Understand Exothermic and Endothermic Reactions. Click on the Link to Watch the VIDEO explanation:
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Reactions that release heat are call exothermic reactions. Reactions that absorbs heat are called endothermic reaction. Lighted candle and firecracker are example of exothermic reaction. They release heat due to chemical reaction taking place in them. Evaporation of water from any water body is due to absorption of heat. The blue coloured hydrated copper sulphate decomposes to white anhydrous copper sulphate and finally to black copper oxide on continuous heating. Such reactions that require heat energy are called endothermic reactions. Combustion reactions are exothermic reactions. Click on link. When a small piece of carbon heated to red hot and introduced in a jar with oxygen it catches fire and burns liberating CO2 and Heat. When phosphorous after heating in introduced in a oxygen gas jar it catches fire and burns with dense fumes liberating phosphorous pentaoxide and heat. You can see water being heated in pan. On heating water converts to steam. Graphite, an allotrope of carbon can be converted to diamond by heating graphite under very high pressure. This is an endothermic reaction. The differences between Exothermic and Endothermic reactions are listed here
Understand Enzyme Reaction. Click on the link to Watch the VIDEO explanation: Watch Video
The activation energy increases the kinetic energy of the system and brings about precise and forceful collisions between the reactants. Enzymes lower the activation energy requires for the reaction. This is achieved in two ways. By bringing the reactant molecules closer favouring the precise collision. By electrophellic and nucleophillic attack developing strain in the bond of the reactants.
Understand the Electrolysis of Water. Click on the link to Watch the VIDEO explanation:
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The electrolytic cell used for electrolysis of water is called Hoffman's Voltmeter. Acidulated water is the electrolyte taken in the limbs of the voltameter. The electrodes are made of Platinum. Anode is connected to the positive terminal of the battery and cathode to negative terminal. On the passage of current water dissociates into hydrogen ions and hydroxyl ions. At cathode discharged hydrogen atoms from hydrogen molecules. At anode hydroxyl ions are discharged that forms water and oxygen gas. Oxygen and Hydrogen are collected in the limbs of voltameter. The amount of hydrogen collected is double the amount of oxygen. here are the reactions that takes place.
Understand Dumas method for estimation of nitrogen. Click on the link to Watch the VIDEO explanation:
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Understand what is Dry Cell. Click on the link to Watch the VIDEO explanation: Watch Video
A cell is the simplest unit for making electricity. It generates electricity from chemical reaction. It pumps electrons along wires. Two or more cells forms a battery. Substances dissolved in water such as acid which from charged particles such as positively charged cation and negatively charged anion, these type of solutions forms the electrolyte of the cell. Metal rods immersed in electrolyte act as electrode. Positive electrode is the anode and negative electrode is cathode. These electrodes attracts opposite charges resulting in flow of electrons. A French engineer George Leclanche invented battery which bears his name. His invention which was quite heavy and prone to breakage has improved over the years. In slightly different form, Leclanche cell is now being produced in great quantities and used in many devices like flashlight and portable radios. But, it was Carl Gassener of Mainz who is credited with constructing the first commercially successful dry cell(Zinc carbon cell) in the year 1881. Variation follows, by 1889 there were at least six dry cell batteries in circulation. The dry cell is the modification of wet Leclanche cell. Observe the vertically cut section of the cell. The anode is the graphite rod. Graphite is a form of carbon. Zinc container is cathode. The electrolyte is moist jelly like paste of Ammonium Chloride and Starch enclosed in a metal cylinder. A mixture of Manganese dioxide and powdered carbon surrounds the graphite rod. The jelly is prevented from drying by enclosing the top with a pitch. A cardboard washer is used to prevent connection between graphite rod and zinc container. Zinc can is surrounded by an insulating thick paper covering. Positive terminal is the brass knob at the top while negative terminal is the base. The simplifies reactions which take place inside cell is given here. This dry cell produces a voltage of about 1.5V. Button cell and Nickel Cadmium cell are better versions of dry cell. Nickel cadmium cells are rechargeable cells.
Understand Deoxyribonucleic acid or DNA. Click on the link to Watch the VIDEO explanation: Watch Video
DNA or Deoxyribonucleic acid is an information rich molecule that has laid the foundation of a new branch of science, Molecular Biology. Click on the links provided here. Here you can get the sense where DNA resides in a cell. A double stranded DNA is organised into chromosomes situated in the nucleus and the membrane bound nucleus is found in the cell. Structure of DNA is comparable to a twisted ladder. This double helical structure is proposed by James Watson and Francis Crick in 1953. A rotating wire frame model of Watson Crick DNA double helix is shown here. Main structures and features of DNA are shown here. The Sugar and Phosphate backbone is on the outside of double helix whereas Nitrogen basis are stacked inside. The two strand of helix are held together by specific base pairing. An Adenine molecule in one strand is paired with Thymine in other strand, Guanine is paired with Cytosine. One complete turn of a helix has ten base pair. The pattern of base pairing i.e. AT and GC is consistent with the known composition of DNA. Hydrogen bond are present between specific base pair. This animation demonstrates the mechanism of base pairing. Note the specific ways in which different Nitrogen base are paired. The AT pair is formed by two hydrogen bond while the GC pair has three hydrogen bonds. Some momentous events in the evolution of Heredity and Genetics are listed here. Click on the link for the event.
Understand Distillation. Click on the link to Watch the VIDEO explanation: Watch Video
Distillation is the process of heating the liquid to form its vapour and then condensing the vapours to form liquid again. It is used to separate two or more substances present in a liquid or for purification of water. The apparatus used is shown here. Take some salt water in a retort and heat it till it gets converted into steam. The steam is collected in a beaker which is connected to retort as shown here. The steam condenses into drops of water and the salt is left behind in the retort.
