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SS 2 Chemistry (1st Term)

Chemistry

FARADAY’S LAWS OF ELECTROLYSIS AND CALCULATIONS

Charge flow during electrolysis The coulomb is the electrolytic unit of charge. A current of one ampere is the rate of flow of charge equal to one coulomb per second. The charge is calculated from the knowledge of the number of seconds for which a steady current is passed. Current in circuit Time taken Total charge 1 ampere 1 second 1 coulomb 1 ampere 10 seconds 10 coulombs 20 amperes 10 seconds 200 coulombs A amperes t seconds At coulombs   Therefore charge = quantity of electricity (Q) = I × t Q = I × t   Flow of charge required to liberate 1 mole of element during electrolysis Electrolysis always produces chemical reactions. Consider a reaction (at cathode) in which one mole of silver Ag+ ions is discharged and deposited. Ag+ + e– → Ag(s) In this case, 1 mole of electrons (e–) is required to discharge 1… Read More »FARADAY’S LAWS OF ELECTROLYSIS AND CALCULATIONS

Chemistry

APPLICATIONS OF ELECTROCHEMICAL CELLS

The importance of electrochemical cells or galvanic cells lies in their ability to provide us with a portable source of electrical energy. We have already studied that indirect redox reaction is, primarily, the basis of all the electrochemical cells Quite often, we use the term battery to represent the arrangement of two or more galvanic cells connected in series. However, in practice the redox reaction used should give the arrangement which fulfills the following requirements: It should be light and compact; Its voltage should not vary appreciably during its use; It should provide power for a longer period; and It should be rechargeable. APPLICATIONS OF THE ELECTROCHEMICAL SERIES Some of the important applications of the electrochemical series have been discussed as follows: Calculation of the standard EMF of the cell. From the electrochemical series, the standard reduction potentials of electrodes are found out. The electrode with higher reduction potential is… Read More »APPLICATIONS OF ELECTROCHEMICAL CELLS

Chemistry

ELECTROCHEMISTRY

It is a well known fact that energy menifests itself in different forms which are interconvertible into one another. Among different forms of energy, the electrical energy plays a very significant role in our daily life. Many chemical transformations and industrial processes are based on electrical energy and its relationship with chemical energy. There are large number of spontaneous redox reactions which form the basis of production of electrical energy. The device in which such chemical processes are carried out is called electrochemical cell or galvanic cell. For example, Daniell cell is based on the following redox reaction: Cu2(aq) + Zn(s) à Cu(s) + Zn2+ + Electrical Energy At the same time many of the non-spontaneous redox reactions can be made to occur by the use of electrical energy. Some examples are: The branch of chemistry which deals with the study of relationship between electrical energy and chemical energy and… Read More »ELECTROCHEMISTRY

Chemistry

ELECTROLYTIC CELLS AND ELECTROLYSIS OF SPECIFIED ELECTROLYTES

The passage of electricity through the electrolytes in their molten or dissolved state can cause chemical changes under suitable conditions. For example, the passage of electricity through the acidified water results in the formation of hydrogen and oxygen gases. The process of chemical decomposition of the electrolyte by he passage of electricity through its molten or dissolved state is called electrolysis.   ELECTROL YTIC CELL The device in which the process of electrolysis is carried 1ut is called electrolytic cell. It consists of: (i) Electrolytic tank, which is made of some nonconducting materials like glass, wood or bakelite. (ii) Electrolyte in its dissolved state or molten state. (iii) Source of electricity; an electrochemical cell or battery. (iv) Two metallic rods, suspended in the electrolyte and connected to the battery through conducting wires. These rods are called electrodes. The electrode connected to the negative terminal of battery is called cathode while… Read More »ELECTROLYTIC CELLS AND ELECTROLYSIS OF SPECIFIED ELECTROLYTES

Chemistry

Electrolysis

When an electric current is passed through an electrolyte solution, the ions of the electrolyte undergo chemical changes at the respective electrodes. The chemical reaction carried out by passing electricity is called electrolysis. it is important that we familiarize ourselves with different terms that we are going to use to explain different phenomena. It is crucial that the definitions and meanings of these terms be understood at the outset in order that concepts defined in this chapter are easily and clearly apprehended. These terms are given hereunder: Electrolysis: decomposition of a compound in solution or molten state by passing electricity through it. Conductor: a solid substance that allows electricity to pass through it. All metals are included in this class. Non-conductor or insulator: a solid substance that does not allow electricity to flow through it. All non-metals fall in this class. Electrolyte: a substance which, when dissolved or molten, conducts… Read More »Electrolysis

