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Ohm’s Law

Figure of Merit of a Galvanometer

A galvanometer is a device used to detect feeble electric currents in a circuit. It consists of a coil suspended between the poles of a powerful magnet. As current passes through the coil, it deflects. It can be detected from the deflection on galvanometer needle. The deflection is proportional to the current passed through it. Its working is based on the principle that a coil placed in a uniform magnetic field experiences a torque when an electric current is set up in it. The deflection of the coil is determined by a pointer attached to it, moving on the scale….

Chromatography

Chromatography is a separation technique used to separate the different components in a liquid mixture. It was introduced by a Russian Scientist Michael Tswet. Chromatography involves the sample being dissolved in a particular solvent called mobile phase. The mobile phase may be a gas or liquid. The mobile phase is then passed through another phase called stationary phase. The stationary phase may be a solid packed in a glass plate or a piece of chromatography paper. The various components of the mixture travel at different speed, causing them to separate.   This video explains how to separate a mixture of…

Inclined Plane

An inclined plane, is an even surface that is tilted at an angle. It helps reduce the force necessary to move an object by increasing the distance it must be moved. The inclined plane consists of a smooth plane hinged to a base so that it can be set at any desired angle. If a body of mass (say m) is placed over an inclined plane, that is inclined at an angle θ with the horizontal, its weight mg acts vertically downward. The component mg cosθ of the weight acts normally downward on the plane balances the upward normal reaction…

Test for Carbohydrate, Proteins and Fats

The food we eat is one of the necessary factors in our daily life that provides nutritional support for the human body. Food consists of both organic and inorganic substances. Carbohydrates, fats and proteins are the main organic substances present in the food, which provide energy. One of the main components of our daily diet is carbohydrates. This type of foods includes sugars, starch and fibres. They are composed of sugar molecules that contain carbon, hydrogen and oxygen. Proteins are large biological molecules made up of large number of amino acid units. Because of the complex nature of protein, our…

Simple Pendulum

An ideal simple pendulum consists of a heavy point mass (called bob) tied to one end of a perfectly inextensible, flexible and weightless string. In practice, we make it by tying a metallic spherical bob to a fine cotton stitching thread. When a pendulum swings through a small arc, its bob is undergoing simple harmonic motion. The force causing the bob to swing along its arc is greatest when its speed is least. The force is least when the speed of the bob is greatest.   This video explains how to carry out simple pendulum experiment and calculate the acceleration…

Melting Point of an Organic Compound

The melting point is an important physical property of a compound. The melting point can be used to identify a substance and as an indication of its purity. A pure crystalline compound usually possesses a sharp melting point and it melts completely over a narrow range of temperature of not more that 0.5 -1 °C. The presence of even small amount of impurities usually produces a depression in the freezing points and shows a marked increase in the width of the melting point range. The melting point range of greater than 5 °C indicates that the substance is impure. For…

Detection of Nitrogen in an Organic Compound

There are many organic compounds such as amines, amides, nitro compounds, urea etc contains nitrogen as one of the main elements. Nitrogen is covalently bonded to the organic compound. Upon fusion with sodium metal, the covalently bonded nitrogen is converted to ionic sodium cyanide, which can be extracted by boiling the fused mass with distilled water and is used for the detection of nitrogen.   This video explains how to detect the presence of nitrogen in an organic compound.  

Study of Osmosis

Osmosis is the process in which solvent molecules moves through a semipermeable membrane from a region of higher concentration to a region of lower concentration until the amount of fluid is equalised on both sides of the semipermeable membrane. The fluid that passes through the semipermeable membrane is known as the solvent, while the dissolved substance in the fluid is known as the solute. A solution that is separated from another solution by a semipermeable membrane can have three osmotic states: isotonic, hypotonic and hypertonic. In an isotonic solution is the pressure at both sides of the membrane the same….

