All those materials which are added to food to improve its appearance, taste, odour, food values are called food additive. Some food addives are:
(i) Saccharine: It is used as soluble sodium or calcium salt. It is about 600 times sweeter than sugar.
(ii) Vanillin: An aromatic aldehyde used for vanila flavour in custards, cakes, icecream, etc.
(iii) Potassium or Sodium metabisutphite: A common preservative for squashes and acid foods like pickles. It is a reducing agent as well as germicides.
(iv) Benzoic acid: It retards bacterial growth and is metabolised to Hippuric acid which is excreted in urine.
(v) Butylated hydroxy toluene (BHT) and Butylated hydroxy arisole (BHA): These are antioxidants which prevent ageing of food material.
(vi) Sulphuric dioxide: In low concentration it is used for preserving squashes.
Chemicals in Medicines
A 0.2% solution of phenol in water is an antiseptic, a 1% solution is a disinfectant and a 1.3% solution is a fungicide. Chlorine and sulphur dioxide gases are used as disinfectants for living rooms when infected with disease germs and bacteria.
It is a method of curing disease by specific chemicals, i.e., drugs. Some important chemotherapeutic drugs are: (a) Quinine and Chloroquine phosphate for mlaria, (b) Emetine for amoeba, (c) Piperazine against roundwarms and pin worms, (d) Sulphanilamide and other allied sulpha-drugs like sulphadiazine for bronchitis, sore, throat infections and boils, (e) PAS (para-aminosalicylic acid) and INH (iso-nicotinhydrazine or isoniazid) for tuberculosis.
They rbing down temperature in high fever. Common example are: Aspirin (Acetyl Salicylic acid), Phenacetin, Paracetamol, Analgin and Quinine. In Stomach, aspirin generates salicyclic acid which can ulcerate stomach wall and can cause bleeding there from. Calcium and sodium salts of aspirin are more soluble and less harmful.
Tranquilizer and Hypnotic drugs are: Luminal, Seconal, Equanil, Serpasil. Antidepresents or mood elevator drugs Tofranil, Benzedrine, cocain from coca.
Elements, Compounds, Molecule and Atom
Element: An element is a substance which can not be split up into two or more simpler substances by usual chemical methods of applying heat, light or electric energy. An element is made up of atoms, all having the same atomic number. For example, a hydrogen is an element because it can not split into two or more simpler substances.
Types of ele-ments: Elements have been divided into metals and non-metals. All the metals are solids except mercury which is liquid. Hydrogen, oxygen, carbon and chlorine are some of the non-metallic elements. The inert gases like helium, neon, argon etc. are non-metallic. All the non-metals are solids or gases except bromine which is a liquid.
Mixture: A mixture is a substance which consists of two or more elements or compounds not chemically combined together. For example, air is a mixture of nitrogen, oxygen, argon, water vapour etc. Mixtures are of two types (i) Homogeneous mixture (ii) Heterogeneous mixture.
Homogeneous mixture: A homogeneous mixture has a uniform composition throughout its mass. It has no visible boundaries of separation between the various constituents. A mixture of sugar in water is a homogeneous mixture.
Heterogeneous mixture. A heterogeneous mixture does not have a uniform composition throughout its mass. It has visible boundaries of separation between the various constituents. A mixture of salt and sand is an example of heterogeneous mixture.
Compound. A compound is a substance made up of two or more elements chemically combined in a fixed proportion by weight. For example, water (H2O) is a compound made up of two elements, hydrogen and oxygen, chemically combined in a fixed proportion of 1:8 by weight.
Atom: An atom is the smallest particle of an element that can take part in a chemical reaction. There are 106 different kinds of atoms which make out million of the known compounds. Hydrogen, potassium, sodium are few examples of atoms. Modern research has shown that atom can be further divided into smaller fragments like electrons, protons and neutrons. But atom is still regarded as the smallest particle which can take part in a chemical change.
Molecule: Combination of atoms is called a molecule. A molecule is the smallest particle of a substance (element or compound) which has the properties of the substance and can exist in the free state.
Molecules are of two types:
(i) Molecule of an element. The molecule of an element contains two (or more) similar atoms. For examples a molecule of hydrogen element contains 2 hydrogen atoms and is written as H2. Hydrogen (H) is an atom but can not exist freely whereas hydrogen molecule (H2) can exist freely.
(ii) The molecule of a compound. The molecule of a compound contains two (or more) different types of atoms. For example, hydrogen chloride molecule, HCl, contains two different types of atoms, hydrogen atom and chlorine atom.
Atomicity: The number of atoms in one molecule of a substance (element or compound) is known as its atomicity.
For example, Helium ga (He) contain 1 atom per molecule so its atomicity is 1 and its is called monoatomic. Hydrogen gas (H2) contains 2 atoms in one molecule so its atomicity is 2 and is called diatomic. If any element or compound contains three atoms, it is tri-atomic e.g. O3, four-tetra, five-penta, six-hexa, seven-hepta, eight-octa, nine-nona, ten-daca, and so on.
