202110241-TRIUMPH-STUDENT-WORKBOOK-PHYSICAL_SCIENCE-G08-PART1

Observation: Liquid LED glows Good conductor or (Yes/No) poor/bad conductor S.No. 1. Distilled water No Bad conductor 2. 3. Drinking water Yes Good conductor 4. 5. Coconut oil No Bad conductor 6. 7. Lemon juice Yes Good conductor 8. 9. Vinegar Yes Good conductor 10. Kerosene No Bad conductor Vegetable oil No Bad conductor Sugar solution No Bad conductor Common salt Yes Good conductor solution Pure milk No Bad conductor Conclusion : We conclude that when the liquid between the two pins of the tester allows electric current to pass through, the circuit is completed (Closed) and the LED glows. Then we say, the liquid is a good conductor. On the other hand, when the liquid does not allow the current to pass through, the circuit is incomplete (Open) and the LED does not glow. Then we say the liquid is a bad conductor. Q2. [AS3] Conduct an experiment for testing the electric conductivity of electrolytes. [Refer to TB page 130 Q3] A. Aim : To test electric conductivity of electrolytes. Materials required: Distilled water, tester, copper sulphate, lemon juice, common salt. SESSION 1. INTRODUCTION AND ELECTRICAL CONDUCTIVITY OF LIQ... 249

i. Take some amount of distilled water in three different containers. ii. Dissolve small quantity of common salt in the water of first container. iii. Dissolve the copper sulphate, lemon juice in second and third container respec- tively. iv. Use the tester that we used in activity 2, and repeat the activity. v. Note the observations in a table. Observation: Does the S.No. Material LED Good conductor or 1 Distilled water poor/bad conductor glow? (Yes / No) No Bad conductor 2 Distilled water + salt Yes Good conductor 3 Distilled Yes Good conductor water + CuSO4 Yes Good conductor 4 Distilled water + lemon juice Conclusion : Distilled water does not allow electric current to pass. Water in its pure form is a bad conductor of electricity. But when water contains salts or acids, it allows the passage of electric current and turns into a good conductor of electricity. From the above activities we can conclude that solutions like acids, bases or salts conduct electricity. Objective Questions (1) Pure water is a .(Pg 130:TB Q 2) (A) Electric conductor (B) Semi conductor (C) Insulator (D) Resistor Correct Answer: C SESSION 1. INTRODUCTION AND ELECTRICAL CONDUCTIVITY OF LIQ... 250

(2) The material which does not allow electric current to pass through it is known as . (Pg130:TB Q 3) (A) Electric conductor (B) Insulator (C)Electric resistance (D)Semi conductor Correct Answer: B SESSION 1. INTRODUCTION AND ELECTRICAL CONDUCTIVITY OF LIQ... 251

SESSION 2 CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 2.1 Mind Map 1. Electrolytic cell 2. Electroplating – SESSION 2. CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 252

2. Electroplating 2.2 Terminology (i) Distilled Water – Distilled water is water that has many of its impurities removed through distillation. It is used in science laboratories for various purpose. (ii) LED – A Light Emitting Diode is a semiconductor device that emits visible light when an electric current passes through it. (iii) Positive Terminal – In a source of electrical energy, such as a battery, cell, or generator, the terminal to which electrons flow. 2.3 Key Concepts i. Most of the liquids which conduct electricity are solutions of acids, bases and salts. ii. The passage of current through a liquid causes chemical reactions. iii. Electrolyte is a solution of substances through which electric current can pass. iv. Electrolysis is the process of breaking up of an electrolyte chemically by passing electricity through it. v. Electroplating is the coating of a thin layer of metal on another metal by the process of electrolysis. vi. A conductor through which electricity enters or leaves an object, substance, or region. 2.4 Reflection on Concepts Q1. [AS5] Draw the diagram of Electrolytic cell and explain. [Refer to TB page 129 Q4] SESSION 2. CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 253

