Chapter 6 Scientific Experiments PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Six Scientific experiments Introduction...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Six Scientific experiments Introduction LY In Standard Five, you conducted experiments on measuring human body temperature, expansion and contraction of solid materials, liquids and gases. You also conducted experiments on transfer of N heat in solid materials, liquids and air, and on how to reduce heat O loss. When scientific experiments are carried out carefully and accurately, they give correct results which stimulate inquisitive mind, thinking and discovery capacity. In this chapter, you will learn about SE the concept of fire and carrying out experiments on firefighting. You will also learn about acids and bases and carrying out experiments to identify their properties. In addition, you will carry out experiments U to identify conditions necessary for rusting and how to prevent it. The competencies developed will enable you to protect yourself from fire accidents, identify substances with acidic and basic properties, and E keeping iron materials free from rusting. N Fire and firefighting LI Think N O Sources of fire and proper ways of extinguishing fire R The concept of fire FO A fire is a state involving the burning of materials in the presence of oxygen gas which is accompanied by giving out heat and light. For a fire to start, three components are needed, namely oxygen gas, heat, and fuel. 63 SCIENCE AND TECHNOLOGY STD 7.indd 63 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Oxygen gas supports combustion: heat raises the temperature of the combustible material. Fuel is a substance that can be burned to produce heat or power. Fuel can be in solid, liquid or gaseous forms. The interactions of oxygen gas, heat and fuel form a fire triangle as shown in Figure 1. Thus, if one component is LY missing, fire cannot start. Figure 1: Fire triangle Fire is essential in the daily life of human beings. However, fire is very N dangerous in case it cannot be controlled. O Various factors can cause fire accidents. These include the following: (a) Cigarette smoking and improper disposal of cigarette butts; (b) Electrical faults; (c) Lightning; SE U (d) Children playing with lighting matches; (e) Friction due to lack of lubricants, as in vehicles; (f) Burning of forest; E (g) Uncontrolled burning of waste; N (h) Clearing fields or farms using fire; (i) Carelessness in using candles, matches, or stoves which use LI kerosene, gas, charcoal, or electricity; and N (j) Carelessness during welding. In the event of fire, remove one of the components shown in the fire O triangle to extinguish the fire. R Classes of fire There are various classes of fire based on the burning materials. These FO classes are A, B, C, D and F. Each class of fire has appropriate firefighting techniques as explained in the following sections: 64 SCIENCE AND TECHNOLOGY STD 7.indd 64 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Class A fire Fire in this category is caused by the burning of solid materials such as wood, paper, clothes, plastic, mattresses and grass. This type of fire is extinguished by water, dry sand or a fire blanket, as presented in Figure 2. LY (a) Bucket of water (b) Bucket of dry sand (c) Fire blanket N Figure 2: Equipment for extinguishing Class A fire O Class B fire Fire in this category is caused by explosive and flammable liquids such as petrol, diesel, kerosene, and oil based paints. If this type of fire is in SE a small extent, it can be extinguished using dry sand or a fire blanket. Water cannot be used to extinguish Class B fire because it spreads the flammable substance like oil that increases the extent of the fire. This U fire can also be extinguished using carbon dioxide gas which is stored in a special cylinder with a black sign. In addition, dry powder stored in a special cylinder with a blue sign is also used to extinguish this type of fire. Figure 3 shows labelled carbon dioxide gas and dry powder fire E extinguishing cylinders. N Safety pin Safety pin Release LI Release Discharge lever lever Discharge hose hose Carrying N handle Discharge Carrying horn handle O R Discharge nozzle FO (a) Carbon dioxide gas cylinder (b) Dry powder cylinder Figure 3: Cylinders containing fire extinguishing chemicals 65 SCIENCE AND TECHNOLOGY STD 7.indd 65 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Class C fire Fire in this category is caused by the burning of flammable gases such as butane, propane, methane, and acetylene. Water is not used to extinguish gas fire, but it can be used to cool the gas cylinder to prevent it from explosion. This type of fire is extinguished using carbon dioxide gas or dry powder shown in Figure 3. Closing the gas pipe or cylinder valve is an