Verification of Archimedes’ Principle

Archimedes principle states that: “When a body is immersed in a liquid, an upward thrust, equal to the weight of the liquid displaced, acts on it.” Thus, when a solid is fully immersed in a liquid, it loses weight which is equal to the weight of the liquid it displaces. The principle applies to both floating and submerged bodies and to all fluids. It explains not only the buoyancy of ships and other vessels in water but also the rise of a balloon in the air and the apparent loss of weight of objects underwater.   This video explains how…

Separation of Components from a Mixture of Red and Blue Inks by Paper Chromatography

Chromatography is one of the most important separation techniques extensively used to separate mixtures into their components. It was first employed by a Russian scientist Mikhail Tsvet. In the paper chromatographic technique, the mixture of substances is applied onto a Whatman filter paper strip called stationary phase. A pure solvent or a mixture of solvents is allowed to move slowly over the stationary phase. This moving phase is called mobile phase. When mobile phase is moved over the mixture on the stationary phase, the components of the mixture gets gradually separated from one another.   This video explains how to…

Boiling Point of an Organic Compound

The boiling point of organic compounds can give important information about their physical properties and structural characteristics. Boiling point helps identify and characterise a compound. A liquid boils when its vapour pressure is equal to the atmospheric pressure. Vapour pressure is determined by the kinetic energy of a molecule. The boiling point of a liquid varies with the surrounding atmospheric pressure. A liquid at a higher pressure has a higher boiling point than when that liquid is at lower atmospheric pressure. The boiling point (BP) of an organic molecule is related to the molecular weight of the molecule and the…

Centrifugation

Sometimes the solid particles in a liquid are very small and pass through a filter paper. For such particles the filtration technique cannot be used for separation. Such mixtures are separated by centrifugation. So centrifugation is the process of separation of insoluble materials from a liquid where normal filtration does not work well.   This video explains how to separate cream from milk.  

Study of Plasmolysis

Plasmolysis is the process of shrinkage or contraction of the protoplasm of a plant cell as a result of loss of water from the cell. Plasmolysis is one of the results of osmosis and occurs very rarely in nature, but it happens in some extreme conditions. We can induce plasmolysis in the laboratory by immersing living cell in a strong salt solution or sugar solution to lose water from the cell. Normally people use Rheo or Tradescantia plant epidermal cell for experiment because they have coloured cell sap which can be clearly visible.   This video explains how to demonstrate…

Reaction Between Sodium Sulphate and Barium Chloride Solution

When barium chloride combines with sodium sulphate in the form of their aqueous solutions, a white precipitate of barium sulphate is formed which is insoluble in water. The reaction also creates sodium chloride, which remains dissolved in water and so cannot be seen. Here, the products formed are entirely different from the reactants in chemical composition and chemical properties. So this reaction is a chemical change.   This video explains the chemical change occurs during the reaction between sodium sulphate and barium chloride.  

Sonometer

The sonometer itself consists of a wire stretched between two supports or bridges on a wooden sounding box. The tension of the string may be varied either by a screw or by hanging weights on one end of it. The length of the vibrating wire can be changed using a small wooden support that can be moved along under the wire.   The purpose of the sounding box is to make a larger mass of air vibrate and so amplify the very small sounds produced by the vibrating string itself. If a string which is stretched between two fixed points…

Chemical Tests for Chloride

Chlorides are salts of chlorine gas containing chloride ion. Chloride ion is formed when the element chlorine gains an electron. The most commonly known chloride salt is sodium chloride which is used to preserve food. Another important example of chloride is calcium chloride, used as a desiccant in laboratory desiccators to maintain a dry environment.   This video explains how to test the presence of chloride ion in a given salt.  

Preparation of Lassaigne’s Extract

In order to detect the elements in organic compounds, they have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal. The ionic compounds formed during the fusion are extracted in aqueous solution and can be detected by simple chemical tests. The extract is called sodium fusion extract or Lassaigne’s extract.   This video explains how to prepare Lassaigne’s extract of the given organic compound.  

Heating of Copper Sulphate

Copper sulphate pentahydrate contain 5 moles of water per one mole of copper (II) sulphate. Its formula is written as CuSO4.5H2O and has blue colour due to water of hydration. It can be converted into anhydrous copper sulphate when heated strongly. When heated, it loses two water molecules at ~63°C followed by two more at ~109°C and the final water molecule at ~200°C and turns to white coloured anhydrous copper sulphate. This above process can be reversed. When water is added to white coloured anhydrous copper sulphate, its colour changes to blue, indicating that the blue coloured copper sulphate pentahydrate…

Detection of Albumin in Urine

Albumin is normally found in the blood and filtered by the kidneys. When the kidneys work normal, there may be a very small amount of albumin in the urine. But when the kidneys are damaged, abnormal amounts of albumin leak into the urine. This is called albuminuria.   This video explains how to detect the presence of albumin in urine.