Current Affairs 10th Class

 Acids, Bases and Salts            

• Acids

The term acid has its origin in the latin word acidus, meaning sour.  

• An acid is a substance that has a sour taste. It is defined as a compound which contains replaceable hydrogen in it.

 

• Acids that contain both hydrogen and oxygen are called oxyacids.

 

• Acids that contain hydrogen and other non-metallic elements except oxygen are called hydracids.

 

• Properties of Acids

Acids have a sour taste, turn blue litmus to red, conduct electricity and react with metals to form salt and hydrogen gas.  

• Bases

A base is a substance, usually the oxide or the hydroxide of a metal, which can react with an acid to produce salt and water.  

• Alkalis are bases that are soluble in water.

 

• The strength of a base is determined by the amount of hydroxide ions that the base provides when dissolved in water.

 

• Properties of Bases

Bases have bitter taste, soapy to touch, turn red litmus to blue and react with metals to form hydrogen gas.  

• pH Scale

In 1909 Sorensen devised a scale (known as pH scale) on which the strength of acid solutions as well as basic solutions could be represented by making use of the hydrogen ion concentrations in them.  

• The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. In the term pH, letter 'p' stands for a German word 'potenz' which means 'power' and letter H stands for hydrogen ion concentration\[[{{H}^{+}}]\]

(i) Acids (or acidic solutions) have a pH of less than 7. (ii) Bases (or basic solutions) have a pH of more than 7. (iii) Neutral substances have a pH of exactly 7.

 Metals and Non- Metals  

• Metals and non-metals: On the basis of properties, all the elements can be divided into two main groups: metals and non-metals.

 

• Sodium, Potassium, Calcium and Magnesium form positive ions. A majority of the known elements are metals. All metals are solids, except mercury which is a liquid metal.

 

• The most abundant metal in the earth's crust is aluminium.

 

• Though non-metals are small in number as compared to metals, they play a very important role in our daily life.

 

• The most abundant non-metal in the earth's crust is oxygen.

 

• Metallurgy: Metallurgy is the branch of chemistry that deals with the extraction of metals from their ores.

 

• Physical Processes involves crushing, grinding and concentration of the ore, gravity separation, froth floatation and electromagnetic separation.

 

• Chemical Processes involve roasting, calcination, reduction of metallic oxide to free metal, reduction of ore and refining of metals.

 

• Refining of metals: Metals obtained by the above processes contain impurities such as presence of other metals, non-metals like silicon or phosphorus, unreduced oxides and sulphides of the metal. Following processes involve refining of various metals:

  (i) Liquidation: This method is used to refine metals having a low melting point, e.g., lead and tin. (ii) Distillation: Used to refine volatile metals like mercury and zinc which contain non volatile impurities. (iii) Oxidation: Used to refine metals containing volatile impurities, which are easily oxidised, e.g., pig iron. (iv) Electro - refining: This is an economical and effective method for purifying metals, e.g., copper, aluminium, lead.  

• Reactivity series (or activity series) of metals

 Carbon and Its Compounds  

• Carbon is a non-metal. All living things, plants and animals are made up of carbon based compounds which are called organic compounds.

We can test the presence of carbon in a material on the basis of the fact that carbon and its compounds burn in air to give carbon dioxide gas which turns lime water milky.  

• The atomic number of carbon is 6, i.e., K shell has 2 electrons and L shell has 4 electrons.

 

• Occurrence of Carbon

Carbon occurs in nature in the 'free state' (as element) as well as in the 'combined state' (in the form of compounds with other elements).  

• Allotropes of Carbon

The three allotropes of carbon are diamond, graphite and buck minster fullerene.  

• Catenation and Tetravalency

 

• The two characteristic properties of carbon which leads to the formation of o very large number of organic compounds are catenation and tetravalency.

 

• Carbon atoms can link with one another by means of covalent bonds to form long chains (or rings) of carbon atoms.

 

• When carbon atoms combine with one another, three types of chains are formed. These are : (i) straight chains, (ii) branched chains, and (iii) closed chains or ring type chains.

 

• Hydrocarbons

Hydrocarbons are compounds of carbon and hydrogen. They can be saturated or unsaturated.  

• Saturated Hydrocarbons (Alkanes)

 

• A hydrocarbon in which carbon atoms are bonded to hydrogen atoms by only single bonds is called a saturated hydrocarbon. Saturated hydrocarbons are also called alkanes.

