Current Affairs 10th Class

Chemical Reactions and Acids, Bases and Salts   Chemical Reactions During a chemical reaction, new substances with new properties are formed chemical changes are involved during a chemical reaction. During a chemical reaction, rearrangement of reacting substances takes place to form new substances, which have different properties than the original one. In a chemical reaction, substances are divided into reactants and products. Recants are the substances that take part in a chemical reaction whereas products are the substances that are formed as a result of chemical reaction.   Endothermic and Exothermic Processes In all the chemical reactions transformation or change in energy is involved. On the basis of change in energy all the reactions are divided into two parts that are endothermic and exothermic reactions. The reaction in which heat is absorbed is call endothermic reaction. The reaction in which energy is given out in the surroundings is called exothermic reaction. Photosynthesis is an example of an endothermic reaction. In process of photosynthesis, plants by utilising the energy of the sun convert carbon dioxide water and into glucose and oxygen. \[\underset{(Carbon\,\,dioxide)}{\mathop{6C{{O}_{2}}+6{{H}_{2}}O}}\,\xrightarrow[Chlorophyll]{Light}\underset{(Carbohydrate)}{\mathop{{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{O}_{2}}}}\,\]   Sodium and chlorine are mixed together to yield table salt is an example of exothermic reaction. 411 kJ of energy is produced in this reaction. \[Na+0.5C{{l}_{2}}(s)\xrightarrow{{}}NaCl(s)+411\,\,kJ\]   Chemical Equation A chemical equation is a way of writing or describing chemical reactions. It tells us that what happens when a chemical reaction takes place. It consists of information about reactants, products the formulas of the reactants and products, the states of the reactants and products such as solid, liquid, gas and the amount of each substance.   Balancing the Equation To get the same number of atoms of every element on each side of the equation, apply the law of conservation of mass. Now balance an element that appears only once in reactant and product. After balancing one element, proceed further to balance the next and continue balancing until all the elements are balanced. Now you need to balance chemical formulas by placing coefficients in front of them. Do not add subscripts because this will change the formulas.   Types of Chemical Reactions             All the chemical reactions are divided into six categories. These six categories are as follows:   Combination Reaction When two or more elements or compounds combine to form a compound, then combination reaction takes place. They are mostly exothermic.             The combination of iron and sulphur to form iron sulphide is an example of combination reaction:             \[8Fe+{{S}_{8}}\xrightarrow{{}}8FeS\]             (Iron) (Sulphur)  (Iron sulphide)   Decomposition Reaction When a complex compound breaks down to make simple molecule, decomposition reaction takes place. They are always endothermic. The electrolysis of water to make oxygen and hydrogen gas is an example of decomposition reaction: \[2{{H}_{2}}O\xrightarrow{{}}2{{H}_{2}}+{{O}_{2}}\] (Water)   (Hydrogen) (Oxygen)   Single Displacement Reaction When in a reaction an atom or a group of atoms present in a molecule is displaced by another atom, is known as displacement reaction. The displacement more...

Metals and Non - metals   There are about 118 elements, from which 92 are naturally occurring. Metals and non-metals are characterized by their physical and chemical properties.   Characteristics of Metals  

• Metals have tendency to lose electrons.
• Metals are strong and tough.
• Metals have high melting and boiling point.
• Most of the metals are malleable or can be changed into thin sheets. For example, aluminium can be drawn into thin sheets.
• Metals are ductile or can be drawn out into thin wires. For example, copper can be drawn into wire.
• Metals are good conductor of electricity and heat.
• Metals are solids at room temp except mercury, which is a liquid.
• Metals are lustrous.
• Metals tend to have low ionization energies. In other words they gets oxidized when they undergo chemical reactions.
• Metals from compounds with non – metals that are ionic in nature.
• Most metal oxides are basic oxides. They dissolve in water to form metal hydroxides.

\[Metal\,Oxide+water\to metal\,hydroxide\] \[N{{a}_{2}}O(s)+{{H}_{2}}O(l)\to 2NaOH(aq)\] \[CaO(s)+{{H}_{2}}O(l)\to Ca{{(OH)}_{2}}(aq)\]

• Metal oxides exhibit their basic chemical nature by reacting with acids to form salts ice water:

\[Metal\,oxide+acid\to salt+water\] \[MgO(s)+HCl(aq)\to MgC{{l}_{2}}(aq)+{{H}_{2}}O(l)\] \[NiO(s)+{{H}_{2}}S{{O}_{4}}(aq)\to NiS{{O}_{4}}(aq)+{{H}_{2}}O(l)\]   Characteristics of Non Metals  