A. An electrolytic cell is a cell which requires an outside electrical source to initiate the redox reaction. An electrolytic cell consumes electrical energy from an external source, using it to cause a non-spontaneous redox reaction to occur. The process of how electric energy drives the non-spontaneous reaction is called electrolysis. An electrolytic cell contains two electrodes which are solid metals connected to an external circuit that provides an electrical connection between the two parts of the system. The electrolytic cell usses electron movement (in the source of electricity) to cause the redox reaction. In an electrolytic cell, electrons are forced to flow in the opposite direction. The oxidation half–reaction occurs at one electrode (the anode), and the reduction half–reaction occurs at the other (the cathode). When the circuit is closed, electrons flow from the anode to the cathode. The electrodes are also connected by an electrolyte, an ionic substance or solution that allows ions to transfer between the electrode compartments, thereby maintaining the system’s electrical neutrality. Oxidation half–reaction : Z - → Z + e- Reduction half reaction : Y+ + e- → Y Over all cell reaction: Y+ + Z - → Y+ Z ( G>0) 2.5 Application of Concepts Q1. [AS1] Which energy is a cause for glowing of bulb in an electrolytic cell? [Refer to TB page 130 Q1] A. Chemical energy SESSION 2. CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 254

Q2. [AS5] Make a battery from four lemons and test it with an LED in the circuit. [Refer to TB page 130 Q4] A. MATERIALS REQUIRED: 4 lemons, 4 pieces of copper wire, 4 paper clips, 4 zinc plated nails, 4 wires and LED. i. Place a nail and a piece of copper into each lemon. ii. The copper acts as a positive terminal and nail as a negative terminal. iii. Join the 4 lemons using wire and clips such that nail of the first lemon is connected to copper of the second lemon and so on. iv. Add wires and clips to the first piece of copper and last piece of nail. v. Join one end of the leg of LED to wire of the first lemon and second leg of LED to the wire of the last lemon. vi. You will observe the dim glow of the light. 2.6 Higher Order Thinking Skills Q1. [AS1] Is plastic coated by the process of electroplating? Why? [Refer to TB page 130 Q2] A. Plastic is a poor conductor of electricity, and is a polymer and a covalent substance and cannot be decomposed into ions. Hence plastic cannot be coated on metal by the process of electroplating. Q2. [AS3] If the key is to be coated with aluminium instead of copper, what changes do we need to make in the experiment of coating on iron key with copper? [Refer to TB page 130 Q1] A. We have to use electrolyte like aluminium nitrate. Note –Aluminium cannot be produced by the electrolysis of an aluminium salt dissolved in water because of the high reactivity of aluminium with the protons of water and the subsequent formation of hydrogen. As in aqueous solution, protons (H+ ) are prefer- entially reduced before Al3+ ions, leading to hydrogen evolution, the reduction of Al3+ requires to perform the electrolysis in a molten aluminium salt in the absence of water. SESSION 2. CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 255

2.7 Suggested Experiments Q1. [AS3] Conduct an experiment for coating on iron key with copper by electroplating method and prepare a note. [Refer to TB page 130 Q1] A. AIM: Coating an iron key with copper by electroplating method. MATERIALS REQUIRED: Copper plate, crystals of copper sulphate, an iron key, glass beaker, water, sulphuric acid, battery cell, and connecting wires. PROCEDURE: i. Dissolve copper sulphate crystals in water to prepare a concentrated solution and pour it in a beaker. ii. Add a few drops of dilute sulphuric acid to it. iii. Tie one end of copper wire to an iron key. Connect the other end to negative termi- nal of a battery. iv. Suspend the key and copper plate into the copper sulphate solution through posi- tive terminal of a battery through a switch. v. Care should be taken that the key and the copper plate should not touch each other. vi. Put on the switch for about 10– 15 minutes.Copper gets deposited on the iron key. When electric current is passed through the copper sulphate solution, in which the cop- per sulphate is present in the form of copper and sulphate ions, the free copper ions are drawn to the electrode connected to the negative terminal of the battery and deposited on it. SESSION 2. CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 256