alternative way of extinguishing the fire caused by gas. LY Class D fire Fire in this category is caused by combustible metals such as magnesium, potassium, and iron. This type of fire is extinguished using dry powder. N Water is not used to extinguish Class D fire. Also, it is not advised to O extinguish Class D fire using carbon dioxide gas. Class F fire SE Class F fire involves cooking oil. This type of fire is extinguished using carbon dioxide gas or dry powder. U Fire caused by electrical faults Electricity is not among the classes of fire, but it can be a source of any of E the fire Classes A, B, C, D and F. Normally, the fire caused by an electrical fault is extinguished based on the burning material. Thus, dry powder, N carbon dioxide gas or dry sand can be used to extinguish this fire. Before LI extinguishing the fire caused by an electrical fault, the main electrical switch should be turned off. It is not advised to use water before turning N off the main switch. This is because water conducts electricity. Thus, one may get an electrical shock. If the main switch cannot be turned off, it is O recommended to use fire extinguishers which do not conduct electricity such as dry sand, dry powder, and carbon dioxide gas. R Procedure for firefighting FO The following are the steps to be followed in firefighting using carbon dioxide gas or dry powder, as shown in Figure 4. 66 SCIENCE AND TECHNOLOGY STD 7.indd 66 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 1. Remove the safety pin. 2. Hold the discharge hose of the carbon dioxide gas or dry powder and target LY at the base of the fire. N O 3. Squeeze the top lever to release the SE 4. Sweep from side to side until the fire extinguishing agent. is extinguished. U Figure 4: Steps for using carbon dioxide gas or dry powder fire extinguisher Note: Dry sand, water, fire blanket and fire extinguishers containing E chemicals, are used to extinguish fire at the initial stages. At a fully N developed stage, the fire will be extinguished by the firefighters who use special equipment such as a fire tender as shown in Figure 5. LI N O R FO Figure 5: Firefighters extinguishing fire 67 SCIENCE AND TECHNOLOGY STD 7.indd 67 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Factors to be considered during firefighting 1. The Class A fire is not extinguished using carbon dioxide gas because of the following reasons: (a) It can be expelled by wind and thus blocked from reaching the base of the fire. (b) It removes oxygen gas temporarily which then returns to restart the fire. (c) It is not capable of lowering the temperature of the burning solid LY substances. 2. Before extinguishing the fire caused by an electrical fault, switch off the main switch. N 3. Use the appropriate firefighting equipment for the relevant class of O fire. 4. It is important to make firebreaks around fields and forests. 5. SE It is important for buildings to have fire extinguishers and lightning conductors. 6. In the event of fire in your area, observe important things to save U lives and properties. These are to scream, ring a bell, or press the fire alarm. Also, call the Fire and Rescue Force immediately on phone number 114. Try to extinguish the fire using the available fire E extinguishers without endangering your life and that of others. N Experiment 1: To examine whether a Class A fire can be extinguished LI by water Aim: N To extinguish a Class A fire using water Materials: pieces of paper, a match box and a bucket of water O Caution: Fire is dangerous. Be careful when carrying out this experiment to avoid any potential harm. Make sure that the experimental R area is not too close to combustible materials such as dry grasses to prevent fire from spreading elsewhere. FO Procedure 1. Take a bucket full of water to a designated area for the experiment. 2. Take a match then burn the papers. What has happened? 68 SCIENCE AND TECHNOLOGY STD 7.indd 68 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 3. Take a bucket of water. Then, pour the water on the burning papers. Results: What happened after pouring the water on the fire? Conclusion: Write the conclusion of the experiment. Experiment 2: To examine whether a Class B fire can be extinguished by dry sand LY Aim: To extinguish a Class B fire using dry sand. Materials: one litre of kerosene mixed with a quarter litre of diesel, a bucket with dry sand, aluminium dish, water and a match N box O Caution: Fire and the materials used in this experiment are dangerous. Kerosene and diesel are flammable. Be careful to avoid health problems or effects to the environment. Use special Procedure protective equipment. SE 1. Fill the aluminium dish with dry sand. Then, pour water into the dish U containing sand until the sand is wet. 2. Pour kerosene mixed with diesel into the aluminium dish with the wet sand. E 3. Take a match, then light a fire in the dish. What has happened? 