Conversion of Galvanometer to Ammeter

A galvanometer is a device used to detect feeble electric currents in a circuit. It has a coil pivoted (or suspended) between concave pole faces of a strong laminated horse shoe magnet. When an electric current passes through the coil, it deflects. The deflection is proportional to the current passed. A galvanometer can detect only small currents. Thus, to measure large currents it is converted into an ammeter. It can be converted into an ammeter by connecting a low resistance called shunt resistance in parallel to the galvanometer. Value of resistance is so adjusted that most of the current passes…

Tests for Phenols

Phenols are compounds containing one or more hydroxyl group attached to an aromatic ring. The simplest phenol is carbolic acid having the formula C6H5OH. It is a white crystalline solid. Other example are o,m and p-cresols, catechol and resorcinol.   This video explains how to identify phenol using some simple tests.  

Homology and Analogy

The central idea of biological evolution is that all life on earth shares a common ancestry and some similarities have evolved in other ways. These are called homologies and analogies. Homology refers to the traits inherited by two different organisms from a common ancestry. Organs such as bat’s wing, wings of birds, seal’s flipper, forelimb of a horse, and human arm are homologous organs. Plants too have homologous structures like those seen in animals. The leave of some plants like the pitcher, venus fly trap, poinsettia and cactus have homologous structure. Analogy refers to the similarity in function of two…

Chemical Tests for Nitrate

Nitrates are compounds containing nitrate ion. Nitrate ion consisting of one central nitrogen atom surrounded by three oxygen atoms in trigonal planar arrangement. The nitrate ion carries a formal charge of -1. Nitrates are mainly produced for use as fertilizers in agriculture because of their high solubility and biodegradability. Common examples of inorganic nitrate salts are sodium nitrate, potassium nitrate, ammonium nitrate etc. Leafy green foods such as spinach and arugula are rich source of inorganic nitrate.   This video explains how to test the presence of nitrate ion in a given salt.  

Saponification : The process of Making Soap

Soaps and detergents are essential to personal and public health. They safely remove germs, soils and other contaminants and help us to stay healthy and make our surroundings more pleasant. Soaps are made from fats and oils or their fatty acids. Soaps are sodium or potassium salts of long chain fatty acids. When triglycerides in fat/oil react with aqueous NaOH or KOH, they are converted into soap and glycerol. This is called alkaline hydrolysis of esters. Since this reaction leads to the formation of soap, it is called the Saponification process.   This video explains the saponification reaction for preparation…

Detection of Halogens in an Organic Compound

There are many organic compounds containing halogens such as fluorine, chlorine, bromine, iodine etc and are called organohalogen compounds. Some commonly known examples are carbon tetrachloride, chlorofluorocarbons, DDT, iodomethane, bromobenzene etc. Upon fusion with sodium metal, the halogens in the organic compound is converted to ionic sodium halides, which can be extracted by boiling the fused mass with distilled water and is used for the detection of halides.   This video explains how to detect the presence of halogens in an organic compound.  

pH Determination

pH is defined as the negative logarithm(base 10) of the hydrogen ion concentration in moles per liter. Neutral solution has pH value 7. pH of acid solution is always less than 7 whereas that of alkaline solution is always more than 7.pH of pure water is 7. pH indicator is a chemical that has different colors in different media. Litmus solution and litmus paper are commonly used as an indicator. For example, blue litmus turns red in acidic medium, the red litmus turns blue in alkaline medium.   This video explains how to determine the pH of a sample by…

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.