 

• Unsaturated Hydrocarbons (Alkenes and Alkynes)

A hydrocarbon in which two carbon atoms are bonded by a 'double bond' or a 'triple bond' is called an unsaturated hydrocarbon. Ethene \[({{H}_{2}}C=C{{H}_{2}})\]and ethyne\[(HC\equiv CH)\]are two important unsaturated hydrocarbons, because ethene contains a double bond and ethyne contains a triple bond between two carbon atoms.  

• Isomers

The organic compounds having the same molecular formula but different structures are known as isomers. Isomerism is possible only with hydrocarbons having 4 or more carbon atoms.  

• Normal-butane has a straight chain structure whereas iso-butane has a branched chain structure.

 

• Homologous series

A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by - CK, group.  

• Coal and petroleum

Coal is a complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon. Small amounts of nitrogen and sulphur compounds are also present in coal.  

• Petroleum is a complex mixture of several solid, more...

Periodic Classification of Elements  

• Scientists have discovered 118 elements till date. Some of these elements occur in free state and some in combined state.

 

• Lavoisier classified elements into metals and non-metals.

 

• In 1817, German chemist Johann Wolfgang Dobereiner proposed Law of Triads.

 

• In a Dobereiner's triad, the atomic weight of middle element is nearly the arithmetic mean of the first and the third element.

 

• In 1866, John Newlands, an English chemist showed that, when elements are arranged in the order of their increasing atomic masses, the eighth element, starting from a given element is a kind of repetition of the first one like the eighth one in an octave of music. Newlands' law is known as law of octaves.

 

• Mendeleev and Lother Meyer used atomic weights to classify elements.

 

• Mendeleev's periodic law states that "the properties of elements are the periodic functions of their atomic masses Mendeleev's periodic table corrected the wrongly assigned masses of some elements. He predicted the properties of some undiscovered elements such as eka-boron, eka-aluminium, etc. Mendeleev's periodic table contains vertical columns called "groups" and horizontal rows called "periods"

 

• Modern periodic table is divided into 7 periods and 18 groups. The first six periods contain 2,8,8,18,18 and 32 elements respectively. The 7th period is incomplete. Lanthanoids and actinoids are placed at the bottom of the periodic table in separate blocks.

 

• Based on the electronic configuration, elements are classified into 4 types: inert gases, representative elements, transition elements and inner transition elements.

 

• The maximum number of electrons that a shell can accommodate is determined by the formula\[\text{2}\,{{\text{n}}^{\text{2}}}\], where 'n' represents the shell number from the nucleus.

 

• The valency of an atom can be determined by the number of electrons it loses or gains or shares while combining with other atoms.

 

• Atomic size is the distance between the centre of the nucleus and outermost shell of an isolated gaseous atom.

 

• Atomic radius decreases from left to right in a period and in a group it increases from top to bottom.

 

• An element which shows both metallic and non-metallic characters is called a metalloid or a semi-metal.

 Life Processes  

• The basic functions performed by living organisms to maintain their life on this earth are called life processes.

 

• For life to continue, processes like nutrition, respiration, transport of materials within the body and excretion of waste products are necessary.

 

• Food is a kind of fuel which provides energy to all the living organisms.

 

• A nutrient can be defined as a substance which an organism obtains from its surroundings and uses it as a source of energy or for the biosynthesis of its body constituents.

 

• Nutrition is a process of intake of nutrients by an organism as well as the utilisation of these nutrients by the organism. There are mainly two modes of nutrition: Autotrophic and heterotrophic.

 

• Different steps in the process of nutrition in animals are ingestion, digestion, absorption, assimilation and egestion.

 

• Autotrophic nutrition involves the intake of simple inorganic materials from the environment and using energy source from the sun to synthesise complex, high energy organic material.

 

• Photosynthesis is the process by which plants, capture solar energy to convert\[C{{O}_{2}}\]into simple sugars.

\[6C{{O}_{2}}+12{{H}_{2}}O\xrightarrow[Chlorophyll]{Sunlight}{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{O}_{2}}+6{{H}_{2}}O\]  

• Heterotrophic nutrition involves the intake of complex materials prepared by other organisms. The heterotrophic mode of nutrition is of three types: Saprotrophic, parasitic and holozoic nutrition.

 

• The food eaten by human beings is broken down by various steps along the alimentary canal by the action of digestive enzymes.

 

• The process of releasing energy from food is called respiration.

 

• During the process of respiration complex organic compounds such as glucose is broken down to provide energy in the form of ATP. ATP is used to provide energy for other reactions in the cell.