4. Take dry sand from the bucket. Then, pour over the fire. Find out N what happens. LI Results: What happened after pouring the sand on the fire? Conclusion: Write the conclusion of the experiment. N O Exercise 1 Answer the following questions: R 1. Name the firefighting equipment used to extinguish the following classes of fire: FO (a) Class A _________ (b) Class B _________ (c) Class C _________ 69 SCIENCE AND TECHNOLOGY STD 7.indd 69 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. Mention three components for a fire to start. 3. Why is water not used to extinguish the fire caused by petrol or kerosene? Acids and Bases Think LY Distinguishing properties of acids and bases N O The concept of acid An acid is a chemical substance that has the characteristics such as sour taste, changes blue litmus paper to red, and corrosive in a concentrated SE form. There are two main types of acids: natural acids and artificial acids. Examples of natural acids are acetic acid, which is found in vinegar, and lactic acid found in yoghurt. Similarly, in some animals’ digestive U systems, there is a natural acid called hydrochloric acid which helps in digestion. Artificial acids are those which are manufactured in industries. Examples of such acids are nitric acid and sulphuric acid. Acids are used E to manufacture various products such as car batteries liquid, fertilizers, N ink, insecticides, paints, dyes, and detergents. Similarly, acids are used to add flavour to foods. In addition, acids are used in different laboratories LI in schools, colleges and factories for various investigations. N The concept of base O Base is a chemical substance that has the characteristics such as slippery feel, bitter taste, turns red litmus paper blue, and corrosive in a concentrated form. Bases are found in various substances, such as R ashes, soaps, in animals’ bodies and in chemicals for stain removal. They are used in making medicines and other chemicals, and in breaking FO down fats. In addition, bases are used to reduce the amount of acid in the human body and in carrying out laboratory investigations. 70 SCIENCE AND TECHNOLOGY STD 7.indd 70 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Indicators of acids and bases Substances used to detect the presence of acid or base in various liquids are called indicators. Various types of indicators are used in scientific experiments. An example is litmus paper made from coloured flower petals like hibiscus flowers. Some indicators, such as phenolphthalein (POP), are manufactured in industries. LY Activity: To make a litmus paper indicator using flowers Materials: light white plain paper, hibiscus flowers, a pair of scissors, N ruler, two bowls, a knife, a piece of soap, water and lemon Caution: Some of the materials used in this activity are dangerous. Be O careful to avoid harm. Procedure 1. Take the flower petals. SE 2. Place the paper on the table. Then, take the flower petals and rub U them on both sides of the paper. Make sure both sides of the paper are properly coloured. 3. Clean the paper to remove the dirt that might appear. E 4. Cut the paper into small pieces of one centimetre wide and five N centimetre long. 5. Put a soap in the bowl; then, dissolve it using water. LI 6. Put the paper indicator you prepared into the soap solution. What N do you observe? 7. Cut the lemon and squeeze it into another bowl to get juice. O 8. Insert the indicator you prepared into the juice. What do you observe? 9. Let the pieces of paper dry and use them as indicators to identify R acids or bases in liquids in your environment. FO 71 SCIENCE AND TECHNOLOGY STD 7.indd 71 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Experiment 3: To examine the properties of acids Aim: To identify the properties of acidic substances using litmus paper. Materials: lemons, unripe oranges, unripe mangoes, yoghurt, water, knife, blue litmus paper, red litmus paper, filter, test tube or bowl, small crusher or mortar and pestle Caution: Some of the materials used in this experiment such as the LY knife may cause harm. Be careful during the experiment. Procedure 1. Peel lemons, unripe oranges and mangoes to remove their outer N skins. 2. Cut the lemon into small slices and grind them using the small crusher O or mortar and pestle. 3. Add a small amount of water to the ground fruit, filter it to get juice, and put the juice in a bowl or test tube. SE 4. Insert blue litmus paper and red litmus paper into the fruit juice you prepared. What has happened? U 5. Repeat steps 2 to 4 for all the fruits. 