Monday, May 4, 2020
Metals and Non Metals free essay sample
Appearance and Hardness of materials Object /Material Appearance Hardness (Shiny/Dull) (Very hard/ Not very hard) similar change if we try to beat a wood log ? Let us find out. Activity 4. 1 Take a small iron nail, a coal piece, a piece of thick aluminium wire and a pencil lead. Beat the iron nail with a hammer (Fig. 4. 1). (But take care that you donÃ¢â¬â¢t hurt yourself in the process). Try to hit hard. Hit hard Beating an iron nail with hammer Can you name the materials which are metals? The rest of the materials in Table 4. 1 are non-metals. Metals can be distinguished from non-metals on the basis of their physical and chemical properties. Recall that lustre and hardness are physical properties. also the aluminium wire. Then repeat the same kind of treatment on the coal piece and pencil lead. Record your observations in Table 4. 2. Table 4. 2 Malleability of Materials Object/ Material Iron nail Coal piece Aluminium wire Pencil lead Change in Shape (Flattens/Breaks into pieces) 4. Physical Properties of Metals and Non-metals Have you ever seen a blacksmith beating an iron piece or an article made up of iron, like a spade, a shovel, an axe? Do you find a change in the shape of these articles on beating? Would you expect a You saw that the shape of the iron nail and the aluminium wire changed on beating. If they were beaten harder these could be changed into sheets. You might be familiar with silver foil used for decorating sweets. You must also be familiar with the aluminium foil used for wrapping food. The property of metals by which they can be beaten into thin sheets is called malleability. This is a characteristic property of metals. As you must have noticed, materials like coal and pencil lead do not show this property. Can we call these as metals? Can you hold a hot metallic pan which is without a plastic or a wooden handle and not get hurt? Perhaps not! Why? Try to list some other experiences in which a wooden or plastic handle protects you from being hurt while handling hot things. On the basis of these experiences what can you say about the conduction of heat by wood and plastic? You must have seen an electrician using his screw driver. What kind of handle does it have? Why? Let us find out. the activity with various objects in Class VI. Now, repeat the activity with the materials mentioned in Table 4. 3. Observe and group these materials into good conductors and poor conductors. Table 4. 3 : Electrical conductivity of materials S. No. Materials Good Conductor / Poor Conductor 1. 2. 3. 4. Iron rod/nail Sulphur Coal piece Copper wire You observe that iron rod, nail and copper wire are good conductors while rolled sulphur piece and coal piece are poor conductors. Recall how to make an electric circuit to test whether electricity can pass through an object or not (Fig. . 2). You might have performed Oh! The meaning of recalling our experiences and then of this activity was to show that metals are good conductors of heat and electricity. We learnt this in Class VI. Where do you find the use of aluminium and copper wires? Have you seen wires of coal? Definitely not! The property of metal by which it can be drawn into wires is called ductility. Have you ever noticed the difference in sound on dropping an iron sheet/ plate, a metal coin, and a piece of coal on the floor? If not, you can try it now. Do you note any difference in the sound produced? 45 Have you seen wooden bells in temples? Can you give reason? The things made of metals produce ringing sound when struck hard. Suppose you have two boxes similar in appearance, one made of wood and the other of metal. Can you tell which box is made of metal by striking both the boxes? Since metals produce ringing sounds, they are said to be sonorous. The materials other than metals are not sonorous. After performing the above activities, we can say that some materials are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity. The materials which generally posses these properties are called metals. The examples of metals are iron, copper, aluminium, calcium, magnesium, etc. In contrast, materials like coal and sulphur are soft and dull in appearance. They break down into powdery mass on tapping with hammer. They are not sonorous and are poor conductors of heat and electricity. These materials are called non-metals. The examples of non-metals are sulphur, carbon, oxygen, phosphorus, etc. Metals like sodium and potassium are soft and can be cut with a knife. Mercury is the only metal which is found in liquid state at room temperature. These are exceptions. which rust is formed. You had also performed in Class VII an activity of burning a magnesium ribbon in air. You had learnt that in both the processes oxide formation takes place. Complete the following reactions of iron and magnesium with oxygen. Iron (Fe) + Oxygen (O2) + Water (H2O) ? Magnesium (Mg) + Oxygen (O2) ? Activity 4. 