 

• Respiration in organisms is of two types aerobic and anaerobic respiration.
• The transport of materials such as food, oxygen, energy and excretory products is a function of the circulatory system in human beings.

 

• The transport of water, minerals, food and other materials is a function of the vascular tissues like xylem and phloem in plants.

 

• Excretory products in the form of soluble nitrogen compounds are removed by the nephrons in the kidneys of human beings.

 

• Plants store waste material such as gum and resin in the vacuoles of cells.

Control and Co-ordination  

• The working together of various organ systems is called co-ordination. Control and coordination are the functions of the nervous system and of hormones.

 

• The nervous system in human beings consists of three main portions: central nervous system, peripheral nervous system and autonomic nervous system.

 

• The nervous system is made up of several functional units called neurons or nerve cells. A nerve cell is basically made up of a cell body or cyton with dendrites, axon or nerve fibres.

 

• Two neurons are connected only by the passage of impulses across neuromuscular junction which is called synapse.

 

• The information passing through neurons is in the form of chemical and electrical signals called nerve impulse.

 

• Chemical substance which transmits the message from one nerve cell to another is known as neurotransmitter or chemical transmitter, e.g., Acetylcholine.

 

• The nerves that carry impulses from brain or spinal cord to effector organs are called efferent nerves or motor nerves. Nerves from receptors and sense organs to a specific area in brain and spinal cord are called sensory or afferent nerves, e.g., cranial nerves.

 

• A mixed nerve has both sensory and motor nerve fibres, g., spinal nerves.

 

• The central nervous system consists of brain and spinal cord.

 

• Brain is enclosed in a protective covering called cranium.

 

• The outer brain consists of grey matter. All the cell bodies or cytons are present in this part. The inner part of brain is made up of white mater and it consists of axons.

 

• The ridges of brain are called gyri and the grooves are called sulci.

 

• Brain consists of three parts: fore brain, mid brain and hind brain. The fore brain is the largest part of brain and it consists of olfactory lobes, cerebrum and diencephalon. Cerebrum is the seat of intelligence and memory. The mid brain consists of optic lobes and cerebral peduncles. The hind brain consists of cerebellum, pons varoli and medulla oblongata.

 

• Medulla oblongata is concerned with respiration, heartbeat, blood pressure, temperature and secretions by salivary glands.

 

• Spinal cord is the extension of medulla oblongata and is protected by vertebral column. It is concerned with reflex actions.

 

• Cerebrospinal fluid serves as a shock absorber and protects brain.

 

• The peripheral nervous system consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The tenth cranial nerve is called vagus. It controls the rate of heart beat.

 

• The autonomic nervous more...

 Reproduction    

• The phenomenon of the formation of new individuals from the existing ones to increase the population is called reproduction.

 

• The process of reproduction ensures the continuity of a race and the perpetuation of characteristics of the species and particularly the parent organisms.

 

• Reproduction can be broadly grouped into two types: asexual reproduction and sexual reproduction.

 

• Sexual reproduction is the process during which a new individual is formed by the fusion of a male reproductive cell with a female reproductive cell.

 

• Asexual reproduction is a mode of reproduction by which offsprings arise from a single parent and inherit the genes of that parent only.

 

• Fertilisation is the fusion of gametes to produce a new organism.

 

• Various organisms use different modes of reproduction depending on their body design.

 

• Different forms of asexual reproduction :

 

Binary fission	e.g., amoeba.
Budding	e.g., hydra.
Spore formation	e.g., fungi, fern and moss.
Vegetative reproduction	e.g., bulb of onion, stem tuber, etc.
Regeneration	e.g., planaria, starfish etc.

 

• The roots, stems and leaves of some plants develop into new plants through vegetative propagation.

 

• The different parts of the human male reproductive system are seminal vesicle, scrotum, penis, testis, prostate gland, sperm duct, sperm (male gamete).

 

• Parts of the human female reproductive system are uterus, cervix, fallopian tube, ovary, vagina.

 

• Reproduction in flowering plants involves pollination or the transfer of pollen grains from the anther to the stigma. This is followed by fertilisation.

 Heredity and Evolution    

• Variations that arise during the process of reproduction can be inherited.

 

• These variations may lead to increased survival of the individuals.

 

• Sexually reproducing individuals have two copies of genes for the same trait. If the copies are not identical, the trait that gets expressed is called the dominant trait and the other is called the recessive trait.