Thus one metal is coated with another material. This process is known as electroplating. 2.8 Suggested Projects Q1. [AS4] Collect the information from various sources on the applications of electroplating in daily life and prepare a note on that. [Refer to TB page 130 Q1] A. Students’ activity. Few examples are given – i. Chromium plating is done on different parts of vehicles to give them lustre. ii. A fine layer of gold is deposited on cheap metals. iii. Iron used in construction is coated with a layer of zinc to protect it from corrosion and rusting. iv. Electroplating is also used in repairing worn out parts of machinery. Q2. [AS4] In many of the activities in this chapter, we have used a tester made up of LED. Can we avoid LED and use something else as a tester? Collect the information and make a model. [Refer to TB page 130 Q2] A. Magnetic compass needle could be an alternative tester. We know that when we take a current carrying wire near a magnetic compass, it deflects. This property is used to make a tester using a magnetic compass needle. Objective Questions (1) One of the following is not an electrolyte – (Pg 130: TB Q 5) (A) Sulphuric acid (B) Lemon juice (C)Tamarind juice (D)Pure distilled water Correct Answer: D .(Pg 130;TB Q 4) (2) Electroplating is possible through (B) Chemical process (D) Filtration (A) Electrolysis (C) Dissolving Correct Answer: A SESSION 2. CHEMICAL EFFECTS OF ELECTRIC CURRENT AND ITS USES 257

(3) Which of the following is also used in ornamentation and decoration? ( Pg 130: TB Q 1) (A) Electro typing (B) Electroplating (C) Electroprinting (D) Galvanizing Correct Answer: B —— CCE Based Practice Questions —— AS1-Conceptual Understanding Very Short Answer Type Questions [Refer to Session 9.1 ] 1. State true or false. (i) All materials conduct electricity equally. [] (ii) Distilled water is a good conductor of electricity. [] (iii) Distilled water which is a poor conductor of electricity, can be transformed into a good conductor of electricity. [] 2. Fill in the blanks. [Refer to Session 9.1 ] (i) We mostly get electric shocks with hands. (ii) The materials which allow electric current to pass through them are called of electricity. 3. State true or false. [Refer to Session 9.2 ] CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 258

(i) A greenish blue spot is seen on the potato around the wire connected to the negative terminal of the battery. [] (ii) Dilute sulphuric acid is an electrolyte. [] 4. Answer the following questions in one sentence. [Refer to Session 9.2 ] (i) Give one use of electroplating. (ii) From the name of which famous scientist is the electrical term “voltage” derived? (iii) In electrolysis, which form of energy is chemical energy converted to? 5. Fill in the blanks. and plates 259 [Refer to Session 9.2 ] (i) Alessandro Volta made his first cell using dipped in sulphuric acid. CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS

(ii) In electroplating, an metal is coated with a metal. Short Answer Type Questions 6. Answer the following questions in 3-4 sentences. (i) [(Session 9.1)] What are good conductors of electricity? (ii) [(Session 9.1)] Define electric conductivity. AS2-Asking questions and making hypothesis Short Answer Type Questions CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 260

7. Answer the following questions in 3-4 sentences. (i) [(Session 9.1)] Swathi has two materials in her hand. One is copper wire and other one is cotton thread. She wants to make a complete circuit. Which one of the above mentioned materials she is going to use to glow the bulb in the circuit and why? AS3-Experimentation and field investigation Short Answer Type Questions 8. Answer the following questions in 3-4 sentences. (i) [(Session 9.1)] Write an experiment to prove that normal water is a good conductor of electricity but distilled water is not. CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 261

Long Answer Type Questions 9. Answer the following questions in 6-8 sentences. (i) [(Session 9.1)] What is the procedure to check if a given liquid is a good conductor or a bad conductor of electricity? CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 262

AS4-Information skills and projects Long Answer Type Questions 10. Answer the following questions in 6-8 sentences. (i) [(Session 9.1)] Collect information about different liquids which are used in our daily life. Prepare a table and classify them as good conductors and bad conductors of electricity. CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 263

AS5-Communication through drawing and model making Short Answer Type Questions 11. Answer the following question. (i) [(Session 9.2)] Draw an experimental set up for the coating of iron key with copper by electroplating method. AS6-Appreciation and aesthetic sense, Values Long Answer Type Questions 12. Answer the following questions in 6-8 sentences. (i) [(Session 9.2)] Write a note on Luigi Galvani’s contribution to the field of electricity. CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 264

AS7-Application to daily life, concern to bio diversity Short Answer Type Questions 13. Answer the following questions in 3-4 sentences. (i) [(Session 9.2)] Give some examples for the electroplated objects that we see in our daily life. CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 265