6. Put yoghurt in a bowl or test tube. 7. Insert blue litmus paper and red litmus paper into the yoghurt. What E has happened? N Results: Which litmus paper changed its colour in this experiment? What is the colour change? Which litmus paper did not LI change its colour? Conclusion: Acidic substances change the colour of litmus paper N from________ to ________. O Experiment 4: To examine the properties of bases R Aim: To identify the properties of bases using litmus paper and beef fat FO Materials: ashes or dry banana leaves, chalk or lime, gallbladder, beaker, glass or plastic bottle, bowl, beef fat, water, filter or filter paper, and blue litmus paper and red litmus paper 72 SCIENCE AND TECHNOLOGY STD 7.indd 72 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Caution: Some of the substances used in this experiment such as ashes, dry banana leaves, bile, and lime can cause health effects. Be careful and wear protective equipment. Procedure 1. Put the ashes in a beaker and add water to get a solution. 2. Filter the mixture obtained using filter paper. 3. Take bile from the gallbladder and place it in a glass or plastic bottle. LY You can use lime or chalk instead of bile. 4. Dip the red litmus paper and blue litmus paper into a glass filled with N ash solution. What do you observe? 5. Dip the red litmus paper and blue litmus paper into the bile, lime, or O chalk solution. What do you observe? 6. Put beef fat in a bowl. Then, pour the bile, lime, or chalk solution. Results: SE The red litmus paper changed its colour to ________. What happened after the bile was poured into the beef U fat? Conclusion: The bases change the colour of _________ litmus paper to________. Also, they break down beef fat. Thus, in E the animal’s digestive system, bile breaks fat into fatty N acids. LI Exercise 2 N Answer the following questions: O 1. List various items that contain (a) acids. (b) bases. R 2. What are the properties of the acid found in batteries? FO 3. Name five uses of (a) acids. (b) bases. 73 SCIENCE AND TECHNOLOGY STD 7.indd 73 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Explain three properties of (a) acids. (b) bases. 5. How will you know that a tomato is acidic in nature while a piece of soap is basic in nature? Rusting and how to prevent it LY Think Causes of rusting and proper methods of prevention N O The concept of rust SE Rust is a reddish brown coat that occurs on the surfaces of iron materials. For example, nails that have been left out for a long time without proper care develop a reddish brown coat. The coat can be scratched from the nails. Rusted nails differ from those which have been properly stored in a U packet. E Experiment 5: To examine substances which rust and those which do not rust N Aim: To determine that iron substances rust LI Materials: water, iron nails, stainless steel or brass keys, a piece of plastic material, a piece of iron rod, stainless steel or brass N spoons and bowl Caution: Some materials like iron nails and iron rods are dangerous; O they can cause harm and health problems. Be careful when performing the experiment. R Procedure 1. Put water in a bowl. FO 2. Dip iron nails, a piece of iron rod, a piece of plastic material, a stainless steel spoon and stainless steel keys into the water. Leave another set of such materials outside the water. 74 SCIENCE AND TECHNOLOGY STD 7.indd 74 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 3. Take them out of water and leave them in an open area for three days. 4. After the three days, compare the conditions of the materials dipped in water with those which were not dipped in water. Results: What did you observe after the materials had been placed in water and then left in an open area for three days? LY Conclusion: Write the conclusion of the experiment. N Experiment 6: To examine the conditions necessary for rusting O Aim: To determine the conditions necessary for the rusting of iron nails SE Materials: new iron nails, oil or grease, three ‘sufuria’ or 250 mL beakers with water and a source of heat Caution: Iron nails, oil and grease can cause health effects. Be U careful when using them and wear protective equipment. Procedure E 1. Take three beakers of 250 millilitres each and label them A, B and C. Put equal amounts of water of at least 80 millilitres in beakers A N and B. Or take three small ‘sufuria’ and label them A, B and C. Put enough water to cover the nails in ‘sufuria’ A and B. LI 2. Boil the water in each ‘sufuria’ or beakers A and B for 2 to 3 minutes. N Remove the ‘sufuria’ or beakers from the heat source and dip few new iron nails into the ‘sufuria’ or Beaker A. Make sure the iron nails O are completely covered in water. 3. Pour enough oil to cover the entire surface of the water in ‘sufuria’ R or beaker A. Then, place ‘sufuria’ or beaker A aside. See Figure 6. FO 4. Carefully dip few new iron nails into ‘sufuria’ or beaker B so that the nails are completely covered in water. Do not put oil in the beaker or sufuria B. See Figure 6. 