 

• Traits in one individual may be inherited separately giving rise to new combinations of traits in the offspring in sexual reproduction.

 

• Sex is determined by different factors in various species. In human beings, the sex of the child depends on whether the paternal chromosome is X (for girls) or Y (for boys).

 

• Variations in the species may confer survival advantages or merely contribute to the genetic drift.

 

• Changes in the non-reproductive tissues caused by environmental factors are not inheritable.

 

• Speciation may take place when variation is combined with geographical isolation.

 

• Evolutionary relationships are traced in the classification of organisms.

 

• Tracing common ancestors back in time leads us to the idea that at some point of time, nonliving material must have given rise to life.

 

• Evolution can be worked out by the study of not just living species, but also fossils.

 

• Complex organs may have evolved because of the survival advantage of even the intermediate stages.

 

• Organs or features may be adapted to new functions during the course of evolution. For example, feathers were thought to have been initially evolved for warmth and later adapted for flight.

 

• Evolution cannot be said to 'progress' from 'lower' forms to 'higher' forms. Rather, evolution seems to have given rise to more complex body designs even while the simpler body designs continue to flourish.

 

• The study of the evolution of human beings indicates that all of us belong to a single species that evolved in Africa and spread across the world in stages.

 Our Environment  

• Environment is the physical and biological world we live in. Biosphere is the total sum of all ecosystems.

 

• A community is a group of different kinds of animal and plant populations living together in a given area.

 

• An ecosystem is defined as a group of organisms interacting among themselves and with their environment.

 

• The biotic components of an ecosystem include producers, consumers and decomposers.

 

• Organisms which feed upon plants consumer animals for food are called e.g., herbivores and carnivores.                                

 

• Decomposers are organisms which bring about the decay and putrefaction of the dead bodies of plants and animals.

 

• A food chain is a sequence of organisms that feed on one another and consists of producers, primary, secondary and tertiary consumers. Several food chains are linked together to form a food web.

 

• The ultimate source of energy for an ecosystem is the Sun. The total energy available at each level in an ecosystem is called tropic level.

 

• The organic molecules formed in plants are partly used in catabolic processes and the rest are stored in the body in the form of biomass. The storage of energy in this form is called gross or net primary productivity.

 

• The number of individuals of different tropic levels is called ecological pyramid.

 

• Ecological pyramids are of three types: pyramid of numbers, pyramid of energy and pyramid of biomass.

 

• Pollution is the undesirable change in the physical, chemical and biological constituents of air, water and soil. It is of different types: air pollution, water pollution, soil or land pollution, noise pollution, radiation pollution and thermal pollution.

 

• Hydrocarbons emitted in huge quantities by the burning of petrol in the automobiles combine with\[N{{O}_{2}}\]and produce photochemical smog.

 

• \[S{{O}_{2}}\]and\[N{{O}_{2}}\]combine with the water vapours present in the air to form acid rains which affect both flora and fauna due to air pollution.

 

• Ozone layer protect us from UV rays.

 

• Chlorofluorocarbons lead to ozone layer depletion.

 

• The excess of \[C{{O}_{2}}\]present in air leads to greenhouse effect thus leading to global warming (increase in the average temperature of the earth).

   

 Management of Natural Resources  

• Conservation of environment is very essential for the survival of human race. The resources should be managed in such a way that it may give maximum benefits to the present generation while maintaining its potential to meet the requirements of the future generation.

 

• Growing population, agriculture, industrialisation and urbanization have led to the exploitation and the consequent depletion of natural resources.

 

• When left undisturbed nature replinishes its resources by recycling. Over exploitation of environment depletes natural resources and disturbs the recycling process.

 

• Natural habitats of plants and animals have been replaced by industries, roads, cities and big towns. Big dams have been constructed in order to generate more electricity for the industries. Water bodies have either dried or been polluted. So we can conclude that development has taken place at the cost of environmental degradation.

 

• Human activities like washing clothes, immersion of ashes or unburnt corpses, industrial wastage and dumping of untreated sewage into the rivers cause water pollution.

 

• Sustainable development implies a change in all aspects of life. It encourages forms of growth that meet current basic needs.

 

• The three R's to save the environment ar reduce, recycle and reuse.

 

• Industrial development, increase in population, and to fulfill the fuel needs and timber requirements, over grazing and mining are responsible for deforestation.

 

• Replenishment of forests ought to be the first priority. They restore ecological balance of all ecosystems and maintain biological diversity.