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Note for Applied Chemistry - CHEM by Yasala Vamshidhar

  • Applied Chemistry - CHEM
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Yasala Vamshidhar
Yasala Vamshidhar
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2011. Reference Books: 1. B. Siva Shankar, “Engineering Chemistry”, Tata Mc Graw Hill Publishing Limited, 3rd Edition, 2015. 2. S. S. Dara, Mukkanti, “Text of Engineering Chemistry”, S. Chand & Co, New Delhi, 12 th Edition, 2006. 3. C. V. Agarwal, C. P. Murthy, A. Naidu, “Chemistry of Engineering Materials”, Wiley India, 5th Edition, 2013. 4. R. P. Mani, K. N. Mishra, “Chemistry of Engineering Materials”, Cengage Learning, 3rd Edition, 2015. Web References: 1. www.tndte.com 2. nptel.ac.in/downloads 3. www.scribd.com 4. cuiet.info 5. www.sbtebihar.gov.in 6. www.ritchennai.org E-Text Books: 1. Corrosion.ksc.nasa.gov/electrochem_cells.htm 2. www.science.uwaterloo.ca/~cchieh/cact/applychem/watertreatment.html 3. www.acs.org/content/acs/en/careers/college-to-career/areas-of-chemistry/polymer-chemistry.html 4. www.darvill.clara.net/altenerg/fossil.htm 5. Library.njit.edu/research helpdesk/subject guides/chemistry.php Unit - I 3

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Electro Chemistry and Corrosion Introduction:- Chemistry is the Study of matter, its properties and the changes it may undergo. All matter is electrical in nature. An atom is made up of sub atomic particles like electors, protons and neutrons etc. Electro chemistry is a branch of chemistry which deals with the transformation of electrical energy into chemical energy or chemical into electrical energy. 1.1.1 Concept of electrochemistry: Electrical Conduction: The substances are divided into 4 types depending upon their capability of flow of electrons. i) Conductors: The Substances which allows electricity to pass through them are called conductors. Ex :- Metals, metal sulphides, acids, alkalis, salt sol. and fused salts The electrical conductors are of two types. 1. Metallic or Electronic conductors. 2. Electrolytic conductors ii) Non-conductors: The substances which do not allow electricity are called non-conductors. Ex: Pure water, dry wood, rubber, paper, non-metals etc. iii) Semi conductors: The substances which partially conduct electricity are called semiconductors. The conducting properties of semi-conducting properties are increased by the addition of certain impurities called “dopping”. Ex: ‘si’ and addition of V group elements like ‘p’ ‘si’ produces n-type semi-conductor. On addition of iii group element like ‘B’, Al, ‘si’ produces p-type of semi-conductor. 4

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Differences between Metallic Conductors and Electrolytic Conductors Metallic conductors Electrolytic conductors 1. Conductance is due to the flow of electrons. 1. Conductance is due to the movement of ions in a solution. 2. Chemical reactions take place at the electrodes. 2. It does not result any chemical change. 3. Metallic conduction decreases with increase in temperature. 4. It does not involve any transfer of matter. 3. Electrolytic conduction increases with increase in temperature. 4. It involves transfer of matter. Electrical resistance – ohm’s law. The current strength flowing through a conductor at uniform temperature is directly proportional to the potential difference applied across to conductor. VαI I → current strength V → potential difference. V=IR R-Proportionality const which is called resistance R=V /I Units for Resistance is ohm 5

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Specific resistance (or) Resistivity: Ohm found that the solution of electrolyte also offers resistance to flow of current in the solution. “The resistance (R) of a conductor is directly proportional to its length and inversely proportional to its cross sectional area (a)” Rα Rαa Rα R= ρ → ρ - Specific resistance. cm and a= 1cm2 then R = ρ If then the specific resistance is defined as “The resistance offered by a material of unit length and unit area of cross section is called specific resistance” ρ = R/ /a = R×a/ Units: ohm × cm2/cm = ohm cm Conductance: The reciprocal of resistance is called Conductance L= Units: ohm -1(or) mho (C.G.S) Siemens (S) (M.K.S) Specific Conductance (or) Conductivity: Reciprocal of specific resistance is known as specific conductance. 1/R = 1/ρ ×1/ L= k.a/l K = L/a/l = L× l/a If l = 1cm, a =1 cm2 then K = L, then the specific conductance is defined as. 6

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