7th Class

   Climate and Weather   Climate has a great effect on all the living organisms. Record of weather at a particular place is preserved for long period of time (30 years), which is known as the climate of that place. If observation of temperature of the particular place is high, we say that the climate is hot and if low temperature is recorded then climate is cold. There are four types of climate in the world. These are polar climate, temperate climate, tropical climate and desert climate. Polar region receives less amount of solar energy from the Sun, therefore, climate is cold in the polar region. Look at the following picture of the polar region   The weather in the temperate climate is neither too hot in summer and nor too cold in winter. Weather in the more...

   Adaptation of Animals in Different Climate The presence of specific body features, which enable an animal or a plant to live in a particular habitat, is called adaptation. Migration of the birds protects them from extreme cold and hot climates. Siberian crane is a migratory birds, which come every year in India, during winter. Look at the following picture of penguins and polar bears                                        Fig. (1) Penguins                                                                      Fig (2) Polar bear     Penguins cannot fly but they can swim by their flippers. Penguins live in the extreme cold climate of south Polar Region. Thick skin of penguins and the layer of fat under their skin protect them from extreme cold weather. Penguins huddle together to keep themselves warm. They eat fishes. Polar bear more...

     Pollution   There are various polluting elements which are causing pollution in our environment. The most common causes of the land pollution is the dumping of waste materials. Polythene, plastic metals, glass etc. pollute the soil. The use of pesticides is also a major cause of soil pollution. Pesticides are the chemicals used for the protection of crops from harmful bacteria. Pesticides enter in the soil thereby polluting it. Fertilizers are also made from chemicals (acid and alkalis). The excess presence of chemicals in the soil is resulting in soil pollution. Acid rain also cusses the soil pollution. Acid rain occurs due to the air pollution.   Look at the following picture of soil pollution               more...

      Salt and its Types   Salt is formed by the reaction of an acid with a base. Sodium chloride is formed by hydrochloric acid and sodium hydroxide base. The salt is prepared by the reaction of strong acid with weak acid. The salts of hydrochloric acid are called hydroxide and the salts of sulphuric acid are called sulphate. The salts of nitric acid are called nitrate. The salts of carbonic acid are called carbonates and the salts of acetic acid are called acetates. There are three kinds of salt that is, natural salt, acidic salt, and basic salt. The salt, which form a neutral solution on dissolving into water are called natural salt. I.e. sodium chloride  and sodium sulphate. Natural salt does not have effect on litmus paper and the colour of litmus more...

     Uses of Acid and Base   Acids are used in the laboratory and industries for various purposes. Nitric acid is used to increase the fertility of the agriculture land, like, ammonium nitrate, calcium ammonium nitrate, etc. Nitric acid is also used in explosive. It is used for the washing of precious metal like, gold and silver. Sulphuric acid acts as a reactance in the manufacturing of fertilizers, like ammonium sulphate, super phosphate. It is used in refineries, car batteries, and in chemical reactions. Hydrochloric acid is used for bleaching in the textile industries, and it is also used for the purification of salt. Basic solutions are also very useful for us. Antacid is used for relaxation from the acidity. Antacid is a basic solution and known as milk of magnesia or magnesium hydroxide. A bitter taste is the characteristics of the all bases. more...

     Method of Testing Acid and Base   The testing of acid is done by indicators, i.e. litmus.              Testing of Add It requires two litmus, two beakers and the solution of acid and base. The nature of substance, whether it is acidic or basic is obtained from the colour of litmus. The blue color of litmus turns into red, if the solution ,s acidic. The red color of litmus turns into blue, if the solution is basic.   Look at the following picture of testing of Acid Blue litmus turns to red                              Red litmus turns to blue                                                                    All acids are aqueous more...

       Concentrated and Diluted Acid   The substance, which has hundred percent of acid is called concentrated acid.  It completely dissolves in water and furnish ions. The concentrated acid is also called strong acid. The acid, which has lower percent of acid is called diluted or weak acid. Dilute acid is not a pure form of acid, during the chemical reaction its performance is slower than the concentrated acid. It does not dissolve completely in water or furnish ions. In the following chemical reaction, carbon dioxide reacts with water and gives hydro carbonic acid. This is the weak and diluted acid.   Acids can be categorized into three main types, natural acids, mineral acid and organic acid. Natural acid is obtained from plants. The sources of citric acids are lemon and orange. more...

       Indicators   Indicators are used to indicate the nature of a substance. Chemical compounds have been categorized into three groups, that is, acid, base and salt, according to their nature. The substance whose nature is acidic (sour in test), called acid and whose nature is basic (bitter in test) is called base. Litmus is the natural indicator and used for the testing of the solution. Litmus paper turns blue to red if the solution is acid, and it turns red to blue if the solution is base. Litmus paper is widely used in the chemical laboratory.   Look at the following picture of Litmus                                                                           Acid                                     more...

       Thermo Flask   Look at the given picture   1- Screw on top 2 - Outer cover is of plastic or steel 3 - Outer layer is of glass or steel coated 4 - Vacuum 5- Inner layer is of glass or steel coated 6 - Support 7 - Additional insulation reduces heat loss   Thermo flask is used for keeping a liquid in its original form. A glass of hot water in a thermo flask remains hot long time due to it’s built up. A screw part on its top is used for inlet or outlet. It also protects liquid from lay down. Heat, produced by the hot liquid does not radiate. External heat or cold does not absorb by the liquid. Plastic and lead inside the flax is the poor conductor of more...

     Absorption of Radiated Heat   Every object absorbs more or less heat from atmosphere or from other heat producing sources. If we put anything in the sunlight, after some time it gets heated. The amount of heat to be absorbed by a body depends on its heat absorption capacity. It also depends on the amount of heat produced by the body. On the surface of the Earth, various colors are available. The heat absorption capacity of every object depends on its color also. Black color absorbs more heat than oth.er colors. White color reflects more heat than others. The objects having dark color absorb more radiated heat than the objects of light color.   In the figure below, there are two coffee cans taken for an experiment to show the absorption of radiant energy. Thermometers inside the coffee are used for the measurement more...