Topic: Physical and Chemical Changes Demonstration: Distinguishing between chemical and physical change A physical change does not involve any bond breaking or making and no new chemical is formed, only the state of the chemical is changed; eg. From solid to liquid A chemical change involves the breaking and making of bonds and the formation of a new substance, identified by, e.g;, a change in colour Safety glasses must be worn, handle lead nitrate and potassium iodide with care minimise contact with skin by wearing gloves/ using spatula if possible when handing these chemicals Requirements: Physical Change: Ice Chemical Change: 2 x large test tubes, rubber stopper to fit test tube, 10 g lead nitrate 10 g potassium iodide black background Make sure that both lead nitrate and potassium iodide are in fine powder form, if not; grind-up separately each solid using mortar and pestle, prior to the demonstration. Physical change: Using tongs, transfer some of the ice into a conical flask. Shake the flask to increase the rate of change from solid to liquid. Chemical change: 1. Place about 15g of lead nitrate into one test tube and about 15g of potassium iodide into another test tube then transfer one solid into another. 2. Stopper the test tube and shake vigorously until there is a colour change. Physical Change: Ice changes into liquid i.e; water. Chemical Change: Both lead nitrate and potassium iodide are white solids. Upon mixing, a yellow solid (lead iodide) is produced. A change in colour indicates chemical change rather than physical change. Mixing of two solids to produce chemical reaction is unusual, as normally this reaction is done by mixing lead nitrate solution and potassium iodide solution, however, using solids is more effective as a demonstration. Students will observe that in the first instance there was only physical change since solid H 2 O turned into liquid, whereas in the second example, a new substance with different colour was formed with no white powder remaining, which means that both potassium iodide and lead nitrate have converted to a new substance. Students will be able to distinguish between physical and chemical changes. Students will be able to write balanced equations from observations and include physical states for all reactants and products. Chemical disposal: Solid waste should be disposed of into a special toxic waste bin. Reaction: Pb(NO 3 ) 2 + 2KI PbI 2 + K 2 (NO 3 ) 2 Page 5 of 18
Topic: Chemical Reactions Demonstration: Burning magnesium Characteristics of a chemical change Identification of products of a reaction Balancing chemical equations Safety glasses MUST be worn at all times DO NOT look directly at the light produced by the magnesium Work on a heat-proof mat when using open flames Turn off gas/spirit lamp when not in use. Requirements: safety glasses, heat-proof mat, metal tongs, gas burner/spirit lamp, matches, magnesium ribbon strips, phenolphthalein. take small strips of magnesium and clean off (use sand paper) any oxide layer formed on the magnesium prior to burning. 1. Put spirit lamp on top of the heat-proof mat. Turn on the spirit lamp. 2. Using metal tongs pick up a piece of magnesium ribbon and hold it inside the hottest part of the flame. Wait until the magnesium starts to burn then take it out of the flame. Please make sure you tell students NOT TO look directly at the light produced by the magnesium. 3. Drop the burning magnesium ribbon onto the heat-proof mat. 4. Transfer the burnt magnesium into water, shake the content, heat the content. 5. Add few drops of phenolphthalein in the content. i. The heated magnesium strip produces a bright white light while burning. ii. The magnesium changes from a silver metallic strip to a white powder. iii. iv. The burnt magnesium is magnesium oxide. Magnesium oxide is sparingly insoluble in cold water but fairly soluble on hot water. v. Aqueous solution of magnesium oxide is basic that is why it changes the clour of phenolphthalein from colourless to pink. Mg(s) + O 2 (g) 2MgO(s) MgO(s) + H 2 O(l) Mg(OH) 2 (aq)
Students should be able to convert observations into a chemical equation. Students should be able to balance chemical equation. Students should identify states of matter and include those when writing equation. All solids may be placed into a laboratory bin. Demonstration: Reaction between sodium and water Characteristics of a chemical change Converting observations into chemical equation Identifying products of a reaction Balancing chemical equations Safety glasses MUST be worn at all times MUST use tweezers when handling sodium Take only one piece of sodium at a time out of the paraffin oil Observe from a distance. Do not stand too close while the reaction is taking place Only use small pieces of sodium (no bigger than pea size) Requirements: safety glasses, overhead projector, large glass bowl, water, tweezers, scalpel, ceramic plate, sodium metal in a container with paraffin oil, phenolphthalein indicator Cut three pea-size pieces of sodium metal and place them in paraffin oil in an enclosed container. Half-fill the large glass bowl with water. 1. The bowl of water should be placed on top of the overhead projector. 2. Place about five drops of phenolphthalein indicator into the water. 3. Drop a small piece of sodium metal into water (Figure 1). Figure: Using tweezers drop small piece of sodium metal into water.
