Chemistry For Kids 2boq

Written by: - SHAHZAD IFTIKHAR # 0313-7891989, 0333-5319544 e-mail: [email protected] website: www.eservicespakistan.com CHEMISTRY FOR 9TH CLASS (UNIT # 8) ============================================================ Read Instructions before study: • Bullet means you have to write the answer in paragraph shape and you could not change the sequence. Bullets are used only for your ease. i) Roman numbered, question may be written as it is. However sequence can be changed. *** This item should not be written in answer. It is just a hint for you. Pay more attention on the bold text in answers. =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=

THEORY Question: Define Electrochemistry? The branch of chemistry in which chemical energy is converted into electrical energy or electrical energy is converted into chemical energy is called electrochemistry. Question: Define conductor and insulator? i) The substances through which electric current can are called conductors i.e. Copper, Aluminium, Iron etc. ii) The substances through which electric current cannot are called insulators or non-conductors. i.e. rubber, plastic, wood etc. Question: Define a Cell? A vessel in which oxidation-reduction reaction takes place at electrodes is called cell. Question: Define Electrolysis? When electricity is ed through fused ionic compounds or their aqueous solutions, they are decomposed into their constituents. Such compounds are called Electrolytes and the process is called Electrolysis. Question: Define Electrolyte and also write its types? The compounds in molten state or in aqueous solution through which electricity can are called electrolyte. And the compounds through which electricity cannot are called non-electrolyte. Strong Electrolyte: Ionization is complete in these electrolytes. For example, in a dilute solution of NaCl there will no formula unit present. Their examples of strong electrolytes are mineral acids, caustic alkalies and their salts. Weak Electrolyte: Ionization is incomplete in these electrolytes. Their examples are ammonium hydroxide, tartaric acid, citric acid and carbonic acid. Question: Define Electrodes? Electrodes are the terminals of the battery at which ions are deposited during the process of electrolysis. They are: Anode: It is a positive electrode through which electrons enter the external circuit. Cathode: It is a negative electrode through which electrons leave the external circuit. ============================================================ Visit www.eservicespakistan.com for Notes, Syllabus, Old Papers, Home Tuitions, Jobs & much more (Page 1 of 6)

Written by: - SHAHZAD IFTIKHAR # 0313-7891989, 0333-5319544 e-mail: [email protected] website: www.eservicespakistan.com CHEMISTRY FOR 9TH CLASS (UNIT # 8) ============================================================

Question: On which factors substances librated at electrodes? During electrolysis the quantities of substances librated at electrodes depend upon the following factors: i) The quantity of current ed. ii) Time duration of ing the current at a uniform rate. iii) Charge on the ions being deposited. Question: Define oxidation and reduction? Oxidation: - A chemical reaction in which: i) Oxygen is added ii) Hydrogen is removed iii) Electrons are lost. Reduction: - A chemical reaction in which: i) Oxygen is removed. ii) Hydrogen is added. iii) Electrons are absorbed. Question: Define Ionization? An electrolyte splits up into charged particles upon heating or in its aqueous solution. This process is called ionization. Question: Describe in detail the Ionic Theory to explain electrolysis? OR Arrhenius theory of ionization? In 1887, Arrhenius, a Swedish chemist, put forward his ionic theory to explain the process of electrolysis. According to this theory: i) When electrolyte are fused or dissolved in water, they are split into positive and negative ions. This process is called ionization. ii) The total positive charge is equal to the total negative charge and the solution is electrically neutral. iii) Metallic ions, ammonium ions and hydrogen ions carry positive charge while on metallic ions and hydroxide ions carry negative charge. iv) The number of electrical charges present on any ion is equal to the valency of the atom or the radical. v) The properties of ions are different from the properties of the related atoms. vi) Ions move in all possible directions in fused salts or in aqueous solutions of salts. vii) When an electric current is ed through an electrolyte, the positive ions are attracted towards the cathode while the negative ions tend to move towards the anode. Question: Define Degree of ionization? The level to which an electrolyte can ionize in water is called its degree of ionization. Degree of Ionization = Number of molecules which ionize Total number of molecules ============================================================ Visit www.eservicespakistan.com for Notes, Syllabus, Old Papers, Home Tuitions, Jobs & much more (Page 2 of 6)

