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For class 9th Science Project

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  • 1. Name Class TeacherSchool_____________________________________

2. The water molecule is formed by thechemical combination of 2 hydrogenatoms and 1 oxygen atom. Water is essential for the existence of life. All bio-chemical reactions take place in awater medium. Nearly 65-70% of the total body weight ofliving beings consists of water. 3. An important feature of water isits polar nature. The water molecule forms an angle,with hydrogen atoms at the tips andoxygen at the vertex. Since oxygen has a higher electronegativity than hydrogen, the sideof the molecule with the oxygenatom has a partial negative charge.An object with such a chargedifference is calleda dipole meaning two poles.The oxygen end is partiallynegative and the hydrogen end ispartially positive, because of thisthe direction of the dipolemoment points towards the oxygen. The charge differences cause water 4. MOLECULAR STRUCTUREOF WATERA molecule is an aggregation of atomic nuclei and electrons that is sufficiently stable to possess observable properties And there are few molecules that are more stable and difficult to decompose than H2O.In water, each hydrogen nucleus is bound to the central oxygen atom by a pair of electrons that are shared between them; chemists call this shared electron pair a covalent chemical bond.In H2O, only two of the six outer-shell electrons of oxygen are used for this purpose, leaving four electrons which are organized into two non-bonding pairs. The four electron pairs surrounding the oxygen tend to arrange themselves as far from each other as possible in order to minimize repulsions between these clouds of negative charge. This would ordinarily result in a tetrahedral geometry in which the angle between electron pairs (and therefore the H-O-H Bond angle) is 109.5 .However, because the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together.The result is a distorted tetrahedral arrangement in which the HOH angle is 104.5 . (Continued in next slide) 5. BECAUSE MOLECULES ARE SMALLER THAN LIGHT WAVES, THEYCANNOT BE OBSERVED DIRECTLY, AND MUST BE "VISUALIZED"BY ALTERNATIVE MEANS. THIS COMPUTER-GENERATED IMAGECOMES FROM CALCULATIONS THAT MODEL THE ELECTRONDISTRIBUTION IN THE H2O MOLECULE. THE OUTER ENVELOPESHOWS THE EFFECTIVE "SURFACE" OF THE MOLECULE ASDEFINED BY THE EXTENT OF THE CLOUD OF NEGATIVE ELECTRICCHARGE CREATED BY THE TEN ELECTRONS. 6. Electrolytes is a substance which conducts electricity either in liquid or in solution formStrong electrolytes Weak electrolytes : A strong electrolyte is A weak electrolyte is an electrolyte that completelyan electrolyte that does not dissociates in solution. Thecompletely dissociate solution will contain in solution. The solution will only ions and no molecules of contain the electrolyte. Strong both ions and molecules of the electrolyte. electrolytes are goodExamples: conductors of electricity. HC2H3O2 (acetic acid),Examples: H2CO3 (carbonic acid), HCl (hydrochloric NH3 (ammonia) are all weak acid), H2SO4 (sulfuric acid), electrolytes. NaOH (sodium hydroxide) and KOH (potassium hydroxide) are all strong electrolyte. 7. 1.Strong Electrolyte -100% dissociation,all ions in solution High Conductivity Na+ Cl- 8. Classification of electrolytes..2.Weak Electrolyte -partial dissociation,slight conductivitymolecules and ions insolutionCH3COOH CH3COO-H+ 9. Non electrolytesA non-electrolyte does not provide ions in a solution and therefore current does not flow through such solution. Examples :-alcohol, carbon tetrachloride, carbon disulphide.Non-electrolyte -No dissociation,all molecules in solution no conductivitysugar 10. Electrolysis of water isthe decomposition ofwater (H2O)into oxygen (O2)and hydrogen gas (H2) due to an electric current being passedthrough the water. 11. F a r a d a y s l a wso fe r la d e y c pt u t r f o r w a ryd h i si t s oFa a so l swl a ws o f e l e c t r o l y s i s i n 1833.F a r a d a y s F i r s tLa w ofEl e c t r ol y s i s :S t a t e me n t :T h ema s s o f a n e l e me n t s w h i c h i sd e p o s i t e d o n a n e l e c t r o d e d u r i n ge l e c t r o l y s i s i s d i r e c t l yp r o p o r t i o n a l t o t h e q u a n t i t y o fe l e c t r i c i t y wh i c h p a s s e st h r o u g h t h e e l e c t r o l y t e .Ex pl a na t i on :I f W i s t h e a mo u n t o f s u b s t a n c e w h i c hl i b e r a t e s o r d e p o s i t e d a t t h ee l e c t r o d e o n p a s s i n g t h e (C o n t i n u e d 12. C o n t d :- As, We c a n w r i t e t h e s t a t e m e n t o f t h ef i r s t l a w o f e l e c t r o l y s i sma t h e ma t i c a l l y a s u n d e r :o r W= Z a tI f 1 a mp e r e e l e c t r i c c u r r e n t p a s s e st h r o u g h t h e e l e c t r o l y t e f o r 1s e c o n d t h e n W=Z I t m e a n s t h a t o np a s s i n g t h e c u r r e