• Non- metals have tendency to gain electrons.
• Non- metals are brittle. They are neither malleable nor ductile.
• Non -metals are non- lustrous.
• Non -metals are poor conductors of heat and electricity.
• Non- metals have melting point lower than metals.
• Non- metals, gain electrons or reacting with metals to attain noble gas electrons configuration and become anions.
• Most non -metal oxides are acidic oxides. These acidic oxides dissolve in water to form acids.

\[Non\,metal\,oxide+water\to acid\] \[C{{O}_{2}}(g)+{{H}_{2}}O(l)\to {{H}_{2}}C{{O}_{2}}(aq)\] (carbonic acid)

• Non -metal oxides can combine with bases to form salt and water.

  Metalloids Metalloids have properties intermediate between the metals and non- metals. Silicon for example appears lustrous, but is neither malleable nor ductile but is brittle which the characteristic of some non -metals. Metalloids are also useful in the semi- conductor industry.

Carbon and Its Compounds   Carbon the 6th element in the periodic table. We all are familiar with the black js forms of carbon which are coal, charcoal and soot. Most of the things such as food, medicines, clothes, paper contain carbon. All living organisms contain carbon. Carbon is also present in small amount in the earth's crust and in the atmosphere. Carbon is a tetravalent element. It can occur either in free state as diamonds, graphite buck minster fullerene or in the combined state such as carbon dioxide, carbonates, coal Petroleum and organic compounds like carbohydrates, fats and proteins, etc. Carbon has large number of organic compounds as it can form long chains of its own atoms. This is a unique characteristic that carbon element have among all other elements. This Property to form long chains of its own atoms is called catenation. Important Structural elements of life are formed from long chains of carbon atoms that exist in different molecular forms. And another reason for the large number of organic compounds of carbon is that the valency of carbon is 4 (which is quite large).   Hydrocarbons Carbon forms large number of compounds with hydrogen element called hydrocarbons. The hydrocarbons are categorized into two categories, namely saturated hydrocarbons and unsaturated hydrocarbons.   Saturated Hydrocarbons Saturated hydrocarbons are the compounds of carbon and hydrogen in which carbon atoms contain only one carbon – carbon bond. The bond between carb on and hydrogen is also single covalent bond. They are called saturated compounds because all the four bonds of carbon are fully utilized and no more hydrogen or other atoms can attach to is. Saturated hydrocarbons can undergo only substitution reactions. Saturated hydrocarbons are also called alkanes. The general formula of saturated hydrocarbons or alkanes is\[({{C}_{n}}{{H}_{2n+2}})\]where n is the number of carbon atoms.   Unsaturated Hydrocarbons Unsaturated hydrocarbons are the compounds of carbon and hydrogen that contain one double covalent bond between carbon atoms or a triple covalent bond between carbon atoms. In these compounds all the bonds of carbon are not fully utilised by hydrogen atoms and thus more hydrogen atoms can be attached. These compounds can undergo addition reactions to add hydrogen because they have two or more hydrogen atoms less than the saturated hydrocarbons or alkane\[({{C}_{n}}{{H}_{2n+2}})\]. Unsaturated hydrocarbons containing double bond are called alkenes\[({{C}_{n}}{{H}_{2n}})\] and those that contain triple bond are called alkynes\[({{C}_{n}}{{H}_{2n-2}})\]. The carbon atom chain can be a linear or branched chain which is an open chain.   The carbon atom chain can be cyclic or closed rings, sheets and even three-dimensional     When there are more than three carbon atoms, compounds can be branched. The branched chains provide different structure to the parent alkane and are named differently. For example, in pentane\[({{C}_{5}}{{H}_{12}})\]there exist a straight chain and branched chain called Iso-pentane. Carbon can thus form more...

