Understand Exothermic and Endothermic Reactions

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

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

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

Understand Dumas method for estimation of nitrogen. Click on the link to Watch the VIDEO explanation: 
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what is Dry Cell

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.

What is Deoxyribonucleic acid or DNA

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.

What is Distillation

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.

Discovery of cathode ray tube

Discovery of cathode ray tube. Click on the link to Watch VIDEO explanation:
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William Crookes discovered cathode rays when he was studying discharge in electrical gases. Whereas J.J. Thompson discovered that cathode rays consists of negatively charged particles called electrons.

What are the Different types of magnetic substances?

Understand the Different types of magnetic substances. Click on the link to Watch the VIDEO explanation: Watch Video

When we bring a piece of iron near a magnet, it gets attracted to a magnet. Iron and steel are not the only elements which can be magnetized. In fact most of the materials are magnetic. Michael Faraday, an English physicist classified magnetic substances into three classes namely diamagnetic, paramagnetic and ferromagnetic substances. Click on each to know more. Diamagnetic substances are feebly repelled by a magnetic field. E.g. bismuth, lead, mercury, copper, diamond, gold, silver and silicon. If a lead rod is suspend in a magnetic field, it slowly align itself in right angles to the field. Behaviour of diamagnetic substance is independent of temperature. Paramagnetic substances are attracted by a magnetic field. If an aluminium rod is suspend in a magnetic field, it slowly align itself along the field. E.g. aluminium, platinum, chromium, magnesium, tungsten and calcium. Paramagnetic substance when placed in a magnetic field is feebly magnetized in the direction of the field. Temperature has an adverse effect on them. Due to rise in temperature paramagnetic substance tend to lose its magnetism. Ferromagnetic substances exhibit strong magnetic properties. E.g. Iron, cobalt, steel, nickel and Alnico. Ferromagnetic substance when placed in a magnetic field is quickly align itself in the direction of the field and is strongly magnetized in the direction of the field. Temperature has an adverse effect on them. Due to rise in temperature Ferromagnetic substance tend to lose its magnetism.

Understand the difference between Physical and Chemical changes

Understand the difference between Physical and Chemical changes. Click on the link to Watch the VIDEO explanation: Watch Video

Sulphur and Iron are elements. On combining them in the absence of heat they form a mixture. This is a physical change. On heating sulphur combines with iron to form iron sulphide. This is a chemical change. The difference between physical and chemical change may be tabulated here. In a physical change only physical properties like colour, volume changes but chemical properties remain same. In chemical change, the chemical composition and properties undergo a change. Look at the table to find the differences.

Understand the differences between Crystalline and Amorphous Solids

Understand the differences between Crystalline and Amorphous Solids. Click on the link to Watch the VIDEO explanation: Watch Video

There are two main classes of solids namely crystalline and amorphous. Click on the links to know more. Crystalline solids have a regular and repetitive patterns of atoms, molecules or ions. They are symmetrical shape flat smooth and plane faces which meet at a characteristic angle. They are classified as single crystal and poly crystalline crystals. If the periodicity of pattern is extended throughout the pattern then it is called single crystal solid. In poly crystalline crystals the periodicity of the pattern is interrupted at the boundaries. Crystalline solids have sharp melting points and all bonds have same strength. Diamond, rock salt, mica and sugar belong to this category. In amorphous solids, like liquids, the atoms and molecules are not arranged in an orderly manner. But in amorphous solids atoms are rigidly fixed and they are allowed to move as in liquids. Glass is an amorphous solid.

What is the Composition of Alloys?

Understand the Composition of Alloys. Click on the link to Watch the VIDEO explanation: 
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Alloys of copper. Given here are few column alloys on the left represented by rows. The metals that each alloy is composed of are represented by tick marks in respective metal columns. To find out the percentage of metal in that alloy drag your mouse on the respective tick mark. Alloys of aluminium are duralumin and magnalium. To find the percentage of each metal in the alloy click on the respective metal name. Alloys of lead are type metal and solder. To find the percentage of each metal in the alloy click on the respective metal name. Alloys of steel. Rows represent the alloys and column represent the metal they are composed of. The metals that each alloy is composed of are represented by tick marks in respective metal columns. To find out the percentage of metal in that alloy click on the tick mark under respective metal column.

Understand the change in the phases of matter

Understand the change in the phases of matter. Click on the link to Watch the VIDEO explanation: Watch Video

The three phases of matter are solid, liquid and gas. Let us see water go change of phases under different conditions of temperature. Arrange apparatus as shown here. Take some ice in round bottom flask and heat it. Cubes of ice melts to form water which is the liquid state of ice. Continue supplying heat. Water gets converted into steam which is gaseous phase of water. Continue heating till all water converted into heat. Now remove source of heat energy. Steam is being cooled and condensed into water collected in a beaker. This process of conversion of heat into water is called condensation. Now deep freeze the condensed water. We get back the ice. This shows that a solid can be converted to its liquid state and then to its gaseous state by supplying heat and then on removal of heat the process is reversed. Most substances can be converted from one state into another. Wax, iron, gold, silver, copper are some substances that can exist in all three states.

