLE CONCEPT, Titration, SULPHUR AND ITS COMPOUNDS, ENERGY CHANGES IN CHEMICAL REACTIONS (THERMO CHEMISTRY), ORGANIC CHEMISTRY, Molecular and structural formulae, ALKANES, ALKENES, ALKYNES
INTRODUCTION TO CHEMISTRY
Chemistry is a branch of science that deals with the study of structure, composition
and properties of matter. Chemistry as an experimental subject relies on:
- Careful handling of apparatus
- Carrying out chemical tests or chemical analysis
- Making critical observation
- Critical reporting of observations
- Drawing appropriate conclusions from observations
Chemistry as a practical science tries to answer the following question.
What are materials made up of?
How is matter formed?
How does matter behave?
Why does matter behave the way it does?
There are quite a number of branches of chemistry such as Organic chemistry,
Physical chemistry, Inorganic Chemistry and Analytical chemistry.
Importance of chemistry
- The knowledge of chemistry makes us to understand the properties of substances
and handle these substances with great care. Some may be poisonous, corrosive,
toxic etc. - Makes us to understand how to extract substances from the earth and use them
e.g. gold, copper etc. - Chemistry knowledge opens up way to science professional courses such as
medicine, education and pharmacy. - The knowledge of chemistry makes us to know the effects of chemicals on the
environment and subsequently puts us in position to protect our environment. - Broad knowledge in chemistry puts us in better positions to contribute towards
more advancement in science and technology for better and quality human life. - The knowledge of chemistry is relevant in many ways such as making of food
supplements, distillation of fuel, making of plastics, making cosmetics and dental
creams, manufacturing of soap and detergents, making insecticides and
herbicides.etc.
LABORATORY
A laboratory is a special place with special equipments where scientific investigations
or experiments are carried out. A laboratory is a place of adventure and discovery;
in fact some of the most exciting events in the history of science have taken place in
laboratories e.g. the discovery of oxygen.
When experiments are carried out in the laboratory, chemical materials and are used.
Chemicals are substances usually in solid or liquid forms that are consumed during
reactions. They get used up in reactions during the course of an experiment. E.g.
Sodium hydroxide and Hydrochloric acid.
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Apparatus are scientific tools that are used in carrying out scientific experiments.
They are not used up or consumed and can be used repeatedly. E.g. Beaker.
Laboratory safety rules
- Do not enter the laboratory without permission.
- Perform only the experiments assigned by the teacher.
- Learn at once the location and operation of fire extinguishers and other first-aid
materials. - No equipment should be used until proper instructions are received from the
teacher and you have proven proficiency. - Avoid unnecessary movements in the laboratory.
- Do not play about with electrical or gas devices.
- Handle apparatus with great care.
- In case of accidents such as burns, cuts or splash of chemicals, wash with plenty
of water and report to the teacher or laboratory technician. - Do not taste or smell gases continuously.
- Do not eat or drink anything in the laboratory.
- When heating using boiling tubes or test tubes, do not turn the open end towards
yourself or anyone. - Whenever in the laboratory, use clean and dry apparatus.
- Never use faulty equipments. Check and make sure that the devices you are given
are not damaged. - Never dispose off solid material into sinks instead throw them in solid waste
containers or pits. - Always make sure that you follow instructions that are given and read labels on
bottles making sure that you use correct reagents. - Do not leave reagent bottles open. As soon as you finish using a bottle, put its
stopper and return it to its right position. - Do not keep your workspace too congested.
Simple laboratory equipments or apparatus
In order to carry out experiments in the laboratory, we need special tools such as
a measuring device. Such a tool is referred to as an apparatus.
The Bunsen Burner
This is a piece of apparatus that is used for heating substances in the laboratory.
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Structure
Functions of the labelled parts
Chimney/barrel: is a long metallic pipe through which the gas passes to be lit.
Collar/metal ring: is a metallic ring with a hole in it that regulates the amount of air
entering the air hole.
Jet: is a tiny hole through which the gas enters the chimney. It is narrow so that the
gas enters the chimney at high pressure.
Gas inlet: it connects the Bunsen burner to the gas supply.
Base: it is a heavy metal and used as a stand for the Bunsen burner i.e. it supports
the Bunsen burner in an upright position.