Periodic Classification of Elements   At present about 115 elements are known. All the elements are divided into groups such that the elements in the same group have similar properties. The periodic classification of elements helps in systematic study of elements and makes it easy to understand the properties of elements.   Dobereiners’s Triads Johann Wolfgang Dobereiner, a German scientist, was the first to classify elements. He grouped the elements with similar chemical properties into groups of three called ‘Triads’. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was equal to the approximate arithmetic mean of the atomic masses of the other two elements of the triad. For example, Li, Na, K and Cl, Br, I.   Limitations of Triad Classification  

• Large number of similar elements could not be grouped into triads. For example, iron, manganese, nickel, cobalt, zinc and copper have similar properties but cannot be placed in the triads.
• It was possible that quite dissimilar elements could be grouped into triads.
• Dobereiner failed to arrange all the elements known at that time in the form of triads.

  Newlands’ Octaves John Alexander Reina Newland arranged many of the known elements in the increasing order their atomic masses. He noticed that every eighth element was similar in properties to the first element. The eighth element after lithium is sodium. It is similar to lithium in many of its chemical properties. Similarly, the eighth element after sodium is potassium, whose properties are similar to sodium. The eighth element from fluorine is chlorine both of which are similar in their properties. The eighth element from nitrogen is phosphorus and both these elements are similar in properties. Based on this observation, Newland stated his law of octaves. According to this law 'when elements are arranged in increasing order of their atomic mass, the eighth elements resembles the first in physical and chemical properties'. This repetition of properties of elements gave rise to a new term called periodicity. Periodicity is the recurrence of characteristic properties of elements arranged in a table, at regular intervals of a period   Advantages of the Law of Octaves  

• The law of octaves was the first logical attempt to classify elements on the basis of atomic weights.
• Periodicity of elements was recognised for the first time.

  Mendeleev's Periodic Law Later, Mendeleev arranged the sixty-three elements known at that time in the increasing order of the atomic masses, in the form of a table called the Periodic Table. Mendeleev's periodic table further classified the elements by arranging the elements with similar properties together and separating the elements with dissimilar properties from one another. Mendeleev stated the law of chemical periodicity as: "The physical and chemical properties of elements are periodic functions of their atomic masses." Mendeleev's periodic table contains eight vertical columns of elements called 'groups' and seven horizontal rows called 'periods. more...

Life Processes   Life Processes All the living organisms on this planet perform some basic functions to maintain their life on the earth. These functions are called life processes. It includes nutrition, respiration, excretion, control and coordination, growth, movement and reproduction. Food is the main source that provides energy to all the living things to carry out various life processes.   Nutrition Nutrition is the process of intake of nutrients by an organism and the utilisation of these nutrients. It is a substance that is obtained by an organism from its surrounding and used as a source of energy. Our body needs different types of nutrients in right amount. They are carbohydrates, fats, proteins, vitamins, minerals and roughage.   Mode of Nutrition Different organisms obtained their food in different ways. Thus the mode of nutrition among organisms is different. The following are the two modes of nutrition among the Organisms.  

• Autotrophic mode of nutrition: In this mode of nutrition, an organism makes its own food with the help of carbon dioxide, water and sunlight. Green plants have this mode of nutrition. Green plants make their own food by the process of photosynthesis in the presence of carbon dioxide, water and sunlight. Autotrophic bacteria also obtain their food by this mode of nutrition. The organisms that make their own food are called autotrophs. All the green plants are called autotrophs. The green plants contain a green pigment called chlorophyll that traps the sunlight. The green plants are also called producers because they make their own food.
• Heterotrophic mode of nutrition: In this mode of nutrition, organisms depend on other organisms for their food. All the animals come in this category. Most of the bacteria and fungi have heterotrophic mode of nutrition because they cannot make their own food. Non green plants are also called heterotrophs. The organisms that cannot make their own food are called heterotrophs.

  The following are the types of heterotrophic nutrition:  

• Saprophytic nutrition: In this mode of nutrition, an organism obtains its food from dead and decaying organic matters such as dead animals, plants, rotten bread, etc. They are called saprophytes. For example, fungi and bacteria. These organisms break down the complex organic molecule into simpler substances and absorb them as their food.
• Parasitic nutrition: In this mode of nutrition, an organism obtains its food from the body of another living organism called host without killing that organism. In this mode of nutrition, the organism harms the host. For example, disease causing bacteria lives in the body of the humans and causes harm to them.
• Holozoic nutrition: In this mode of nutrition, an organism takes the complex organic food materials in its body by the process of ingestion, the ingested food is digested and then absorbed into the body cells of the organism. For example, human beings, dog, amoeba, etc.

  Steps of Nutrition   The following are the steps of more...