Cathode Rays (Electrons):
The existence of electrons (negatively charged particles) in an atom was shown by J.J. Thomson in 1897 by passing electricity at high voltage through a gas at a very low pressure in a discharge tube. Cathode rays are swarmers of electrons.
Anode or positive rays (Protons):
In a discharge tube, if the cathode used is perforated and high voltage is applied between the electrodes, when the pressure’ within the tube is below 0.001 mm Hg, a new type of rays come through the perforation in the cathode since these rays come through perforation in the cathode, and were initially called canal rays. These are also called anode rays as they move from the anode side through the gas. In a discharge tube, when the gas atoms lose electrons, they acquire a +ve charge and move away from the anode.
|Difference between cathode rays and Anode rays|
|Cathode rays or negative rays||Anode rays or positive rays|
|(1) Negatively charged.|
(2) Common constituents of all matter.
(3) e/m value is constant.
(4) Light particles
Different from different gases. e/m value depends on the nature of gas.
Heavier than cathode rays (particles)
Neutron: The neutron is a neutral particle found in the neucleus of an atom. Atoms of all the elements contain neutron except hydrogen atom which does not contain neutron. The relative mass of a neutron is 1 a.m.u. Neuron has no charge.
X-rays: The X-rays were accidentally, discovered by Rontgen in 1895.
Properties of X-rays:
(i) They travel in a straight line with speed of light.
(ii) They are not deflected by electric or magnetic field which shows that they are not charged particles.
(iii) X-rays can not pass through opaque materials such as bones. (iv) They cause fluorescence in several materials. A plate coated with zinc sulphide becomes luminous when exposed to X-rays.
Uses of X-rays
(i) In surgery: The X-rays are widely used to detect fractures.
(ii) In detective departments: X-rays are used by detective departments to examine the contents of the parcel without opening it, to test the genuineness of gems and diamonds.
(iii) In radio therapy. X-rays are used in the treatment of tumours and cancers in animals and human beings.
|Properties of a, b and g -rays|
+2e units 4 units
1 (can penetrate 10-3 cm thick Al plate,
|b -rays Electron|
1/1837th unit 100(can penetrate 10-1 cm thick Al plate,
radiation of short wave length No charge (i.e., zero)
10,000(can penetrate 10 cm thick plate)
Rutherford’s experiment—Discovery of Nucleus
In 1911, Lord Rutherford bombarded a thin sheet of metal foil (gold foil) with a-particles (He2+), he found that
(A) Most of the a-particles passed through the foil without any deflection. This shows that most of the space inside the atom is empty and hollow.
(B) Some of the a-particles were deflected through various angles while a very small number were actually deflected by as much as 90° or even large angles. This shows that:
(i) There is a very heavy positively charged centre inside the atom. This centre is known as nucleus.
(ii) Since only a very small fractions of the a-particles were defeated through large angles, the nucleus is situated in a very small volume of the atom.
(iii) Since a-particles deflected by the nucleus have an appreciable mass, it means that entire mass of the atom lies inside the nucleus.
Valence electrons: Those electrons of an atom which take part in chemical reactions are called valence electrons are located in the outermost shell of an atom.
Relation between valence electrons and chemical properties:
(a) Elements having the same number of valence electrons in their atoms show similar chemical properties.
(b) Elements having different number of valence electrons in their atoms show different chemical properties.
Valency: The valency of an element is defined as its combining capacity with other elements. In terms of electrons, the valency of an element is the number of electrons lost, gained or shared by an atom of an element during a chemical reaction.
Atomic Number: The number of protons in one atom of an element is known as atomic number of that element. That is, Atomic number of an element = Number of protons in one atom of the element. In a normal atom (or neutral atom) the number of proton is equal to the number of electrons in it. So we can say – Atomic number of an element = Number of electrons in one neutral atom.
Mass Number: The total number of protons and neutrons present in an atom of an element is known as its mass number i.e., Mass number = No. of protons + No. of neutrons Since the number of protons in an atom is equal to the atomic number of the element, Mass number = Atomic number + Neutron number.
Isotopes are atoms of the same element having the same atomic number but different mass numbers. Isotopes of an element have different mass number because they contain different number of neutrons.All the isotopes of an element have the same chemical properties. The chemical properties of an atom depend on the number of electrons in it.
Radio isotope dating: It is a method of determining the age of rocks, earth and fossils by determining the composition of radioactive isotope. It is based on Half life period of these isotopes.
Half life: It is time required for the decay of one half of atoms present in any given mass of radioactive substance. Radioactive isotopes are used in medicine, agriculture, industry and in many scientific and technological areas.