75 SCIENCE AND TECHNOLOGY STD 7.indd 75 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 5. Dry ‘sufuria’ or beaker C using a dry cloth. Also dry few new iron nails and place them in a dry cotton swab. Then, dip them in ‘sufuria’ or beaker C. Cover the ‘sufuria’ or beaker C using a dry cover. See Figure 6. 6. Place the ‘sufuria’ or beaker B near ‘sufuria’ or beaker C. 7. Leave the ‘sufuria’ or beakers for three days before doing the observations. LY Top cover N Oil Iron nail Water O Iron nail Iron nail Water Dry cotton A B C SE Figure 6: Identifying conditions necessary for rusting U Results: After three days, carefully check the status of the nails in each ‘sufuria’ or beaker whether they have rusted or not. Then, fill the results of your experiment as shown in Table 1. E Table 1: Conditions of iron nails after three days N Beaker /‘Sufuria’ A Beaker /‘Sufuria’ B Beaker /‘Sufuria’ C LI Questions N 1. What was the purpose of boiling water in ‘sufuria’ or beaker A? O 2. Why was oil used to cover the surface of water in ‘sufuria’ or beaker A in step 3? R 3. Why were the iron nails placed in dry cotton in ‘sufuria’ or beaker C and ‘sufuria’ or beaker C covered? FO 4. Why was the oil not added in ‘sufuria’ or beaker B? Conclusion: Write the conclusion of the experiment. 76 SCIENCE AND TECHNOLOGY STD 7.indd 76 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Experiment 7: To examine whether painting can prevent rust Aim: To identify the methods of preventing rust Materials: Two pieces of iron sheets, lead oxide paint, green, blue or red paint, brush, bucket, empty can, a piece of sandpaper or steel wire Caution: Iron sheets, paints and other materials used in this experiment LY may cause health effects. Be careful and wear protective equipment. Procedure N 1. Rub two pieces of iron sheets with sandpaper or steel wire. 2. Paint lead oxide on one piece of iron sheet. Do not paint the second O piece of iron sheet. 3. Leave for a while until the lead oxide paint dries. SE 4. Put green, blue, or red paint in any available container. 5. Apply the paint mentioned in step 4 to the iron sheet coated with the lead oxide paint. U 6. Keep out the pieces of iron sheets in the open area for three days. Results: (i) Which piece of the iron sheets rusted? E (ii) Which piece of the iron sheets did not rust? N Conclusion: Write the conclusion of the experiment. LI Exercise 3 N Answer all questions in Sections A and B. O Section A Choose the most correct answer and write its letter in the box provided. 1. Which class of fire is caused by the burning of solid substances such R as clothes and papers? (a) Class D FO (b) Class C (c) Class A (d) Class F 77 SCIENCE AND TECHNOLOGY STD 7.indd 77 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. Acid is a chemical substance that changes litmus paper from ________. (a) red to yellow (b) blue to red (c) green to blue (d) red to blue 3. How can rusting of iron materials be prevented? LY (a) placing them in water (b) smearing them with ashes (c) adding oxygen gas N (d) painting them 4. A base has two important properties: O (a) it changes blue litmus paper to red and kills germs. (b) it changes blue litmus paper to red and breaks down body fats. SE (c) it changes red litmus paper to blue and breaks down body fats. (d) it changes blue litmus paper to red and preven diseases. U 5. Which gas is used during firefighting? (a) Carbon dioxide gas (b) Oxygen gas E (c) Hydrogen gas N (d) Nitrogen gas 6. Write TRUE for a correct statement and FALSE for an incorrect LI statement in the space provided. (a) A fire is a state involving the burning of things in the presence N of oxygen gas that is accompanied by giving off heat and light. O __________ (b) Fuel is in the solid state only. __________ (c) Fire caused by liquids such as diesel can be extinguished by R water. __________ FO (d) An acid is a chemical substance that has a sour taste. _________ (e) A base is a chemical substance that has a bitter taste. _________ 78 SCIENCE AND TECHNOLOGY STD 7.indd 78 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Section B 7. Why do some substances rust? 8. Name five rusting and non-rusting substances. 9. Explain the effects of rusting in your environment. Vocabulary Combustion burning of materials in the presence of oxygen gas LY Concentrated liquid present in a high proportion relative to other substances N Firefighting the action or process of extinguishing fire Flammable a substance that can catch fire easily and burn rapidly O Indicator a substance that exhibits different colours in solutions of different acidity or basicity Litmus SE special paper used for testing whether a substance is acidic or basic U Screaming long, loud cries expressing extreme emotion or pain E N LI N O R FO 79 SCIENCE AND TECHNOLOGY STD 7.indd 79 26/07/2021 12:00