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.
Stomata are minute pores found on the epidermis of leaves and young shoots of plants that are used to control exchange of gases. The pore is surrounded by a pair of specialised cells called the guard cells that are responsible in regulating the size of the opening. Distribution of stomata varies between monocots and dicots, between plant species, and between the underside and top side of the leaves on a plant. Stomata are found more on plant surfaces thriving under higher light, lower atmospheric carbon dioxide concentrations and in moist environments. Usually the lower surface of a dicot leaf has…
The screw gauge is an instrument used for measuring accurately the diameter of a thin wire or the thickness of a sheet of metal. It consists of a U-shaped frame fitted with a screwed spindle which is attached to a thimble. The pitch of the screw is the distance moved by the spindle per revolution. To find this, the distance advanced by the head scale over the pitch scale for a definite number of complete rotation of the screw is determined. This video explains how to find the volume of a wire and an irregular lamina along with the…
The metre bridge is operates under Wheatstone’s principle. Here, four resistors P, Q, R, and S are connected to form the network ABCD. The terminals A and C are connected to a battery, and the terminals C and D are connected to a galvanometer through keys K1 and K2 respectively. In the balancing condition, there is no deflection on the galvanometer. Then, P/Q = R/S. This video explains how to find the resistance of a given wire using a metre bridge and hence determine the specific resistance of its materials.
The oxidation and reduction reactions in aqueous solutions involve the transfer of electrons from one species to another. In the oxidation of a substance electron(s) is (are) transferred from the species and in reduction, electron(s) is (are) gained by the species. Oxidation and reduction reactions occur simultaneously. A reaction, which involves simultaneous oxidation and reduction, is called a redox reaction. The titrations involving redox reaction are called redox titrations. In Redox titrations involving potassium permanganate, it acts as a powerful oxidising agent. This video explains how to determine the strength of potassium permanganate solution by titrating it against a…
The type of reproduction that takes place without the process of gamete (sex cell) formation is called asexual reproduction. Asexual reproduction is the primary form of reproduction for single-celled organisms such as the archaea, bacteria, and protists. Many plants and fungi reproduce asexually as well. Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only. The offspring will be the exact genetic copies of the parent. Binary fission and budding are two common method of asexual reproduction. Binary fission is found in unicellular organisms like Amoeba, Paramaecium…
The cell is possibly the most important concept in biology since it is the basic unit of life. Every living organism is made up of cells (or just one in the case of bacteria). All the animals, trees and plants are made up of cells that share many similar characteristics. An onion is a multicellular (consisting of many cells) plant organism.As in all plant cells, the cell of an onion peel consists of a cell wall, cell membrane, cytoplasm, nucleus and a large vacuole. The presence of a cell wall and a large vacuole are indicators that help identify…
The modern Vernier caliper was invented by Joseph R. Brown in 1851. It was the first practical tool for exact measurements that could be sold at an affordable price to ordinary machinists. The Vernier Caliper consists of a main scale fitted with a jaw at one end. Another jaw, containing the vernier scale, moves over the main scale. When the two jaws are in contact, the zero of the main scale and the zero of the Vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error. This video explains…
Titration is a common laboratory method of qualitative chemical analysis that can be used to determine the unknown concentration of a solution (analyte). The basis of this process is the reaction between the analyte and a solution of unknown concentration (standard solution). The titration based on oxidation and reduction reaction between the titrant and analyte is called Redox titration. Oxidation is the process of the addition of oxygen or removal of hydrogen/electron and reduction involves the process of addition of hydrogen/electrons or removal of oxygen. In redox systems, the titration method can be adopted to determine the strength of a…
Sphero Meters are small precision instruments for measuring the radius of curvature of spherical surfaces. They can also be used to measure the thickness of a thin plate. A spherometer works on the principle of the micrometer screw. Spherometer consists of a metallic tripod framework supported on three fixed legs of equal lengths. A screw passes through the centre of the tripod frame, parallel to the three legs. A large circular disc graduated with 100 equal parts is attached to the top of the screw. A small vertical scale known as the Pitch scale (P) with the scale reading divided…
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