A vigorous reaction takes place upon dropping the sodium metal into the water. A pink colour is formed as the metal reacts with the water. A colourless gas is evolved which ignites and small flame is produced (depends on the size of the sodium). Figure: As soon as the sodium is dropped into water, it starts to turn pink, the colour is due to phenolphthalein indicator which turns pink in the presence of hydroxide ions, as the reaction precedes more hydroxide ions are formed and pinker colour appears. 2Na(s) + 2H 2 O(l) 2NaOH(aq) + H 2 (g) Students should gain practice in converting observations from a reaction into a chemical equation. Students should be able to balance chemical equations and identify states of matter. Students should understand the purpose of an indicator in this reaction and hence why the water turns pink once the sodium metal is dropped in. Left over solution should be washed down a laboratory sink with plenty of water. Make sure any leftover unused sodium pieces are returned to the paraffin oil container. DO NOT place ANY sodium pieces (no matter how small) down the sink.
Demonstration: Reacting hydrogen gas with oxygen gas to produce water Characteristics of a chemical change Converting observations into chemical equation Identifying products of a reaction Balancing chemical equations Safety glasses must be worn at all times Tie long hair back Note that this reaction produces a large flame and some smoke. DO NOT do this reaction in a small classroom. Reaction may be done in a lecture theatre with plenty of overhead space or alternatively outdoors away from flammables. Recommend you turn off smoke sensors to avoid an unnecessary evacuation but note location of manual fire alarm and have a fire extinguisher close by in case of a fire Do not fill the balloon up too much with hydrogen as this will lead to a larger explosion. A small size balloon gives just as good as an affect and is safer and not as loud Equipment: safety glasses, few balloons, hydrogen gas, several pieces of string (about 2 m each), a long stick with wax taper, secured to the end, matches Blow up the balloons with hydrogen, gas. If you are using a reaction, between zinc and hydrochloric acid as your source of hydrogen gas, try not to let in any air into the balloon as this may lead to balloon not to explode, rather it will melt and burn. Tie a long piece of string to the end of each balloon. 1. Tie the end of the string around the leg of a chair or table. Make the string as long as possible, without allowing the balloon to touch the ceiling and so that you are able to reach it with the wax taper stick. 2. Light the wax taper. 3. Stand as far away as possible from the balloon and hold out the wax taper until it touches the balloon WARN students of the bang. A very loud bang is heard. A large ball of flame is produced. Inspection of the remains of the balloon show small droplets of water formed inside the balloon Page 9 of 18
2H 2 (g) + O 2 (g) 2H 2 O(l) Students should be able to write a balanced equation from observation and identify states of matter. Students should gain practice in converting observations from a reaction into a chemical equation. Unexploded hydrogen balloons should be leaked out away from sparks. TOPIC: PROPERTIES OF GASES Demonstration: Preparation and properties of oxygen gas Properties of oxygen gas Method used in identification of oxygen gas The role of a catalyst in a reaction Balancing chemical equations Safety glasses MUST be worn at all times Take care when handling glass tubing, particularly when inserting into stoppers or plastic tubing. Do not place a lighted wooden splint inside the O 2 containing test tube Requirements: safety glasses a large plastic container 1 L beaker 3 test tubes a delivery tube with a stopper on one end a clamp and stand spatula 10 ml measuring cylinder wooden splint and matches two rubber stoppers manganese (IV) dioxide 20 ml of 20% hydrogen peroxide Three quarters fill a 1 L beaker with tap water. Fill two test tubes with water. Place a finger over the tube mouth, invert and place the unsealed end under the surface of the water before removing your finger. The test tube should not contain any air. Place the end of the delivery tube into the beaker. Clamp the reaction tube. 1. Do this reaction within the plastic container to contain any spills. 2. Place a small quantity (about a spatula full) of MnO 2 into a reaction tube and add 5 ml 20% H 2 O 2. Quickly replace the stopper assembly. Page 10 of 18