3 Let us check the nature of rust formed as a result of the reaction between iron, oxygen and water. Collect a spoonful of rust and dissolve it in a very little amount of water. You will find that the rust remains suspended in water. Shake the suspension well. Test the solution with red and blue litmus papers (Fig. 4. 3). What do you observe? Is the solution acidic or basic? Rust suspension Red litmus paper 4. 2 Chemical Properties of Metals and Non-metals A. Reaction with Oxygen You are familiar with the phenomenon of rusting of iron. Recall the reaction by 46 Rust Fig. 4. 3 : Testing the nature of rust SCIENCE Does copper also get rusted? I have seen a greenish deposit on the surface of copper vessels. When a copper vessel is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of copper hydroxide (Cu(OH) 2 ) and copper carbonate (CuCO3). The following is the reaction 2Cu+H2O+CO2+O2Cu (OH)2 + CuCO3 moist air As soon as sulphur starts burning, introduce the spoon into a gas jar/ glass tumbler [Fig. 4. 4 (a)]. Cover the tumbler with a lid to ensure that the gas produced does not escape. Remove the spoon after some time. Add a small quantity of water into the tumbler and quickly replace the lid. Shake the tumbler well. Check the solution with red and blue litmus papers [Fig. 4. 4 (b)]. Now recall the activity of burning magnesium ribbon. The ash obtained on burning magnesium ribbon is dissolved in water and tested for its acidic / basic nature. Is the solution acidic or basic? How do you ascertain this? You must have observed that the red litmus turns blue. So, oxide of magnesium is also basic in nature. In general, metallic oxides are basic in nature. Let us now observe the reaction of non-metals with oxygen. Improvised deflagrating spoon Fig. 4. 4 (a) : Burning of sulphur powder Activity 4. 4 (To be demonstrated by the teacher in the class) Take a small amount of powdered sulphur in a deflagrating spoon and heat it. If deflagrating spoon is not available, you may take a metallic cap of any bottle and wrap a metallic wire around it and give it the shape shown. Testing of solution with litmus papers 47 Table 4. 4 : Metals and Non-metals in Acids and Bases S. No. 1. 2. 3. 4. 5. Name of the base Calcium hydroxide Metal Calcium Name of the acid Sulphuric acid Non-metal Sulphur The name of the product formed in the reaction of sulphur and oxygen is sulphur dioxide gas. When sulphur dioxide is dissolved in water sulphurous acid is formed. The reaction can be given as follows: Sulphur dioxide (SO2) + Water (H2O) Sulphurous acid (H2SO3) The sulphurous acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature. Recall the name of some of the laboratory acids and bases you have read in Class VII. Note down their names in Table 4. 4. Identify the metal or nonmetal present in them which forms oxides with oxygen. B. Reaction with Water Let us see how metals and non-metals react with water. Sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. It is, therefore, stored in kerosene. 48 Activity 4. 5 To be demonstrated by the teacher. During demonstration special care should be taken that the size of the sodium metal piece is roughly the size of a wheat grain. It should be held with a pair of tongs. ) Take a 250 mL beaker/glass tumbler. Fill half of it with water. Now carefully cut a small piece of sodium metal. Dry it using filter paper and wrap it in a small piece of cotton. Put the sodium piece wrapped in cotton into the beaker. Observe carefully. During observation keep away from the beaker. When reaction stops touch the beaker. What do you feel? Has the beaker become hot? Test the solution with red and blue litmus papers. Is the solution acidic or basic? Fig. 4. 5 : Reaction of sodium with water SCIENCE You observed that sodium reacts vigorously with water. Some other metals do not do so. For example, iron reacts with water slowly. Generally, non-metals do not react with water though they may be very reactive in air. Such non-metals are stored in water. For example, phosphorus is a very reactive non-metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water. C. Reactions with Acids Let us see how metals and non-metals behave with acids. test tubes and label them as A, B, C, D, E, and F. With the help of a dropper add 5 mL of dilute hydrochloric acid to each test tube one by one. Observe the reactions carefully. If no reaction occurs in a cold solution, warm the test tube gently. Bring a burning matchstick near the mouth of each test tube. Repeat the same activity using dilute sulphuric acid instead of the dilute hydrocholoric acid. Record your observations in Table 4. 5. Is there a difference in the way metals and non-metals react with acids? What could the Ã¢â¬ËpopÃ¢â¬â¢ sound in some cases be due to when a burning match stick is brought near the mouth of the test tubes? You must have found that nonmetals generally do not react with acids but metals react with acids and produce hydrogen gas that burns with a Ã¢â¬ËpopÃ¢â¬â¢ sound.