9th class chemistry chapter 7 notes
Important Notes of 9th class chemistry chapter 7 notes Urdu Medium written by Honorable Sir M. Shahid Suib. These notes are very helpful in the preparation of Electrochemistry Class 9th for students of the 9th class chemistry chapter 7 notes Urdu Medium and these are according to the paper patterns of all Punjab boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Complete Exercise MCQs of Chapter No.7: Electrochemistry in Urdu Medium
- Complete Exercise Short Questions with Answers of Chapter No.7: Electrochemistry in Urdu Medium
- Major Concepts: Oxidation and reduction, Oxidation states and rules for assigning oxidation states, Oxidizing and reducing agents., Oxidation - reduction reactions, Electrochemical cells, Electrochemical industries, Corrosion and its prevention
- oxidation and reduction reactions class 9: One concept of oxidation and reduction is based upon either addition or removal of oxygen or addition or removal of hydrogen in a chemical reaction. So according to this concept:
- Oxidation is defined as addition of oxygen or removal of hydrogen during a chemical reaction. Reduction is defined as addition of hydrogen or removal of oxygen during a chemical reaction. Both of these processes take place simultaneously in a reaction, we can say where there is oxidation there is reduction.
- Let us first discuss an example to understand the concept based on addition and
removal of oxygen. A reaction between zinc oxide and carbon takes place by the
removal of oxygen (reduction) from zinc oxide and addition of oxygen (oxidation) to
carbon.
- Oxidation and Reduction in Terms of Loss or Gain of Electron: In chemistry, there are many chemical reactions which do not involve oxygen or hydrogen, but they are considered redox reactions. To deal with these reactions, new concept 'loss or gain of electrons' is used. Therefore, reactions which involve 'loss or gain of electrons' are also called oxidation and reduction reactions.
- OXIDATION STATE AND RULES FOR ASSIGNING OXIDATION STATE: Oxidation state or oxidation number (O.N.) is the apparent charge assigned to an atom of an element in a molecule or in an ion.
- Rules for assigning oxidation numbers (O.N.)
- The oxidation number of all elements in the free state is zero.
- The oxidation number of an ion consisting of a single element is the same as the charge on the ion.
- The oxidation number of hydrogen in all its compounds is +1. But in metal hydrides it is -1.
- In neutral molecules, the algebraic sum of the oxidation numbers of all the elements is zero.
- oxidizing and reducing agents class 9: An oxidizing agent is the specie that oxidise a substance by taking electrons from it. The substance (atom or ion) which is reduced itself by gaining electrons is also called oxidizing agent.
- Reducing agent is the specie that reduces a substance by donating electron to it.The substance (atom or ion) which is oxidized by losing electrons is also called reducing agent.
- oxidation reduction reactions class 9: Chemical reactions in which the oxidation state of one or more substances changes are called oxidation-reduction or redox reactions.
- Electrochemical cells class 9: Electrochemical cell is a system in which two electrodes are dipped in the solution of an electrolyte which are connected to the battery.
- Electrochemical cell is an energy storage device in which either a chemical reaction takes place by using electric current (electrolysis) or chemical reaction produces electric current(electric conductance).
- Electrochemical cells are of two types. i. Electrolytic cells ii. Galvanic cells
- Concept of Electrolytes: The substances, which can conduct electricity in their aqueous solutions or molten states, are called electrolytes.
- For example, solutions of salts, acids or bases are good electrolytes. The electricity cannot pass through solid NaCl but in aqueous solution and in molten state, it does conduct. Electrolytes are classified into two groups depending upon their extent of ionization in solution.
- Strong Electrolytes: The electrolytes which ionize almost completely in their aqueous solutions and produce more ions, are called strong electrolytes.
- Weak Electrolytes: The electrolytes which ionize to a small extent when dissolved in water and could not produce more ions are called weak electrolytes.
- Non-Electrolytes: The substances, which do not ionize in their aqueous solutions and do not allow the current to pass through their solutions, are called non-electrolytes.
- Electrolytic cells: The type of electrochemical cell in which a non-spontaneous chemical reaction takes place when electric current is passed through the solution, is called an electrolytic cell.
- Important Questions of Electrochemistry: