Surface tension is the property of a liquid, by virtue of which its free surface at rest behaves like an elastic skin or a stretched rubber membrane, with a tendency to contract so as to occupy minimum surface area. This property is caused by cohesion of molecules and is responsible for much of the behaviors of liquids. Surface tension has been well- explained by the molecular theory of matter. According to this theory, cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. The molecules well inside the liquid are attracted equally in all directions by the…
Potash alum is a double salt of potassium sulphate and aluminium sulphate. It has the formula K2SO4.Al2(SO4)3.24H2O. It is prepared by dissolving an equimolar mixture of hydrated aluminium sulphate and potassium sulphate in minimum amount of water containing a little of sulphuric acid and subjecting the resulting solution to crystallization, when octahedral crystals of potash alum separate out. This video explains how to prepare a pure sample of potash alum.
Aldehydes are organic compounds containing formyl functional group, in which the carbonyl carbon is attached to a hydrogen atom and an R group. The R group may be an alkyl or aryl group. Aldehydes are formed by replacing hydrogen atom of a hydrocarbon by the formyl group. The flavours of Almond, vanilla beans and cinnamon are due to the presence of aldehyeds. This video explains how to identify aldehydes using some simple tests.
All matter has mass and volume. These are the physical properties of matter and may vary with different objects. The amount of matter contained in an object is called its mass and the amount of space occupied by the object is called its volume. So, the mass of a unit volume of a substance is called its density. This video explains how to determine the density of a solid (which is denser than water) by using a spring balance and a measuring cylinder.
Zinc is more reactive than hydrogen and it displaces hydrogen from dilute acids. Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas is evolved. Since the products zinc sulphate and hydrogen gas are entirely different in chemical composition and chemical properties from the reactants, the reaction is a chemical change. This video explains the chemical change occurs during the reaction of zinc with dil. sulphuric acid.
Carboxylic acids are organic compounds containing carboxyl functional group. It is of two types aliphatic and aromatic. Formic acid and acetic acid are the simplest aliphatic acid and benzoic acid is the simplest aromatic acid. The fruits such as lemon, grape, orange and green apple also contain carboxylic acid. This video explains how to identify carboxylic acids using some simple tests.
Sugar (glucose) is usually present in the urine at very low levels or not at all. Abnormally high amounts of sugar in the urine, known as glycosuria, are usually the result of high blood sugar levels. High blood sugar usually occurs in diabetes, especially when untreated. When the blood sugar is high, there is too much sugar in the fluid leaving the kidney to be reabsorbed, so some sugar passes into the urine.Sugar in the urine can be detected in the laboratory or is easy to detect at home with a urine dipstick test. This video explains how to…
Benzoic acid is a colourless crystalline solid. It is highly soluble in hot water, but poorly soluble in cold water. It can be recrystallized by dissolving it in hot water. The hot solution obtained is filtered and cooled. Upon cooling, opaque white crystals of benzoic acid crystallise. This video explains how to prepare pure crystals of benzoic acid form an impure sample through crystallization.
A beam balance is a device used for the determination of the mass of a body under gravitation. It consists of a beam supported at the center by an agate knife edge resting on a support moving inside a vertical pillar. The beam carries a light pointer which moves over a scale. There are two stirrups at the ends of the beam which carries two scale pans of equal masses along with adjusting nuts. These can be adjusted to make the pointer to oscillate within the scale when the balance is raised. The balance is mounted on a platform provided…
Sulphur is a non – metallic chemical element with the symbol ‘S’. It is present in many organic compounds like thiol, carbon disulphide etc. The antibiotics penicillin and the artificial sweetener saccharin etc are also sulphur containing organic compounds. Upon fusion with sodium metal, the sulphur atom in the organic compound is converted to ionic sodium sulphide, which can be extracted by boiling the fused mass with distilled water and is used for the detection of sulphur. This video explains how to detect the presence of sulphur in an organic compound.
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…
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.
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…
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.
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…
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 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…
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….