How to light a Bunsen burner
- Connect the Bunsen burner to the gas tap.
- Close the air hole.
- Open the gas on fully.
- Light the Bunsen burner at the top of the chimney.
- Open the air hole to get a hot non luminous flame used for heating.
Bunsen burner flames
A flame is a burning gas that produces heat and light. A Bunsen burner produces two
types of flames i.e. luminous and non luminous flames.
Luminous flame
This type of flame is produced when the air hole of the Bunsen burner in closed. The
flame is large, bright, yellow and not very hot. Examples of luminous flame include;
candle flame, bush fire flames and lantern flame
Zones of a luminous flame
The luminous flame has four zones namely:
- Dark zone/ zone of un burnt gas; burning of the gas does not take place here, it
is dark and cool. - Luminous yellow zone; the gas burns in this zone but not completely because of
limited air. Tiny particles glow in this region to give out light. - Thin outer zone; the zone is colourless and gas burns completely due to plenty of
air. - Blue zone; this zone receives plenty of air and burning is more complete than in
luminous zone.
Non luminous flame
This is the flame produced when the air hole of the Bunsen burner is open. Air enters
through the air hole and mixes with the gas. This makes the gas to burn completely
producing a very hot flame used for heating. The flame does not produce soot.
Examples of non luminous flame include; gas cooker fame and stove flame.
This type of flame has three zones namely:
- Dark zone/zone of unburnt gas; the zone is dark and the gas does not burn. It is
therefore cool. - Blue-green zone; the gas here burns but not completely due to insufficient supply
of air. - Purple/pale blue zone; burning of the gas take place completely as there is plenty
of air, making this region very hot.
Differences between luminous and non-luminous flames
| ELEMENTS OF COMPARISON | LUMINOUS FLAMES | NON-LUMINOUS FLAMES |
| Flame Color | The flames bright yellow in color. | The flames are light blue in color. |
| Soot | They are sooty (produce soot) | The flames are not sooty (does not produce soot). |
| Production On Bunsen Burner | In a Bunsen burner, luminous flame is formed when the air-hole is completely closed. | In a Bunsen burner, non-luminous flames are formed when the air-hole is opened. |
| Heat Production | They are not very hot (produce less heat). | The flames are very hot (Produce more heat). |
| Light Production | They produce more light. | The flames produce little light. |
| Nature | Flames are not steady (do not burn steadily). | Flames are steady. |
| Burning Characteristic | The flames do not burn more efficiently. Luminous flames do not get enough oxygen to turn all the carbon that is being burnt into carbon dioxide. | Non-luminous flames burn more efficiently because they are able to combine all their carbon with oxygen. |
| Visibility | The flames are wavy and brightly visible. | They are hardly visible and less wavy. |
| Burning Gas | The burning gases have limited access to oxygen. | The burning gases have unlimited access to oxygen. |
| Application | The flames are not used in experiments (not best for laboratory operations) because it is wavy and sooty in nature. | They are most preferably used in experiments (laboratory operations) because they are hot, not sooty, and less wavy and hence easy to control. |
| Examples | Burning wood, candles, Olympic cauldron etc. | Flames of a Bunsen burner when the air-hole is closed, acetylene torches etc. |
Similarities between luminous and non-luminous flames
- Both flames have the dark zone (zone of un burnt gas)
- Both flames have luminous zone where the gas do not burn completely. In this
zone, the carbon particles glow to give out light. - Both flames have the non luminous zone where gas burns completely.
Strike back
Strike back occurs when the gas burns at the inner point jet or at the air hole instead
of burning at the top of the chimney. It occurs normally when the air hole is left open
when lighting the Bunsen burner. Strike back can cause explosion leading to
destruction of property and lives.
MATTER
Matter is anything that occupies space and has weight. Matter is made up of very tiny
particles known as ions, atoms or molecules.
An atom is the smallest electrically neutral particles of an element that takes part in a
chemical reaction.
A molecule is the smallest electrically neutral particle of a compound or element that
can exist on its own.
An ion is an electrically charged particle of an atom or a group of chemically combined
atoms after losing or gaining electrons.
Matter exists in three state i.e. liquid, solid and gas.
Properties of the states of matter
Solids
- Consist of particles that are fixed together i.e. particles that are not mobile.
- The particles are held by very strong forces of attraction.