Understand the Chemical Properties of Metals

Understand the Chemical Properties of Metals. Click on the link to Watch the VIDEO explanation: 
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All elements discovered by men have been systematically organised into periodic table. Most of these are metals. Name of some are highlighted. We see only a few metals in pure form. Most of them do not exist in pure or native form. They are highly reactive so react with other elements and disguised. Why are they highly reactive. Metals are all electropositive in nature. This means they tend to lose electron and get positive charge. So they act as strong reducing agent and undergo chemical reaction in their electropositive state. Metals have valence range of 1 to 3. This means they can lose one two or three electrons from their valence shell. All metals are solid at room temperature and reacts easily with gases and liquids. Gases like hydrogen, oxygen and chlorine and liquid like water acid and salt reacts easily with metal. Reactivity of metals with gases. When surfaces of metals like sodium or calcium are exposed to air, after sometime a white coat of oxide forms. Metals react with oxygen in air to form oxide. Sodium forms sodium oxide and calcium forms calcium oxide. When these oxides dissolve in water they form their hydroxides. So such oxide are basic in nature. Colourless phenolphthalein turns pink in hydroxide solution. This is a test of basic nature of hydroxide. Similarly Hydrogen reacts with metal to form Hydrides and chlorine to form chlorides. The reactivity of water varies with nature of metals. Metals that reacts with water can also reacts with acids. For example acids like HCl and H2SO4 reacts with metals to form respective chloride and sulphate salts. A more reactive metal displaces a less reactive metal from its salt solution and takes its place. Zinc is more reactive than copper. So when zinc is placed in copper solution it replaces copper to form zinc sulphate and copper metal is set free.

Understand Guy Lussac's Law of combining volume?

Understand Guy Lussac's Law of combining volume. click on the link to Watch the VIDEO explanation: Watch Video

When two volumes of hydrogen reacts with one volume of oxygen then two volume of steam are formed. Thus the combining volume of the reactants and the volume of product are in the ratio 2:1:2. So Guy Lussac's Law of combining volume states that the combining volume of gasses are in a simple integer ratio to one another and the ratio can be extended to the products if they are gaseous provided all the volume are measured under same condition of temperature and pressure.

What is Charles' Law?

Understand Charles' Law. Click on the link to Watch the VIDEO explanation:
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Gasses have various properties that can be observed by our senses. The gas pressure, temperature, mass and volume are variables that are related to one another. here is an activity to understand the relationship of Volume V and Temperature T of a gas confined at constant Pressure. The no. of moles or amount of gas is constant. The syringe contains fixed no. of moles of a gas at constant pressure. It is air tight fixed to a pressure gauge and a digital thermometer. When the glider is moved the temperature of the gas in syringe changes. Observe the change in the volume of the gas. Record and display Volume and Temperature readings in a table. In 1787 Jacques Charles studied the relationship between volume and temperature of gas. The volume of a fixed amount of gas at constant pressure is directly proportional to its Kelvin temperature. This relationship is called Charles' Law in his honour. Consider an inflated balloon. When liquid nitrogen is poured on its surface, it cools the balloon and its contents to a temperature far below room temperature and the balloon collapses. As the balloon warms up to room temperature it reinflates as the air in the regains the volume it had at room temperature.

Understand Brownian Motion

Understand Brownian Motion. Click on the link to Watch the VIDEO explanation: Watch Video

The first evidence that matter consists of tiny particles in motion was given by English Botanist Robert Brown. When he was studying the pollen grains suspended in a liquid using a microscope, he discovered that pollen grains went dancing to and fro in a random manner. Similar haphazard motion can also be observed when small colloidal particles suspended in a liquid are seen under a powerful microscope. This zigzag motion is due to the unequal bombardment between suspended particles and molecules of surrounding medium. This irregular motion of suspended particles is referred to as Brownian Motion. We shall now study movements of large and small particles suspended in liquids. Let us look at a large particle A suspended in a solution. A no. of molecules hit A from all side. On an average the impact mutually cancelled out. So the resultant force on particle is zero. Now look at particle B which is very small. It is hit by less no. of molecules. Also it is not hit equally by all sides. So there is a resultant force which alters the direction of particle B. When it moves the direction of resultant force also changes resulting in a zigzag motion. Let us look at an experiment. Fill a hollow glass cube with small particles. Placed it under a low power microscope. Simultaneously illuminate the cube with a light source. We observe smoke particles appears as bright particles moving in all directions in black background. This is an experiment of Brownian Motion.

