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…
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…
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…
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.
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…
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.
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…
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.
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.
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…
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.
Paper chromatography is an analytical method, used to separate coloured substances, especially pigments. In paper chromatography, the sample is distributed between a stationary phase and a mobile phase. The stationary phase is usually a piece of high quality filter paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. When mobile phase is moved over the sample on the stationary phase, the components of the sample gets gradually separated from one another. This video explains how to separate the pigments from the extract of spinach leaves by paper chromatography.
Fractional distillation is used for the separation of a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K. The apparatus for fractional distillation is similar to that of simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser. This video explains how to separate a mixture of ethanol and water by fractional distillation.
Young’s modulus, also known as the elastic modulus, is a measure of the stiffness of a solid material. It is a mechanical property of linear elastic solid materials. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material. Young’s modulus is named after the 19th-century British scientist Thomas Young. A solid material will deform when a load is applied to it. If it returns to its original shape after the load is removed, this is called elastic deformation. In the range where the ratio between load and deformation remains constant, the stress-strain curve…
Crude copper sulfate is a mixture of copper sulfate with various impurities that may include copper carbonate, copper oxides, and other copper compounds. To crystallise copper sulphate, dissolve it in water and add a small quantity of dilute sulphuric acid to prevent the hydrolysis of copper sulphte. The impurities left behind in the solution are removed by filtration. The filtrate is concentrated to the crystallisation point and then cooled. On cooling, transparent blue crystals of copper sulphate separate. The copper sulphate crystal formed has triclinic shape. This video explains how to prepare the crystals of pure copper sulphate form…
Dicot stems have a circular arrangement of vascular tissues, whereas the stems of monocots have vascular-tissue bundles scattered throughout. In monocots the vascular bundles also tend to be toward the outside of the stem. Dicot vascular tissue forms a cylinder near the center of the stem. Monocot roots, interestingly, have their vascular bundles arranged in a ring. Dicot roots have their xylem in the center of the root and phloem outside the xylem. A carrot is an example of a dicot root. This video explains how to prepare temporary stained glycerine mounts of transverse sections of the stem and…
When one body makes an attempt to slide over another body, an opposing force called the force of friction arises as a reaction to the applied force, and acts in the opposite direction. Static friction is the type of friction that exists when two objects touch each other at rest. It has a limiting value called limiting friction, which is equal to the least force required to move the body from rest. When the external force F is increased, a stage comes when the body is just at the verge of moving. At this stage, the force of friction is…
Flowering plants, also known as Angiosperms, are the most diverse group of land plants in the world, with at least 2,60,000 living species classified into 453 families. The flowering plants were divided onto eight major groups, the largest number of species belonging to monocots and dicots. Monocot and dicot plants have specific characteristics. We identify plants by looking at their external characteristics such as seeds, roots, leaves, flowers, pollen, stems and vascular bundles. Based on the differences, they are placed in one of these two groups. This video explains how to study the external features of Monocot and Dicot…
Stoma is a pore found in the epidermis of leaves, stems and all other plant parts found above the ground. Stomata are thus named because they permit the exchange of gases between the atmosphere and the inside of the leaf. Stomata are found on either both sides or on just one side of the leaf. The distribution of stomata varies in different plants. There are more stomata on plant surfaces in conditions like lower atmospheric carbon dioxide concentrations, moist environments and higher light. In dicot plants the number of stomata is greater on the lower surface than on the upper…
If two vectors acting simultaneously on a particle are represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point, then their resultant is completely represented in magnitude and direction by the diagonal of that parallelogram drawn from that point. This video explains how to find the weight of a given body using the Parallelogram Law of Vectors.