Written by: - SHAHZAD IFTIKHAR # 0313-7891989, 0333-5319544 e-mail: [email protected] website: www.eservicespakistan.com CHEMISTRY FOR 9TH CLASS (UNIT # 8) ============================================================

Question: Explain the process of electrolysis of water? i) Water is weak electrolyte. It ionizes in the following way: H2O <----------------> H+ + OHii) In pure water, out of 6x108 molecules only one molecule is ionized. iii) If hydrogen or hydroxide ions are removed from the above reaction, more water molecules are ionized. iv) A few drops of sulphuric acid are added in water to increase its conduction. (***Draw fig here). v) Both the electrodes used in this cell are made of platinum. vi) On ing the electric current, hydrogen ions move towards the cathode, where they pick up electrons and are converted into hydrogen atoms. Reaction at cathode: H+ + e-------------> H H+H -------------> H2 Reaction at Anode: OH-------------> OH + e2OH -------------> H2O + O O+O -------------> O2 Question: Explain the process of electrolysis of aqueous solution of Sodium Chloride (NaCl)? i) In this process cathode is used of plantium while anode is used of carbon. ii) Carbon anode is used to avoid the reaction with chlorine gas. iii) Following ions are present in solution a. Na+, Cl- (From sodium chloride) b. H+, OH- (From Water) + iv) Na and H+ ions both migrate towards cathode. Reaction at Cathode: H+ + e-------------> H H+H -------------> H2 Reaction at Anode: Cl-------------> Cl + eCl + Cl -------------> Cl2 Question: Explain the process of electrolysis of Fused Sodium Chloride (NaCl)? i) A reactive metal sodium is obtained by the electrolysis of fused sodium chloride. ii) The cell used for this process is called Down’s Cell. (***Draw Fig here) iii) A graphite anode and steel cathode is used in this process. iv) The electrolysis gives sodium metal and chlorine gas as products. v) It is necessary to keep these products separate, otherwise they will react again to give sodium chloride. vi) For this purpose cathode and anode are separated by a steel gauze. ============================================================ Visit www.eservicespakistan.com for Notes, Syllabus, Old Papers, Home Tuitions, Jobs & much more (Page 3 of 6)

Written by: - SHAHZAD IFTIKHAR # 0313-7891989, 0333-5319544 e-mail: [email protected] website: www.eservicespakistan.com CHEMISTRY FOR 9TH CLASS (UNIT # 8) ============================================================

Reaction at Cathode: 2Cl----------------> Cl2 + 2eReaction at Anode: 2Na+ + 2e- ----------------> 2Na Question: Describe the laws of Faraday regarding Electrolysis? Faradays First law of Electrolysis: i) The mass of an element, which is deposited, on an electrode during electrolysis, is directly proportional to the quantity of electricity Q, which es through the electrolyte. ii) The unit of the quantity of electricity is called coulomb. One coulomb is the quantity of electricity ed when one ampere current es for one second. One Faraday = 96,500 coulombs. And Q = Ixt I is the current, t is time in seconds and Q is the quantity of electricity ing through electrolyte. iii) According to this law: m Ixt m = ZxIxt Z is constant and m is mass of substance deposited. Here m is expressed in grams. iv) The quantity of substance, which is deposited when one Faraday of electricity is ed through an electrolyte, is called One Gram Chemical Equivalent of that substance. Faradays Second law of Electrolysis: i) When the same quantity of electricity is ed, for the same time, through different electrolytes connected in series, the substances deposited at the electrodes will be in the ratio of their chemical equivalents. ii) Faraday’s laws are very useful for determination of electrochemical equivalents of different substances. The following equation is used for this purpose. Electrochemical Equivalent (Z) = Quantity of Substance Deposited (W) Quantity of electricity ed (Q) Z = W/Q. Question: Explain Electrochemical Series? i) When an aqueous solution containing Copper and Zinc ions is electrolyzed, zinc ions will remain in the solution while copper ions are reduced and discharged. ii) Cations (positive ions) can be arranged in the order of increasing ease of discharge at the cathode similarly anions (negative ions) can also be arranged in the order of increasing ease of discharge at the cathode. iii) The list of ions arranged in the order of their ease of discharge at the electrodes is called electrochemical series. ============================================================ Visit www.eservicespakistan.com for Notes, Syllabus, Old Papers, Home Tuitions, Jobs & much more (Page 4 of 6)