3. Allow a little gas to pass through the delivery tube (to displace the air) and then collect a test tube of oxygen to directing the tubing underneath one of the water filled test tubes. If the reaction stops add a further 5 ml H 2 O 2. 4. When the test tube is filled with oxygen, stopper it and remove it from the beaker of water. 5. Place a glowing, but not alight, wooden splint into the test tube. The reaction is quite vigorous, with the black MnO 2 foaming quickly. A colourless, odourless gas (O 2 ) is seen filling up the water filled test tubes. Oxygen is collected by downward displacement of water. A glowing splint re-lights when placed inside the test tube. MnO 2 + 2H 2 O 2 (l) O 2 (g) + 2H 2 O(l) Students should be able to explain properties of oxygen gas. Students should be able to explain the role of a catalyst. Students should be able to write a balanced chemical equation for the preparation of oxygen gas. Liquid waste should be washed down the sink with plenty of water. Page 11 of 18
TOPIC: OXIDISING AGENTS AND REACTION RATES Demonstration: Decomposition of hydrogen peroxide Oxidising agents Decomposition reactions Reaction rates and catalysts Safety glasses MUST be worn at all times Wear safety gloves when handling 30% hydrogen peroxide Requirement: 100 ml of 30% hydrogen peroxide, pea-size amount of potassium permanganate, 5 L conical flask, spatula, overhead projector No prior preparation required. Add enough hydrogen peroxide to cover the bottom of the conical flask (about 30ml into 5 L flask). Place the flask on top of a projector and turn on the light. Then quickly add a pea-sized amount of KMnO 4 to the flask. Make sure you are wearing safety glasses When the peroxide is poured into the flask, it looks like it is boiling as i t slowly starts to decompose to a colourless gas. When potassium permanganate is added, suddenly all of the hydrogen peroxide is decomposed and due to lots of heat being given off steam is formed. At the end of the decomposition process, potassium permanganate is seen at the bottom of the flask KMnO 4 2H 2 O 2 (l) ------------------------ 2H 2 O(l) + O 2 (g) Students should appreciate the role of a catalyst in increasing the rate of reaction and not taking part in the reaction. Students should be able to understand decomposition reactions. Students should be able to write a balanced chemical equation for decomposition of hydrogen peroxide. Rinse out the flask with water and wash it down the laboratory sink with plenty of water. Page 12 of 18
TOPIC: CHANGE OF STATE Demonstration: Sublimation of iodine Change of state from solid to gas States of matter Closed system dynamic equilibrium Safety glasses MUST be worn at all times Wear safety gloves when handling iodine Minimise exposure to iodine fumes Requirements: 2 L measuring cylinder, watchglass, iodine crystals No prior preparation required. 1. Place some crystals into the cylinder so that they cover the base. 2. Quickly place the watch-glass on top of the cylinder to enclose the gas. While the reaction starts immediately it will take some time to see the purple gas inside the cylinder, it will take up to about 30 min to see considerable amount of iodine gas. Initially a pale purple gas will be seen in the cylinder. This is most obvious in a well-lit room with a white background. 2I(s) I 2 (g) Students should be able to observe that this is an enclosed system where dynamic equilibrium has been set up between solid and gas states. Students should be able to understand that at atmospheric pressure iodine will directly change state from solid to gas. Students should be able to write a balanced equation for this process. Students should be able to recognise that this is a physical change. Place left over solid iodine back into iodine bottle. TOPIC: REACTIONS OF ACIDS AND BASES Demonstration: Neutralisation reaction Chemical properties of acids and bases ph indicators Acid-base reactions producing carbon dioxide gas Safety glasses must be worn at all times Handle all chemicals with care Requirements: 1 L measuring cylinder Page 13 of 18
100 ml water 2 large spoonfuls of laundry detergent 4 large spoonfuls of NaHCO 3 400 ml beaker 200 ml vinegar 3 ml bromophenol blue indicator A large tray to catch any spills In the 1 L measuring cylinder add the water, detergent and NaHCO 3 and in the beaker mix the vinegar with the indicator. Quickly pour the contents of the beaker into the cylinder. A thick foam is produced, When the vinegar is added the solution in the cylinder changes colour to blue/purple. NaHCO 3 (s) + CH 3 COOH(aq) CH 3 COONa(aq) + H 2 O(l) + CO 2 (g) Students should be able to predict the gas that is evolved when acid reacts with bicarbonate. Students should be able to explain the reason for the colour change. Students should be able to write a balanced chemical equation for this reaction. Dispose of all waste down a laboratory sink with plenty of water. TOPIC: REDOX REACTIONS Demonstration: Zinc and copper sulfate redox reaction Spontaneous redox reactions Oxidation and reduction processes Balancing redox reactions Safety glasses MUST be worn at all times Handle all chemicals with care Equipment: 2 square zinc strips 2 x 200 ml beakers 150 ml of 0.1 mol L-1 CuSO 4 150 ml of 0.1 mol L-1 ZnSO 4 tongs Cut out square zinc strips. 1. Place a zinc strip into each beaker. 2. Pour in CuSO 4 solution into one beaker and ZnSO 4 solution into the other beaker. Page 14 of 18