Reproduction, Control and Coordination   All the organisms reproduce to continue their existence on the earth. The production of new organism from the existing organisms of the same species is called reproduction. It is a necessary process to maintain the life on the earth. There are several ways through which animals can produce offspring. The two main methods of reproduction are sexual and asexual.   Sexual Reproduction The production of new organism with the use of their sex gametes is called sexual reproduction. This type of reproduction requires two parents who donate genes to the young one, resulting in offspring with a mix of inherited genes. Humans, animals and many other organisms reproduce by this method. Many flowering plants also reproduce by this method.   Asexual Reproduction The production of new organism without the involvement of sex gametes is called asexual reproduction. In this type of reproduction, only a single parent is required.   Types of Asexual reproduction: Fragmentation In fragmentation, parent breaks into different fragments, which eventually forms new individuals. For example, spirogyra.   Regeneration In regeneration, when an animal that is capable of regeneration loses a body part, it can grow a replacement part. If the lost body part contains enough genetic information from the parent, it can regenerate into an entirely new organism. For example, sea stars, flatworms, etc.   Budding In budding, a bulb- like projection or outgrowth arises from the parent body known a bud which detaches and forms a new organism. These buds develop into tiny individuals and when get fully mature.   Vegetative propagation In this type of reproduction, any vegetative part of the plant body like leaf, stem or roots develops into a complete new plant. For example, leaf in bryophyllum, stem in rose bulb in onion, etc.   Spore formation In this mode of reproduction, the organism breaks up into a number of pieces or spores, each of which eventually develops into an organism. Spore formation is a mode of reproduction resembling multiple fission. For example, Ferns, Mosses, Rhizopus, etc.   Sexual Reproduction in Flowering Plants In sexual reproduction, the male cell produced by the male part of the flower and female cell produced by the female part of the flower fuses together. The male and female cells are called gametes. The fusion of male and female gametes is known as fertilization and leads to the formation of single cell, called zygote. The zygote divides repeatedly and gives rise to a new individual.   Structure of a flower: The flower consists of four whorls. The outermost whorl consist of sepals. Then next is petals. Then after that comes stamens and at the centre us the female whorl, called pistil. The pistil can consist of one or many carpels. The carpel has a stalklike style with a sticky tip called the stigma and swollen base called ovary. Inside the ovary, there exists egg like ovules.   more...

Heredity and Evolution     Heredity and Evolution   Heredity The transmission of traits from parents to their offspring is called heredity. It is the continuity of features from one generation to another generation.     Rules for the Inheritance of Traits: Mendel’s Contribution The transmission of genetically controlled traits from one generation to another is called inheritance. Mendelian laws of inheritance states about the way certain characteristics are transmitted from one generation to another in an organism. Mendel used pea plants for his experiments. He studied the colour of flowers, their location on the plant, the shape and colour of pea pods, the shape and colours of seeds and the length of plants stems. Mendel concluded that characteristics are transmitted from one generation to the next in pea plants.   Mendel’s Laws of inheritance: Law I: Law of dominance - It states that when two homozygous individuals with one or more sets of contrasting characteristics are crossed, the characteristics which appear in the F1 hybrids are dominant and those which do not appear in F generation are recessive. Law II: Law of segregation - It states that when a pair of allele is brought together in hybrid, the members of the allelic pair remain together without mixing and separate or segregate from each other when the hybrid forms gametes. Law III: Law of independent assortment - It states that, when a dihybrid organism forms gametes, each allelic pair (or each characteristic), the assortment of alleles of different characteristics during gamete formation is independent of their parental combinations.   Sex determination in human beings A person can have a male sex or a female sex. The process by which the sex of a person is determined is called sex determination. Genetics is involved in the determination of the sex of a person.   Evolution Evolution is the series of gradual changes that take place over millions of years. It is the change in the genetic material of a population of organisms from one generation to another. Genes are the basis of evolution that passes from one generation to another and thus produces an organism's inherited traits. The inherited traits vary within organism. The mechanisms that determine which variant will become more common or rare in a population are natural selection and genetic drift. Natural selection is a process that causes helpful traits to become more common in a population and harmful traits to become rarer. This happens because individuals with useful traits are more likely to reproduce. This clearly indicates that more individuals in the next generation will inherit these traits. Adaptations occur through a combination of successive, small, random changes in traits over many generations and natural selection of the variants best-suited for their environment. Genetic drift is an independent process that produces random changes in the frequency of traits in a population. Genetic drift results from the more...