n t o f 1 a mp e r e f o r 1s e c o n d t h e we i g h t o f t h e s u b s t a n c ed e p o s i t e d i s e q u a l t o t h ee l e c t r o c h e mi c a l c o n s t a n t . F o rd o i n g t h e c a l c u l a t i o n s o fe l e c t r o c h e mi c a l p r o b l e ms , w e mu s tk n o w t h e u n i t s t o o .Un i to fc h a r g e (Q ) = C o u l o m b (C )u n i t o fm a s s (m ) = K i l o g r a m (k g )u n i t o fc u r r e n t (A ) = a m p e r e (A )u n i t o fe l e c t r o c h e mi c a le q u iv a l e n t (Z ) = k g /C 13. FARADAYS LAWS OF ELECTROLYSIS Faradays Second Law of Electrolysis:.Statement: When the same quantity of electricity is passed throughdifferent electrolytes, the masses of the elements liberated ordeposited are in proportion to the chemical equivalents ofthese elements. Faradays laws are very useful for thedetermination of electrochemical equivalents of differentsubstances. Chemical Equivalent: The chemical equivalent of an element is numerically equal toits relative atomic mass in grams divided by its the valency ofthe ion.Faradays second law of electrolysis can also be stated asunder: (Continued in next slide) 14. EXPLANATION:TAKE THREE SOLUTIONS OF ELECTROLYTES: AGNO3, CUSO4 ANDAL(NO3)3 IN A SERIES, PASS SOME QUANTITY OF ELECTRICITYTHROUGH THEM FOR THE SAME TIME. NOW AG CU AND AL METALSCOLLECT AT THE CATHODE. THEIR MASSES ARE DIRECTLYPROPORTIONAL TO THEIR EQUIVALENT MASSES.ACCORDING TO FARADAY, IF 96,500 COULOMBS (OR 1 FARADAY) ISPASSED THROUGH THESE ELECTROLYTES,WE GET WHICH ARE THE EQUIVALENT MASSES OFAG, CU AND AL RESPECTIVELY. 15. Applications of ElectrolysisIndustrial uses Productionof aluminum, lithium, sodium, potassium, magnesium, calcium Coulometric techniques can be used todetermine the amount of matter transformedduring electrolysis by measuring the amount ofelectricity required to perform the electrolysis Production of chlorine and sodium hydroxide Production of sodium chlorate and potassiumchlorate Production of per fluorinated organiccompounds such as trifluoroacetic acid Production of electrolytic copper as a cathode, Hall-Heroult process for producing from refined copper of lower purity as galuminiuman anode. 16. Electrolysis has many other uses: Electrometallurgy is the process of reduction of metals from metallic compounds to obtain the pure form of metal using electrolysis. For example, sodium hydroxide in its molten form is separated by electrolysis into sodium and oxygen, both of which have important chemical uses. (Water is producedat the same time.)Anodization is an electrolytic process that makes the surface of metals resistant to corrosion. For example, ships are saved from being corroded by oxygen inthe water by this process. The process is also used to decorate surfaces. A battery works by the reverse process to electrolysis. Production of oxygen for spacecraft and nuclear submarines.Electroplating is used in layering metals to fortify them. Electroplating is used in many industries for functional or decorative purposes, as in vehicle bodies and nickel coins.Production of hydrogen for fuel, using a cheap source of electrical energy.Electrolytic Etching of metal surfaces like tools or knives with a permanentmark or logo. Electrolysis is also used in the cleaning and preservation of old artifacts.Because the process separates the non-metallic particles from the metallic ones, it is very useful for cleaning old coins and even larger objects. 17. Electrolytic refining The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode. The electrolyte is an acidic solution of copper sulphate. By passing electricity through the cell, copper is dissolved from the anode and deposited on the cathode. However impurities either remain in solution or collect as an insoluble sludge. This process only became possible following the invention of the dynamo; it was first used in South Wales in 18 18. Electroplating Electrotyping (also Galvanoplasty) is a chemical method forforming metal parts that exactly reproduce a model. The method was invented by Moritz von Jacobi in Russia in1838, and was immediately adopted for applications inprinting and several other fields. As described in an 1890 treatise, electrotyping produces "anexact facsimile of any object having an irregularsurface, whether it be an engraved steel- or copper-plate, awood-cut, or a form of set-up type, to be used for printing; ora medal, medallion, statue, bust, or even a natural object, forart purposes. "[In art, several important "bronze" sculptures created in the19th century are actually electrotyped copper, and not bronzeat all; sculptures were executed using electrotyping at leastinto the 1930s. In printing, electrotyping had become a standard method forproducing plates for letterpress printing by the late 1800s. 19. articles made up ofcheaper metals can beplated with gold &silver.By doing this themetals ap

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