The Zn metal will react with the copper solution immediately and a brown precipitate will form on the top of the zinc metal, with time the blue solution of the copper sulphate will change to colourless. Nothing happens to the second beaker where zinc is sitting in zinc sulphate solution. After 30 minutes more brown precipitate deposits on the zinc in the copper sulphate solution and still no reaction in the second beaker. Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) E = + 1.1V Zn(s) + ZnSO 4 (aq) No reaction Students should understand and be able to explain the reaction between Zn metal and CuSO 4. Students should understand and be able to explain why there is no reaction between Zn metal and ZnSO 4. Students should be able to write full equations for the redox reactions. Students should be able to predict if a reaction is spontaneous or not. Students should be able to calculate potential of redox reaction. Dispose of liquid waste into a laboratory sink with plenty of water. Dispose of solid waste into a laboratory bin. TOPIC: CHEMICAL PROPERTIES OF ALCOHOLS Demonstration: Oxidation of Alcohol using Dichromate Oxidation of alcohols Wash hands immediately if they come into contact with dichromate Keep flames away from alcohol Equipment: overhead projector 2 crystallization dishes 3 ml spirits 6 ml acidified 0.1molL -1 K 2 Cr 2 O 7 Page 15 of 18
1. Place both crystallization dishes on the overhead projector. 2. Pour half of the K 2 Cr 2 O 7 into each dish. 3. To one dish add 3 ml of the vodka and into the other dish add 3mL of water. After a couple of minutes the dish with the addition of Vodka changes colour from orange to green. Chemical equations: 3CH 3 CH 2 OH + 16H + 2- + 2Cr 2 O 7 3CH 3 COOH + 4Cr 3+ + 11H 2 O (orange) (green) Students should be able to calculate oxidation numbers for an organic reaction. Students should be able to understand the reaction of ethanol with dichromate. Students should be able to write a balanced chemical equation to represent this reaction. Students should be able to predicting the organic product when any alcohol is oxidized. Students should be able to explain how breathalysers work Dispose of dichromate solution into a special waste beaker and follow school s protocols for disposal of this chemical. Wash all other chemicals down laboratory sink with plenty of water. TOPIC: REDUCING SUGARS Demonstration: Silver mirror test Reducing sugars Reactions of monosaccharides, disaccharides and polysaccharides Reactions of aldehydes DO NOT breathe in concentrated ammonia fumes Requirements: 150 ml of 0.1 M AgNO 3 2-4 ml of conc. ammonia solution 4g of glucose 250 ml round bottom flask stopper and pipette No prior preparation. Place 150mL of 0.1M AgNO 3 into 250mL round bottom flask, add 2-4mL of conc. ammonia solution and then add 4g of glucose. Stopper the round bottom flask and swirl solution for about 30min. You can speed up the formation of the mirror by placing the flaks in a hot water bath (700C). As the solution is swirled around the flask the inside of the flask is covered with a reflective material, which looks like mirror. Students should be able to explain what a reducing sugar is. Page 16 of 18
Place any left over silver nitrate into a special silver collection bottle for correct disposal. TOPIC: AMINO ACIDS Demonstration: Iodine fuming fingerprinting Amino acids DO NOT breathe in the fumes of iodine. Requirement: Iodine crystals 1 L beaker or chromatography development tank clean A4 sheet of paper vaseline Place some solid iodine at the bottom of a chromatography developing plastic tank (cylinder like) and cover, allow the iodine fumes to develop. Get a clean sheet of white paper, ask student to place his/her palm on the sheet of paper and then place paper inside the developing tank (sweaty palm gives best results), finger and palm print develops in few minutes. After a few minutes the imprint of the hand appears as a dark brown stain on the paper. Iodine fuming is based on electron-donoracceptor complexes, basically the complex is formed between iodine and the amino acids found in the sweat. Students should be able to understand that sweat contains amino acids. Place any left over iodine back into the iodine bottle. Page 17 of 18