Carbon dating: The method of determining age of substance containing an isotope of Carbon C-14 is called carbon-dating.
Radioactivity: The radioactivity was discovered by Henry Becquerel in 1896. The substances which gave these rays were called radioactive substances. Thus this property was called radioactivity. Radiation from these substances are : a, b, and g rays
Periodic Table: It is a chart of elements prepared in such a way that the elements having similar properties occur in the same vertical column or group. It is called periodic because the elements having similar properties occur after certain intervals or periods and it is called table because elements are arranged in a tabular form.
Long form or Modern form of periodic table. The modern form of periodic table is based on increasing order of atomic number. General features of the table are as follows:
(i) There are 18 vertical columns which are called groups. They are numbered IA, IB, IIA, IIB...VIIA, VIIB, VIII and 0 (zero).
(ii) There are seven horizontal nows known as Periods.
Alkali metals: The group of elements designated as I A in the modern periodic table e.g.,Lithium, Sodium, Potassium and Cisium.
Alkaline earth metals. The group of elements designated as II A in the modern periodic table e.g., Berrylium, Magnesium, Calcium, Strontium and Barium.
Noble gases: The members of zero group in the modern periodic table e.g., Helium, Neon, Argon, Kryptom, Xenon and Radoni.
Halogens: The group of elements designated as VII A in the modern periodic table e.g., Florine, Chlorine, Bromine and Iodine.
Transition elements: The elements of groups IB to VIIB and VIII in the long form periodic table. Their properties do not follow the regular progression of the periodic table. Elements of group IIB i.e., Zn, Cd and Hg are not true transition elements.
Lanthanides: The 14 elements (from atomic number 58 to 71) immediately following lathanum in the modern periodic table. Their properties are quite alike and are placed in one box only.
Actinides: The 14 elements (from atomic number 90 to 103) following actinium in the modern periodic table. Their properties are quite similar and are placed in one box only.
Metals: Elements that tend to form positive ions. They are good conductors of electricity. They form basic oxides.
Non-metals: Elements that tend to form negative ions. They are poor conductors of electricity. They form acidic oxide.
Metalloids: The name sometimes given to elements that have the intermediate properties between those of metals and non-metals. They form amphoteric oxides.
Electrolysis: The decomposition of an electrolyte by the action of electric current is called electrolysis.
Electrolytic refining: Here a thick block of impure copper metal is connected to the +ve terminal of the battery and this sheet of pure copper is connected to the -ve terminal. Copper sulphate solution is taken as the electrolyte.
Electroplating: The process of depositing a superior metal over a baser metal by using electric current is called electroplating. The aim of plating may be (a) decorator and (b) preservation. The article to be electroplated is thoroughly cleaned and made as cathode while the metal to be deposited serves as anode. The electrolyte is a solution of a suitable salt of the metal to be deposited.
Electrolytes. A compound which conducts electricity when dissolved in water or in molten state is called an electrolyte. e.g., sodium chloride, copper sulphate caustic soda etc.
Non-electrolytes. A compound which does not conduct electricity when dissolved in water or in molten state is called non-electrolyte, e.g., benzene, cane sugar etc. Such compounds contain covalent bonds, they do not ionise when dissolved in water.
Electrochemical cell: A device in which a redox reaction is utilized to get electrical energy is known as electro-chemical cell. The electrochemical cell is also commonly referred to as voltaic or galvanic cell. The electrode where oxidation occurs, is called anode; while the electrode where reduction occurs is called cathode.
Daniel cell: It consists of zinc electrode dipping in sulphate solution where oxidation takes place; and a copper electrode dipping in copper sulphate solution where reduction takes place. The two solutions are separated by a porous pot. The two solutions can sweep through the pot and so come in contact with each other automatically. This porous portion acts as a salt bridge.
Dry Cell: It consists of (i) a negative zinc rod (ii) a positive carbon electrode surrounded by manganese dioxide and (iii) paste of ammonium chloride and zinc chloride as an electrolyte.
Metallic Corrosion: The gradual eating away of metals when exposed to the atmosphere is known as corrosion. The red or orange coating that forms on the surface of iron when exposed to air and moisture is called rust and this gradual process is called rusting. Rust is chiefly a mixture of ferric hydroxide and ferric oxide.
The process of corrosion is speeded up when two metals are in contact with each other. The metals form electro-chemical cell in presence of moisture and the more active forms compounds.
Rusting of Iron. Rusting is a mixture of Ferric oxide and Ferric hydroxide. A coating of rust is formed on the surface of iron in the presence of moisture and air.
Methods of preventing rusting of iron
(i) By covering its surface with paints, grease, enamels and lacquers.
(ii) By galvanization. As long as some zinc coating remains, iron will not rust. This type of coated iron is called galvanized iron or G.I.
(iii) By coating its surface with metals like tin, chromium, nickel and aluminium. These metals are more resistant to corrosion.
