TOPIC 2: HARDNESS OF WATER The Concept of Hardness of Water The Concept of Hardness of Water Explain the concept of hardness of water As water flows over the land, it dissolves many mineral substances. The dissolved minerals are deposited together with water in rivers, lakes and oceans. Water is said to be hard if it contains some specific type of dissolved minerals. It is important to note that not all dissolved salts make water hard. As you learned early, water is treated in water purification plants before being piped to your home. The treatment removes only the insoluble particles…
Author: Msomi Bora
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TOPIC 1: CHEMICAL EQUATIONS A chemical equation is a representation of a chemical reaction with the help of symbols and formulas of the substances involved in the reaction. It is a chemical shorthand for representing the reacting substance or substances combining (the reactants) and the substance or substances formed as a result of the reaction (the products). Molecular Equations A Molecular equation is the one which shows the reactants combining and the products formed, in their elemental or molecular forms in a chemical reaction. An example of a molecular equation is the reaction between sodium and water to produce sodium…
TOPIC 7: FORMULA BONDING AND NOMENCLATURE Valence and Chemical Formulae The Concept of Valence Explain the concept of valence Valency is the capacity of an atom to combine with one or more atoms to form a molecule or compound. Valency also refers the number of electrons that an atom can gain, lose or share in forming a chemical bond with another atom. The valency (or combining power) depends on the number of electrons in the outermost orbit (or valency shell) involved in the formation…
TOPIC 6: PERIODIC CLASSIFICATION Constructing the modern periodic table has been a major scientific achievement. The first steps towards working out this table were taken long before anyone had any idea about the structure of atoms. The number of elements discovered increased steadily during the 19th century. Chemists began to find out patterns in their properties. The Law of Triads In 1817, the German scientist Johann Dobereiner noticed that calcium, strontium and barium had similar properties, and that the atomic weight of strontium was halfway between the other two. He found the same pattern with chlorine, bromine and iodine and also…
TOPIC 5: ATOMIC STRUCTURE The Atom We learned early that matter is made up of small, indivisible particles. Everything around us is made of extremely small particles. These particles are either molecules or atoms. An atom is the smallest indivisible particle of an element that takes part in a chemical change. Atoms are the building blocks of matter. All solids, liquids and gases are made of atoms fitted in different ways. The present day chemistry is built on the foundations of the Atomic Theory. The idea that elements are made up of atoms is called the Atomic Theory. An English…
TOPIC 4: FUELS AND ENERGY A fuel is a substance that can be combusted or burnt to release energy as a byproduct. The energy can be in the form of heat, light, electricity, sound etc. This energy can be harnessed to power machines or used for other purposes such as heating or lighting. Combustion is the burning of fuel with energy released as a byproduct. Fuel is a very important substance for the existence of a modern man. Examples of fuels include petroleum products (petrol, diesel, fuel oil, kerosene, spirits, etc), natural gas, coal, wood, charcoal, producer gas, water gas, etc.…
TOPIC 3: WATER Occurrence and Nature of Water The Occurrence and Nature of Water Describe the occurrence and nature of water Water is the most abundant liquid in nature. It is a compound of hydrogen and oxygen. It occurs on land as seas, oceans, rivers, springs, wells, etc. It also occurs in the atmosphere as rain, water vapour, clouds, etc. Water is the essential constituent of animal and plant life. Without water, no life could exist on earth. All living things need water to survive. About 60% of the human body by mass is made of water. A human being…
TOPIC 2: HYDROGEN Hydrogen is the lightest of all the elements. There is very little hydrogen in the earth’s atmosphere. Hydrogen is so light that its molecules are not held by the earth’s gravity and they diffuse into space. Overall, it is the most common element in the universe. It is probable that is forms about 90% of the total mass of the universe. It is believed that the sun composes almost of hydrogen and helium. Hydrogen occurs naturally in air as hydrogen gas. It also occurs in combined state in water, acids, petroleum, and natural gas and in almost…
TOPIC 1: OXYGEN Oxygen exists in air to an extent of 21% by volume (or 23% by weight). It is the most abundant element on earth, accounting for ½ the total mass of the earth’s crust. Oxygen is mainly found in combined states as oxides, hydroxides, silicates, sulphates, carbonates, water, etc. Its ease of combination with other elements to form compounds shows that oxygen is a very reactive element. Preparation and Properties of Oxygen Oxygen can be prepared in the laboratory from either hydrogen peroxide solution or potassium chlorate salt. A Sample of Oxygen Gas in the Laboratory Prepare a…
TOPIC 6: AIR COMBUSTION, RUSTING AND FIRE FIGHTING Composition of air Air is a mixture of different gases. The gases that make up the air include nitrogen, oxygen, carbon dioxide, noble gases (argon, helium, neon, krypton and xenon) and a little water vapour. Air may also contain traces of impurities such as carbon monoxide (CO), sulphur dioxide (SO2), hydrogen sulphide (H2S) and other gases. The presence of these gases in air results in air pollution. Table bellow shows the composition of air by volume. The proportion of water vapour and impurities in air is very variable. The Gases Present in…