Shikshakendra

  ~CHAPTER AT A GLANCE ▪︎ 1).Metals : metals show metallic  lustre, are generally hard,malleable   and ductile. They are good conductors of heat and electricity.    2).Metals are sonorous : metals produce a sound when they strike a hard surface. We Express it by saying that metals are sonorous. That it why school bells are made of  metals.  3). Non metals : substances like carbon, sulphur and iodine are non metals. They are either solid or gas with the exception of bromine which is liquid.  4).Exceptions :  (i) Metals in general have high melting points. But mercury, gallium and Celsium have low melting points and are liquids at room temperature. (ii) Iodine, a non-metal, show lustre. (iii) Diamond, an allotrope of carbon, is the hardest natural substance known. Graphite, another allotrope of carbon, is a conductor of electricity. 

  CHAPTER AT A GLANCE  1. An optical prism has two triangular bases and three rectangular lateral surfaces, which are inclined to each other. Angle between it's two lateral faces is called the angle of prism.   Whenever, refraction of light takes place through a prism, the emergent ray is called the angle of deviation D.   2. When a beam of white light passes through a glass prism, it splits up into its constituent seven colours. These seven colours are remembered by the acronym 'VIBGYOR'. The splitting of white light into its component colours is called 'dispersion of light's. The band of the coloured components formed due to dispersion is called 'spectrum'.      Dispersion is on account of different amount of deviations for light of different colours. Red coloured ray bends the least but violet ray bends the most. Thus, spectrum is formed.  Seven colours of VIBGYOR can be recombined so as to form white light . 3. Rainbow is a natural spectr...

  ~ Some Terms Related To Spherical Mirrors :  Following are some of the important terms related to spherical mirrors :  i) Pole of a mirror : The centre of the reflecting curved surface of a spherical mirror is called the pole of the mirror. It is usually represented by letter p. The point p in fig. 4.14 (a) and (b), represents the pole of a concave mirror and a convex mirror. It should be noted that the pole of a spherical mirror is also called vertex of the mirror.    ii) Centre of curvature : It is the centre of hollow sphere of glass of which the spherical mirror forms a part. It is represented by the letter C.  It should be noted that the centre of curvature is not a part of the mirror. It lies outside its reflecting surface. The centre of curvature of a concave mirror lies in front of it [see Fig. 414 (a)]. However, it lies behind the mirror in case of a convex mirror [see Fig. 4. 14 (b)]. iii) Radius of curvature: The radius of the sphere of which t...

2.   Phenolphthalein: Phenolphthalien is a colourless substance. It is a synthetic indicator which is prepared in the laboratory or manufactured in the industry. In acidic solution, it remains colourless . However, adding a drop of phenolphthalein to a basic solution, turns the solution pink .  3. Methyl orange : it is also a synthetic indicator manufactured in industry or prepared in the laboratory. Methyl orange is an orange colour dye. When a drop of methyl orange is added to an acidic solution, it turns the solution red . On adding a drop of methyl orange to a basic solution, the solution turns yellow .   The colour changes of phenolphthalein and methyl orange in the acidic and basic (alkaline) solutions are given in the table 2.4 :  Let as discussed an experiment to understand the role of indicators in the identification of acid and basic solutions. EXPERIMENT :   To test acids and bases in the laboratory using change acid-base indicators. Collect the ...

~INDICATORS TO TEST ACIDS AND BASES  Some substances change their colour (or odour) on addition of an aqueous solution of an acid or base. These substances are called (acid-base indicators) . Using these substances, it is possible to identify acids and bases. Acid-base indicators are generally coloured organic substances. Well known three indicators are Litmus, phenolphthalein and methyl orange. Litmus is a natural indicator ( i.e., found in nature in plants) while phenolphthalein and methyl orange are synthetic indicators ( i.e., synthesised in the laboratory). Let us discuss them, one by one. 1) Litmus : Litmus is a natural indicator. It is extracted from lichen  a plant belonging to the division Thallophyta. The colour of Litmus solution is purple and it is neither acidic nor basic. It is neutral. In the acidic solution, it turns red while in the basic solution, it turns blue. Most often, instead of using the litmus solution as such, two types of Litmus solutions are used k...

  (ii) Mineral Acids :  The acids formed from minerals present in the earth's crust are known as mineral acids. Nitric acid was the first mineral acid. Later on, sulphuric acid and hydrochloric acid were discovered. These mineral acids much stronger than ethanoic acid and allow more chemical reactions to take place. Many chemical discoveries are based on the use of these acids.  In everyday life, we used a number of acids. Hydrochloric acid is used in cleaning kitchen sinks and sanitary wares. It is worth to note that hydrochloric acid is produced in our stomach also. Sulphuric acid is used in batteries of inverters, cars, buses, trucks, etc. Nitric acid is used by goldsmiths for cleaning gold and silver ornaments. Given in table 2.2 are the important mineral acids with their chemical formulae. From the above discussion, we find that one element is common to all the acids, which is hydrogen. Thus, we can say that presence of hydrogen is essential for a substance to act as...

~ INTRODUCTION  There are a large number of compounds in which some are organic (obtained from animals and plants) and other are inorganic (obtained from Minerals and rocks). These compounds and present in the food materials and in a number of other materials as well which we use in our everyday. On the basis of their chemical properties (such as test, order, etc.) all the compounds can be classified into the following three categories:   i)Acids, ii)Bases, and iii)Salts. In this chapter, we shall study all the three types of compounds ( i. e., acids, bases and salts) in more details. Also, we shall discuss the common characteristics of acids and bases, and their chemical nature.  ~ ACIDS  The term acid was originally used to describe any substance which had a sour taste.  The world acid has been derived from the Latin word acids, which means sour . Many fruits are sour because they contain acid. A few more examples of acidic substances  used in everyday ...