. In a school laboratory: (i) An acid may be defined as a substance that turns litmus red. (ii) A base may be defined as a substance that turns litmus blue. Litmus is lichen found mainly in West Africa. It changes its colour depending on whether the solution is in basic/alkaline or acidic. It is […]
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(A) PHYSICAL PROPERTIES OF ACIDS Acids have a characteristic sour taste Most acids are colourless liquids Mineral acids are odourless. Organic acids have characteristic smell All acids have pH less than 7 All acids turn blue litmus paper red, methyl orange red and phenolphthalein colourless. All acids dissolve in water to form an acidic solution.
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A physical/temporary change is one which no new substance is formed and is reversible back to original. A chemical/permanent change is one which a new substance is formed and is irreversible back to original. The following experiments illustrates physical and chemical changes (a) Heating ice Place about 10g of pure ice in a beaker.
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METHODS OF SEPARATING MIXTURES Mixtures can be separated from applying the following methods: (A) DECANTATION Sediments can be separated from a liquid by pouring out the liquid. This process is called decantation. Experiment Put some sand in a beaker. Add about 200cm3 of water. Allow sand to settle. Pour off water carefully into another beaker.
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CLASSIFICATION OF SUBSTANCES Substances are either pure or impure. A pure substance is one which contains only one substance. An impure substance is one which contains two or more substances. A pure substance is made up of a pure solid, pure liquid or pure gas. A mixture is a combination of two or more pure
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(a) Chemistry is used in the following: (i) Washing/cleaning with soap: Washing/cleaning is a chemical process that involves interaction of water, soap and dirt so as to remove the dirt from a garment. (ii) Understanding chemicals of life Living thing grow, respire and feed. The formation and growth of cells involve chemical processes in living
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CHEMISTRY LABORATORY AND APPARATUS Chemistry is studied mainly in a science room called a school chemistry laboratory. The room is better ventilated than normal classroom. It has electricity, gas and water taps. A school chemistry laboratory has a qualified professional whose called Laboratory technician/assistant. All students user in a school chemistry laboratory must consult the
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WATER ON EARTH Water is an important item in our universe. We need water for transport (lakes and oceans), Generation of power, (hydroelectricity), drinking industrial processes, manufacturing and cooling among others. Very little of the world’s water is fresh (2.6%). Most of it (97.4%) is in oceans. Most of the fresh water is frozen (76%).
INTRODUCTION TO CHEMISTRY Chemistry is a branch of Science. Science is basically the study of living and non-living things. The branch of science that study living things is called Biology. The branch of science that study non-living things is called Physical Science. Physical Science is made up of: (i) Physics– the study of matter in
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OXYGEN (O2) PROPERTIES AND USES Oxygen (O2) is an active, life-sustaining component of the atmosphere; making up 20% by volume of the air we breathe. It is colorless, odorless and tasteless. Oxygen is the most widely occurring element on earth. Because it forms compounds with virtually all chemical elements except the noble gases, most oxygen
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Corrosion The eating up of metals by the action of air and moisture on their surface is called corrosion. The corrosion of iron is called rusting. While other metals are said to ‘corrode’, iron metal is said to ‘rust’. Rusting of Iron When an iron object is left in damp air (or water) for a
WATER AND HYDROGEN Hydrogen is the simplest element. It is the first element in the periodic table, and it is placed in Group I of the periodic table. Hydrogen Occurrence Hydrogen is the lightest element and the most abundant element in the universe. Hydrogen occurs naturally as a mixture of the three isotopes: Protium,
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INDICATORS Red cabbage juice solution works well instead of universal indicator solution. Making Cabbage Indicator Acid base indicators are chemicals that change colour in the presence of different pH levels. These are usually larger organic molecules. Some, like that in purple cabbage, are natural. You will be making an acid base indicator from purple
COMPOUNDS AND FORMULA A compound is a pure substance formed by chemically combining at least two different elements. Compounds are two or more different elements combined. Their atoms have been joined or bonded together. Compounds can be represented by a FORMULA. There must be at least two different types of atom (elements) in a
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SEPARATION OF MIXTURES Sometimes we need pure substances as opposed to impure ones. You can imagine a mixture of sand and table salt and imagine how much use you would have for it. or imagine the manufacture of drugs and medicines. Purity is highly essential here as it is crucial to our well-being and health.
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DISTINCTION BETWEEN COMPOUNDS AND MIXTURES The following example of iron, sulphur and iron sulphide will make us understand the difference between mixtures and compounds. Properties of Iron and Sulphur The following experiment shows the difference in properties between the elements iron and sulphur. Preparation of a Mixture of Iron and Sulphur Take about
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CONSTITUENTS OF MATTER Atoms, Molecules, Elements and Compounds The Atom An atom is the smallest particle of a substance which can have its own characteristic properties. Atoms are built up of even more fundamental sub-atomic particles. These are electrons, protons and neutrons. The protons and neutrons are in the nucleus (centre) of the atom and
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CONDUCTORS AND INSULATORS The ability to conduct electricity is the major simple distinction between elements that are metals and non-metals. Electrical Conductors A conductor is a material that conducts electricity but is not chemically changed in the process. They carry an electric current through freely moving electrons when a potential difference is applied across
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Pure Substance Pure means that only one substance is present in the material and can be a pure element or compound. A simple physical test for purity, and properties that can help identify a substance, is to measure the boiling point or melting point. Every pure substance melts and boils at a fixed temperature.
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CONDUCTORS AND NON-CONDUCTORS All metals (copper, iron, lead, magnesium etc) and graphite, a non-metal. Most non-metals (sulphur, iodine, charcoal etc.) Most solid compounds (All gases are non-conductors) Liquids are classified in three groups as regards their conductivity of electricity: (i) Those that pass an electric current and are not decomposed by if (conductors) (ii)
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