A material or substance, that burns to provide energy, is called a fuel, e.g., wood, coal, petrol, kerosene, diesel, liquified petroleum (LPG), solar energy and nuclear energy are new sources of energy.
Coal: Coal is a highly complex mixture of carbon compounds and free carbon. Some nitrogen, sulphur compounds are also present in the coal. It is found in coal mines, situated deep under the surface of earth.
Carbonisation of Coal: When coal is heated to a temperature above 1000°C in the absence of air (or destructively distilled), volatile matter escapes out and a dense, strong mass, called “coke” is left behind. This process of preparing coke from coal is known as carbonisation of coal.
Products obtained by dry distillation of coal: Coal is heated at temperatures above 1000°C in absence of air in a vessel. The gases produced are passed through water. The process gives the following three products:
(i) Coke: A dense, strong residue left in the heating vessel.
(ii) Coal tar.
(iii) Ammoniacal liquor (solution of ammonia)
(iv) Coal gas
The common varieties of coal are:
(i) Lignite (ii) Anthracite (iii) Bituminous
(i) Lignite. It is the brown variety of coal. It contains 30% carbon, 25% volatile matter and 40% moisture.
(ii) Anthracite. It is also called hard coal. It contains 92% carbon, 5% volatile matter and 3% moisture.
(iii) Bituminous. It is also called soft coal. It contains about 80% carbon. It is used for domestic purpose.
Fossil fuels: Coal, petroleum and natural gas are examples of fossil fuel. These are formed in nature due to the decomposition of animals and plants which have remained embedded inside earth’s crust due to geological changes.
Biogas: It is produced by the degradation of biological matter by the bacterial action (of anaerobic bacterias) in the absence of free oxygen.
(i) Natural gas is a biogas, which results after a long period decay of animal and vegetable matter buried inside the earth.
(ii) Gobar gas (or dung gas), which is produced by the anaerobic fermentation of cattle dung.
(iii) Biogas can also be produced from the sewage waste and other organic wastes.
Petroleum: It is a dark coloured liquid with a characteristic smell. It is lighter than water and insoluble in it. It consists of a mixture of hydrocarbons whose composition varies from place to place.
Fractional distillation of crude oil: Petroleum (crude oil) which is a complex mixture of hydrocarbons, is converted into a variety of usable products by fractional distillation.
Liquid petroleum gas (LPG): The gas leaving from the top of the fractionating column of an oil refinery contains hydrocarbons, ethane, propane and butane. Butane is the chief constituent. This gas mixture gets condensed under pressure. This condensate is known as liquid petroleum gas (LPG), and is supplied in cylinders under high pressure. The calorific value of this gas is very high (50 kg per gram).
Natural gas: The crude oil occurs deep below the earth’s crust and often floats on salt water. The oil is covered by an atmosphere of the more volatile (low boiling) hydrocarbons. This gaseous mixture is known as natural gas. This contains mainly lower hydrocarbons. It can be directly used as a fuel. The natural gas is a very cheap raw material for petrochemicals, and fertilizers. It also finds good use for electricity generation.
Petrochemicals: Petrochemicals are the substances which can be obtained using various fractions of petroleum as raw material. For example, the natural gas and benzene are the most valuable raw materials.
Cracking: It is the decomposition of higher hydrocarbon molecules into lower hydrocarbons of lower molecular mass.
C10H22 → C8H18 + C2H4
Fuels in rockets: These are called propellants because they supply enough energy for propulsion of rockets in space.
Characteristics of good propellant:
(i) It should produce a large volume of gases for each gram of fuel burnt.
(ii) Combustion must take place at high rates.
(iii) No residue should be left behind after the fuel is burnt.
Commonly used propellants:
(i) Solid propellants – These consist of a mixture of hydrocarbon and an oxidiser like chlorate, perchlorate or a nitrate. For example, a mixture of aluminium powder, polybutadiene acrylic acid, aluminium perchlorate and a suitable additive (which binds the fuel and the oxidant).
Liquid propellants: These are mixtures of fuels like alcohol, liquid hydrogen, hydrazine etc. mixed with oxidising agents such as liquid oxygen and hydrogen peroxide. For example, a mixture of methyl hydrazine and the oxidiser dinitrogen tetraoxide was used in Apollo rocket which flew man to the moon.
Calorific value of fuel: It is defined as the amount of heat produced in Joules when one gram of it is completely burnt.
Calorific value of hydrogen 150kj/g
Calorific value of methane. 55kj/g
Ignition/kindling temperature: Ignition temperature is the lowest temperature under normal pressure, upto which the combustible substance must be heated in order to start combustion. This is also known as kindling temperature. The substances which catch fire easily have low kindling temperature. For example, yellow phosphorus has a kindling temperature of 35°C. Substances having high kindling temperature need initial heating.