Understand the graphically representation of Charle's law

Understand the graphically representation of Charle's law. Click on the Link to Watch the VIDEO explanation: Watch Video

Here we see gas volume plotted as a function of temperature. The gas shown has a volume of 60mL at about 70°C. When the gas is cooled through a temperature interval of 70° to -100°C its volume drop to 30mL. The volume continues to drop in linear fashion.

Understand Carbon cycle in nature?

Understand Carbon cycle in nature. Click on the link to Watch the VIDEO explanation:
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Here is the representation of carbon cycle in nature. Carbon dioxide is constantly produced by combustion of fuels and by respiration of plants and animals. The amount of carbon dioxide in air however does not increase. This is because during photosynthesis plants takes carbon dioxide and oxygen is given out. It is also removed from the air because it dissolves in rainwater and in seawater. The addition of carbon dioxide in the atmosphere and the removal of carbon dioxide from the atmosphere balance each other. Hence the amount of the carbon dioxide and oxygen its kept constant by the cycle called carbon cycle in nature or carbon dioxide cycle.

Understand how Burning of Magnesium Ribbon is a chemical change

Understand how Burning of Magnesium Ribbon is a chemical change. Click on the link to Watch the VIDEO explanation: Watch Video

Take a piece of magnesium ribbon. Hold one end of it with the pair of tongs and heat the other end over a Bunsen burner or sprit lamp as shown here. The ribbon starts burning with a dazzling light and produces dense white fumes. The white fumes on the cooling form a white powder called magnesium oxide which is a new substance and its properties are different from Magnesium. Can we obtain magnesium back from magnesium oxide by any physical method? Certainly not. Therefore it is a permanent and irreversible change. Hence it is a chemical change.

Understand the representation of Boyle's law graphically

Understand the representation of Boyle's law graphically. Click on the link to Watch the VIDEO explanation: Watch Video

We observe in the Pressure Volume(PV) relationship illustrated here that as the pressure is successively halved from 4 atm to 2 atm and then to 1 atm, the volume doubles and then doubles again. Thus Volume is inversely proportional to Pressure and PV product is always constant.

What is the relationship between Boyle's Law and Breathing

Understand the relationship between Boyle's Law and Breathing. Click on the link to Watch the VIDEO explanation: Watch Video 

What is the relationship between Boyle's law and the mechanics of breathing. Foe a given amount of gas at constant temperature, the volume of the gas varies inversely with its pressure. So observe what Boyle's law has to do with inspiration and expiration of air.

What is Boyle's Law?

Understand Boyle's Law. Click on the link to Watch VIDEO explanation: Watch Video

Do this activity. Take a deep breath, hold on, count 5 and then breath out. Why did the chest expand while we inhale and why did it contracts while we exhales. That's Boyle's law in action. In this module we learn about Boyle's law that concerns about the relationship between pressure and volume of a gas. Air is a gas. Gas has several properties that can be observed with our senses. The gas pressure, temperature, mass and volume are variables that are related to one another. Let us observe what happens when volume and pressure are the variables and temperature and mass of gas are constant. You have a cylinder with a fixed amount of dry gas at constant  temperature i.e. the mass and temperature of gas are constant. The pressure of gas is 4 atm. Observe the volume occupied. Click on weights to reduce the pressure on cylinder. The pressure is now 2 atm. Observe the volume of gas in the cylinder. It has doubled. Reduce the pressure to 1atm. The volume has again doubled. As the pressure is successively halved, the volume doubled. As the pressure reduced the volume increased. Thus volume is inversely proportional to the pressure and the product of pressure and volume is a constant. Mathematically, P*V=k, where V is the volume and k is the Boltzmann constant, k=1.38 * 10^-23 and P is the pressure. Here is another activity to understand relationship between and pressure and volume of a gas confined held at constant temperature. The syringe contains a fixed no. of moles of a gas at constant temperature. It is air tight and fixed to a pressure gauge. When plunger is dragged, the volume of gas varies in the syringe. In the mid 1600 studied the relationship between the pressure P and volume V of a confined gas held at a constant temperature. Boyle's observed that at given temperature the volume of a confined gas with constant mass is inversely proportional to its pressure. The product of pressure and volume is nearly constant at constant temperature i.e. PV=k where k is the Boltzmann constant. At constant temperature let a given mass of gas occupy Volume V1 at pressure P1 and volume V2 at pressure P2. So mathematically P1V1=P2V2. Remember you can use any unit of volume and pressure as long they remain same throughout calculation. This relationship is called Boyle's law in his honour. Now solve a conceptual example. You are at beach resort at sea level. You buy a balloon filled with helium of 4.5L. Atmospheric pressure 100KPa. What will be the volume at pressure of 50KPa. Assume temperature remains constant. It is common knowledge that gases are highly pressurised to make them compact. The action of syringe is another practical application of Boyle's law. When we draw fluids inside syringe, we increase volume inside syringe, decrease pressure inside while the pressure outside is greater. This imbalance forces the fluid inside the syringe. If we reverse the action and put the plunger in, the volume inside is decreased, increasing the inside pressure than outside pressure and fluids are forced out. It can be used to explain the mechanics of breathing. When we breath in air the chest wall expands, increasing the volume of chest cavity. When the diaphragm rises the chest wall contracts reducing the volume of chest cavity thereby expelling the air. This brings about inspiration and expiration. When a vessel containing soap solution agitated bubbles at the bottom of the vessel are seen to increase in volume as they rise gradually to the surface. Why so?