- Solids have fixed shape.
- Solids have very high density.
- Solids are practically incompressible.
Liquids
- A liquid has a definite volume but no definite shape i.e. it takes up the shape of the
container in which it is placed. - Particles in a liquid are held together by weak intermolecular forces of attraction
making the particles to move freely to some extent around each other. - Liquids are slightly compressible
- Liquids are less dense compared to solids.
- Particles in a solid are relatively spread apart.
Gas
- Particles in a gas are far apart from each other.
- Particles in a gas are free to move randomly as they have negligible forces of
attraction. - Gases are easily compressible
- Gases have no definite shape and volume.
- Gases are very light.
KINETIC THEORY OF MATTER
Kinetic theory of matter states that;
Particles that make up matter have kinetic energy and they are always in motion. The extent of the movement of the particles depends on the amount of kinetic energy the particles have.
In solids, the particles are held together by very strong intermolecular forces of
attraction; the particles do not have enough kinetic energy to make them move from
one place to another but they can vibrate in their mean position. When a solid is
heated, the kinetic energy of the particles increase as they absorb the heat energy
which weakens the forces of attraction between the particles. When the melting point
is reached, the molecules break free and the solid changes to liquid.
In liquids, the particles are held together by weak forces of attraction. However, they
have enough kinetic energy to enable the particles move from one place to another
within the liquid. When a liquid is heated, the forces of attraction between the
particles are weakened further until when they are completely broken and at this
point, the liquid changes to a gas. This is the boiling point of the liquid.
In a gas, the particles are free to move randomly as they posses much kinetic energy
and the particles are not held together by any particular forces of attraction (or
negligible forces of attraction)
CHANGE OF STATES
The process by which a solid changes into a liquid is the melting. The constant
temperature at which a solid changes into a liquid is called melting point
The process by which a liquid changes into a gas is called boiling or evaporation. The
constant temperature at which a liquid changes into a gas is the boiling point.
The process by which a liquid changes to a solid is freezing or solidification.
The constant temperature at which a liquid changes into a solid is referred to as
freezing point.
The process by which a gas changes into a liquid is called condensation.
The process by which a gas changes directly to a solid is referred to as sublimation
and vice versa.
Summary of the changes of states
Experiments to demonstrate that particles in liquids and gases move
a) Brownian motion: This is the continuous random movement/motion of solid particles in liquids and
gases.
- Demonstration of Brownian motion in Liquids
When pollen grains are poured in water, they are seen to be moving in a
continuous random zigzag manner. The movement of the pollen grain is due to
bombardment of the particles by the moving particles of water. - Demonstration of Brownian motion in gases
When smoke particles are trapped in a glass cell and observed under a microscope,
the particles are seen to be moving in a random zigzag manner. The movement of
the smoke particles is due to bombardment by the moving gas particles.
Or
When a beam of light is directed into a dark room, the dust particles are seen to be
moving in a continuous random manner. The movement of the dust particles is
due to the bombardment of these particles by gas particles.
b) Diffusion: This is the spreading of particles or molecules from a region of high concentration
to a region of low concentration.
- Demonstration of diffusion in liquids
Place a crystal of potassium permanganate in a beaker of water and watch. After
sometimes, the water turns pink due to the particles of potassium permanganate
spreading throughout the water. - Demonstration of diffusion in gas
Open a bottle of concentrated ammonia solution and place the bottle at the corner of
a room. After sometimes, ammonia smell will spread through out the room due to
diffusion of the ammonia particles.
Rate of diffusion of gases
The rate of diffusion of a gas depends on;
- Density of the gas. The lighter the gas, the higher the rate of diffusion.
- Density of the diffusion medium. The lighter the density of the diffusion medium,
the faster is the rate of diffusion. - Concentration gradient. The steeper the concentration gradient, the higher the rate
of diffusion. - Surface area. The smaller the surface area of diffusion, the higher the rate of
diffusion. - Temperature of the diffusion medium. The higher the temperature, the faster is the
rate of diffusion of the particles. - Size of the particles. Smaller particles diffuse faster the larger particles.
- Distance through which diffusion occurs. The smaller the diffusion distance, the
faster is the diffusion.
Expt. to compare the rates of diffusion of ammonia and hydrogen chloride gas
Diagram
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