Written by: - SHAHZAD IFTIKHAR # 0313-7891989, 0333-5319544 e-mail: [email protected] website: www.eservicespakistan.com CHEMISTRY FOR 9TH CLASS (UNIT # 8) ============================================================

iv)

Electrochemical series also throw light on the reactivity of metals, which form ions in aqueous solutions.

Question: Define Electroplating and describe its objectives? It is the process in which a metal is deposited on another metal electrolytically. There are three main objectives of electroplating: Decoration: We deposit noble metals (like Gold & Silver) on inferior metals to enhance their beauty. Protection: Electroplating protect the inferior metals from rusting and reaction of organic salts. Repair: To weld the broken parts of the machinery by electro-deposition of metals. Question: Describe the Procedure of Electroplating? i) The article to be electroplated is first cleaned with sand and then washed with caustic soda solution and then with plenty of water. ii) This article is then made a cathode, while the metal to be deposited is made anode. iii) The electrolyte is a salt of the metal being deposited and the electroplating is carried out in a tank made of cement, glass or wood. It is called electrolytic tank. iv) The electrolyte chosen should have following properties: a. Very soluble in water. b. Good conductor c. Not easily oxidized or reduced or hydrolyzed. d. Cheap. v) Electrodes are dipped in the electrolytic tank and current is ed through it. vi) A thin layer of the noble metal is deposited on the article to be electroplated. vii) The following conditions should be fulfilled to get good deposits. a. High current density. b. Low temperature. c. Higher concentration of the metal in its electrolyte. Question: What is difference between Chemical Reaction and Electrochemical Reaction? The chemical changes taking place in the substance is called chemical reaction. Electrochemical reactions are always oxidation-reduction reaction. Transfer of electrons takes place through the external circuit. Question: Differentiate between the following? Gram equivalent and electrochemical equivalent: Equivalent weight of substance expressed in gram is called gram equivalent. While Electrochemical equivalent is the amount of a substance produced at the electrode when one coulomb of electric current is ed through electrolyte for one second. Electrolytic dissociation and thermal dissociation: ============================================================ Visit www.eservicespakistan.com for Notes, Syllabus, Old Papers, Home Tuitions, Jobs & much more (Page 5 of 6)

Written by: - SHAHZAD IFTIKHAR # 0313-7891989, 0333-5319544 e-mail: [email protected] website: www.eservicespakistan.com CHEMISTRY FOR 9TH CLASS (UNIT # 8) ============================================================

Decomposition of a substance into its ions by electric current is called electrolytic dissociation. Decomposition of a substance into its ions by heating in the absence of air is called thermal dissociation. Question: Why Gold, Silver and platinum are used for making ornaments? They are used to make ornaments because i) They do not rust. ii) They are lustrous. iii) They are not oxidized by environment. iv) They are hard and elastic and can be moulded to any shape. Question: What happens when electricity is ed through a solution? The ions of electrolyte migrate towards respective electrode. Question: Define Electrolytic Cell and Voltaic Cell? Electrolytic Cell: - In this cell a non-spontaneous oxidation-reduction reaction takes place with the help of electrical energy. Voltaic Cell: - In this cell a spontaneous oxidation-reduction reaction is used to produce electric current.

=*=*=*=*= More works/Tasks: Do Exercise from your Book. Do Objectives from book & from any other objective book. Do Numerical with the help of your teacher. Do Interesting Information from book. Do Scientific Reasons with the help of teacher.

============================================================ Visit www.eservicespakistan.com for Notes, Syllabus, Old Papers, Home Tuitions, Jobs & much more (Page 6 of 6)