Understand Bomb Calorimeter

Understand Bomb Calorimeter. Click on the link to Watch the VIDEO explanation: Watch Video

For reactions involving gasses such as combustion we use a device called bomb calorimeter. The calorimeter has a water filled insulated box inside which is heart of calorimeter the bomb. The bomb is strong steel container in which exothermic reaction is carried out at near explosive rate and the reactant and product of confine to constant volume. The reactant sample of known mass is taken in a metal cup in the bomb. The bomb is then filled with oxygen at a pressure of 30 atmospheres. The reacted is initiated with an electric ignition wire. Stirrer is used to maintain the constant temperature. The heat of reaction is determined from the temperature rise in the water that surrounds the bomb. The highest temperature recorded by the thermometer is noted. The internal energy change delta E of the combustion reaction is determined using the equation. And the formula as shown there where means, Z=Heat capacity of calorimeter system, T=Rise in temperature M= Molecular Mass of substance W=Mass of substance taken.

Understand Bohr's Model of an atom

Understand Bohr's Model of an atom. Click on the link to Watch the VIDEO explanation: 
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Niels Bohr, postulated of module an atom on the basis of quantum theory. Each orbit is associated with definite energy and therefore called as energy shell or energy level. These energy levels are numbered starting from the nucleus as 1, 2, 3, 4 and so on or K, L, M, N. These integers are called the quantum no of the orbits. As long as electron remains in energy level it does not radiate energy. Electron gets promoted to higher energy level by absorbing a quantum of energy. Electron looses energy when an electron jumps from a higher energy level (E2) to a lower energy level (E1). In such a case energy E2-E1 is given out as radiation.

Understand the basic concepts of chemistry

Understand the basic concepts of chemistry. Click on the Link to Watch the VIDEO explanation: Watch Video

Law of chemical combinations. There are six laws that governs the combination of substances. Law of conservation of mass states that the total mass of the products equal to the total mass of reactants. Law of constant composition states that the elements combine in same proportion by mass. The law of multiple proportion states that the mass of one element combining with the other bear a simple whole number ratio to one another. The law of reciprocal proportion states that the ratio of combining masses of two elements `with the third one is same or whole no multiple of original ratio. Gay Lussac's law states that volume of reacting gasses bear a simple whole number ratio. Avogadro's law states that equal volume of all gasses contain equal number of molecules. Atoms and Molecules forms the basic building block of matter. An atom is the smallest part of an element. It also is the smallest particle of matter that can enter into chemical combination. A molecule is the smallest part of a substance that can have independent existence. It is formed when two or more atoms join together chemically. Atoms of elements are measured by their atomic mass. Their mass being miniscule, all atoms are compared on relative scale. It is 1/12th of the actual mass of Carbon 12 atom. When atomic mass of an atom is measured in gram it is called gram atomic mass. Molecules of substances are also measured by relative mass. It is defined as average relative mass of a molecule of a substance. When molecular mass is measured in gram it is called gram molecular mass. A chemical formula represents the composition and no of elements present in a molecule of a chemical compound. The molecular formula gives the actual no of atoms of each element present in one molecule of a compound. It also denotes molecular mass of a chemical substance. The empirical formula gives the simplest whole no ratio of atoms of different elements present in a molecule. Large molecules of ionic and network compounds are best described in this formula. The molecular formula will always be whole no ratio of empirical formula. A chemical equation symbolically represents a chemical reaction. According to the law of conservation of mass the changes in reactants and products must be balanced before and after reaction. Hit and trial method for simple equation and partial equation method for complex equation having many reactants and products.  The mole concept is the measure of concentration of substances in the chemistry. The mol unit is based on number of atom in exactly 12 gram of pure carbon 12.