Objective Questions AS1-Conceptual Understanding 14. Choose the correct answer. (i) Which of the following liquid would conduct electricity? (A) Vegetable oil (B) Lemon juice (C)Distilled water (D) Honey (ii) Why do we use LED in the tester instead of bulb? (A) Because the LED glows only when the current is strong (B) Beacuse the LED costs lesser than the bulb (C)Because the LED glows even when the current is very weak (D)Because the LED is costlier than the bulb AS2-Asking questions and making hypothesis 15. Choose the correct answer. (i) Distilled water does not conduct electricity. What substance can be added to distilled water in small amounts to make it a good conductor of electricity? (A) Salt (B) Coconut oil (C) Alcohol (D)All of the above AS3-Experimentation and field investigation 16. Choose the correct answer. (i) Electrolysis is the process of conversion of (A) electric energy to chemical energy (B) chemical energy to light energy CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 266

(C)electric energy to light energy (D)chemical energy to electric energy (ii) A tester is used to check the conduction of electricity through two liquids, labeled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that (A) liquid A is a better conductor than liquid B (B) liquid B is a better conductor than liquid A (C)both liquids are equally conducting (D)conducting properties of liquids cannot be compared in this manner AS4-Information skills and projects 17. Choose the correct answer. (i) Following are some points to be remembered when electroplating a metal. Which of the following is an incorrect point? (A) The object to be electroplated should be free from greasy matter (B) The surface of the article should be smooth (C)The concentration of the electrolyte should be adjusted as to get smooth coating (D)Current must be same throughout AS5-Communication through drawing and model making 18. Choose the correct answer. (i) In the following picture. The zinc and copper rods are called CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 267

(A) electrolyte (B) electrodes (C) electrolysis (D) electroplating AS6-Appreciation and aesthetic sense, Values 19. Choose the correct answer. (i) Which metal is electroplated on iron for making cans used for storing food? (A) Tin (B) Copper (C) Zinc (D) Aluminium (ii) Which properties of chromium metal make it suitable for electroplating it on ma- chinery parts? (A) It protects them from corrosion (B) It gives them a good polish (C)It protects them from scratches (D)All of the above AS7-Application to daily life, concern to bio diversity 20. Choose the correct answer. (i) Which of the following options is not a use of electroplating? CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 268

(A) To protect certain metals from corrosion (B) To give a good polish to the metal (C)To repair worn out parts of a machinery (D)To make the metal a good conductor CHAPTER 9. ELECTRICAL CONDUCTIVITY OF LIQUIDS 269

PROJECT BASED QUESTIONS —— Project Based Questions —— (i) Make a report listing the various activities from your daily life where you can see force changing the motion of any objects you are dealing with. (ii) It is evident that objects are given special shapes to reduce friction while moving through fluids. Make a list of those kinds of objects and collect pictures from internet or magazine books and prepare a scrap book. Or Taking help from internet or from library books make a project report on various meth- ods of increasing and decreasing friction with suitable examples from your daily life. (iii) Assume that you are going to publish an article in a local newspaper to spread awareness about environmental pollution caused by usage of plastic. Give a glimpse of your article mentioning all the important points that you are going to cover in your article. Or Prepare a scrap book putting pictures of different types of synthetic fibre and mention- ing their uses in our daily life. (iv) Choose any 10 metals / non metals and make a report on their uses. Also collect pictures of those metals / non metals and paste on your report. Take help from internet or magazines. Or Make a project report by listing all the materials that you use every day since morning till evening showing their extent of conductivity as good or bad for heat. (v) ‘Sometimes the same word is uttered in different ways to express different emotions.’ For example, the word ‘NO’ is uttered in different pitches to express negativity, anger and frustration. Establish that the above statement is true reciting at least 5–10 more examples like word NO in front of the class. Or Make a project report on image formation for plane mirror. (vi) Taking examples from your nearby factories, industries and vehicles on the road, you make a report on harmful effects on the environment due to burning of fossil fuels. Also mention the steps to minimize the effect. (vii) Make a project report on various consequences our future world is going to face be- cause of the rapid uses and misuses of fuels. Also mention few suggestions to avoid such consequences. (viii) Bio–diesel is an alternative fuel source. Make a project report on biodiesel. Include its preparation or formation, countries where it is produced and why it is not prepare in large scale. Project Based Questions 270