Chemistry

IONIC THEORY

IONIC THEORY To account for the phenomena of electrolysis the Ionic Theory was put forward by Arrhenius in 1880. The theory states that electrolytes are made up of ions, which are built up in certain patterns called crystal lattice. When these substances dissolve in water, the structure is destroyed and the ions are set free to move. Concentrated mineral acids such as sulphuric acid, hydrochloric acid and nitric acid do not contain ions but they consist of molecules. However, when they are diluted, the molecular structure is destroyed and ions are formed. THE MECHANISM OF ELECTROLYSIS The conductivity of ionic compounds is explained by the fact that ions move in a particular direction in an electric field. This can be shown in experiments with coloured salts. For example, copper (II) chromate (VI) (CuCrO4) dissolves in water to give a green solution. This solution is placed in a U-tube. A colourless… Read More »IONIC THEORY

Chemistry

BALANCING OF REDOX REACTIONS

Balancing by Ion Electron or Half Reaction Method We are familiar with the balancing of chemical equations by inspection method. However, inspection method may not be useful for balancing the redox equations because in these equations, we have to keep in mind the conservation of charge as well as conservation of mass. The redox equations, are therefore, are balanced by using the concept of half equations and following certain set of rules. One of the methods used for balancing redox reactions is called ion-electron method.    BALANCING BY ION ELECTRON OR HALF REACTION METHOD We know that during redox reactions there is a change in oxidation number of the elements due to the transference of electrons. The basic principle involved in balancing the redox equation is that the number of electrons lost during oxidation is equal to the number of electrons gained during reduction.   STEPS INVOLVED IN BALANCING REDOX… Read More »BALANCING OF REDOX REACTIONS

Government (Secondary School)

Concept of Oxidation and Reduction

Classical Concept of Oxidation and Reduction In our daily life we come across processes like rusting of iron articles, fading of the colour of the clothes, burning of the combustible substances such as cooking gas, wood, coal, etc. All these processes fall in the category of redox reactions. A large number’ of industrial processes like, electroplating, extraction of metals like aluminium and sodium, bleaching of wood pulp, manufacture of caustic soda, etc., are also based upon the redox reactions: Redox reactions also form the basis of electrochemical and electrolytic cells. In the present unit we shall understand the meaning of oxidation, reduction, oxidising agents and reducing agents.    CLASSICAL CONCEPT OF OXIDATION AND REDUCTION According to classical concept following definitions were proposed to explain the process of oxidation and reduction. Oxidation: It is a process of chemical addition of oxygen or any electronegative radical or removal of hydrogen or any… Read More »Concept of Oxidation and Reduction

Chemistry

PERIODIC TRENDS IN PHYSICAL PROPERTIES

Most of the properties of the elements such as atomic volume, atomic size, ionization enthalpy, electron affinity and electronegativity are directly related to the electronic configuration of the atoms. These properties undergo periodic variation with the change in the atomic number within a period or a group. These properties indirectly control the physical properties such as melting point, boiling point, density, etc. Let us now proceed to study the variation of some of the atomic properties in the periodic table. ATOMIC RADIUS The atomic size is very important property of the atoms because it is related to many other chemical and physical properties. In dealing with atomic size, the atom is assumed to be a sphere and its radius determines the size. In general, atomic radius is defined as the distance of closest approach to another identical atom. However, it is not possible to find precisely the radius of the… Read More »PERIODIC TRENDS IN PHYSICAL PROPERTIES

Chemistry

PERIODICITY

THE NEED FOR CLASSIFICATION OF ELEMENTS Before the beginning of eighteenth century, only a very few elements were known and it was quite easy to study and remember their individual properties. In 1800, only 31 elements were known. This number of elements grew to 63 by 1865. With the discovery of large number of elements it became difficult to study individually the properties of these elements and their compounds. At this stage, the scientists felt the need of some simple methods to facilitate the study of the properties of various elements and their compounds. After numerous attempts the scientists were ultimately successful in arranging the elements in such a way so that similar elements were grouped together and different elements were separated. The arrangement of elements in such a way that the similar elements fall within same vertical group and the dissimilar elements ate separated, is known as classification of elements.… Read More »PERIODICITY

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