Exploring Metallic Properties: Reactivity, Rusting & Alloys

At the end of this unit you should: 1. Be able to describe the properties of metals and non-metals. 2. Be able to explain the differences between metals, non-metals and metalloids. 3. Be able to investigate and classify the reactivity series of a selection of metals. 4. Be able to investigate the conditions needed for rusting and to prevent rusting. 5. Be able to describe alloys and their uses.

alloys brittle conductivity corrosion ductile flame test lustre malleable metalloids metals non-metals reactivity series rust sonorous

LIGHTBULB QUESTION Colour-coding in the periodic table tells us which elements are metals, non-metals or metalloids but doesn't tell us why. The way we tell the difference between metals and other substances is by looking at its properties.

KNOWING A METAL • Knowing a metal • Lustre – the shininess of a substance • Hardness • Heat conduction • Electrical conduction • Malleable – can be beaten into shape • Ductile – can be stretched into a thin wire without snapping • Brittle – break, snap or tear easily • Sonorous – can make a clear ringing sound when hit

LIGHTBULB QUESTION The metal of the chair is a good conductor of heat. This means that heat will transfer from the surface of your skin to the metal legs. Also our skin can detect that something is colder or hotter than our body but not the exact number of degrees. Plastic is a poor conductor of heat so heat does not transfer from our skin to it as easily, so it ‘feels’ warmer to touch.

DEMONSTRATION Demonstration 08.02.01 – Elemental flames Equipment: Five grams of lithium chloride, 5 g of sodium chloride, 5 g of potassium chloride, 5 g of barium chloride, 5 g of strontium chloride, 5 g of copper (II) chloride (toxic–handle with care), six spray bottles, distilled/deionised water, Bunsen burner, heat-resistant mats, 1 500 cm3 of industrial methylated spirits (IMS) or ethyl alcohol (ethanol), weigh boats, spatula, top-pan balance.

DEMONSTRATION Instructions: 1. Transfer 250 ml of alcohol to a clean, dry spray bottle, and add 5 g of sodium chloride. 2. Screw the pump assembly tightly onto the neck of the bottle. Make sure the nozzle is closed. Shake until the salt has been dissolved. 3. Remove the pump assembly and add 250 ml of distilled/deionised water and shake until thoroughly mixed. 4. Repeat this procedure for each metal salt. If the metal salt is not a fine powder, it may be necessary to use a mortar and pestle to grind the salt. 5. The Bunsen burner should be set up on heat-resistant mats. Light the Bunsen and turn to blue flame (open collar fully).

DEMONSTRATION Instructions: 6. Allow to burn for several minutes to ensure a steady flow of gas and a well-burning flame. 7. Hold the spray bottle a minimum of 30 cm from the top of the Bunsen flame. 8. Spray for effect. The spray bottle may have to be pumped several times to get a sufficiently powerful and fine mist. Aim for the top of the flame as to do otherwise may extinguish it.

1. Why are alcohol solutions used? • Alcohol burns at a low temperature so an alcohol–water solution burns well without any alcohol colour affecting the colour display.

2. Is the distance between the spray bottle and the Bunsen flame important? How would you prove this? • By varying the distance between the Bunsen burner and the spray bottle. Holding it too close could cause a ‘burn-back’ effect along the spray into the bottle.

3. Flame tests are no longer used to identify elements. Based on this demonstration, can you think of two reasons why this is so? • 1. Flame tests rely on the human eye, which is not good enough to distinguish between all shades of colour consistently. • 2. If only using one Bunsen burner, residue from the alcohol mixtures can build up on the chimney of the Bunsen and cross-contaminate other flame tests, giving false or mixed flame colours.

DEMONSTRATION Demonstration 08.02.02: Testing Group 1 elements Equipment: Water trough, scalpel, clock glass, forceps, three wooden splints, cigarette lighter, safety screen, samples of lithium, sodium and potassium.

DEMONSTRATION Instructions: 1. Half-fill a water trough with tap water, and place behind a safety screen. Students should be 1.5 m from the screen, and the room should be well-ventilated. 2. Using a forceps, remove a cylindrical pellet of lithium from its container, pointing out to students that it is stored under oil. 3. Place the pellet onto a clock glass and, using the scalpel, cut a sliver no thicker than approximately 3 mm from the pellet. Students will hopefully see the colour of the freshly cut metal dull as it oxidises (a visualiser is advantageous here). The forceps may be needed to prevent the pellet from sliding off the clock glass due to the oil. 4. Return the pellet to the lithium container and secure the lid before proceeding further. 5. Light a splint.

DEMONSTRATION Instructions: 6. Drop the sample into the water down the inside of the water trough. 7. As the reaction becomes more vigorous, the sample should move across the trough. The liberated hydrogen gas can be lit with the lighted splint. The reaction will fizzle out or may finish with a very small ‘pop’ sound. 8. Using clean tissue, clean any residue from the clock glass, forceps and scalpel. 9. Repeat these steps with sodium and potassium. 10. If the sample is big enough, the sodium may self-ignite as the oxidation reaction will be enough to ignite the liberated hydrogen gas. The reaction should finish in a small ‘pop’ sound. Potassium has a vigorous reaction so tends to self-ignite regardless of sample size. Caution is needed as the reaction nearly always ends in a popping sound. If the sample is big enough, this can eject debris.

1. What conclusion can you make about all the Group 1 elements? Give reasons for you answer. • There are several possible conclusions: • • All are very reactive with water – fizzing on contact. • • All produce a flammable gas (hydrogen) when reacting with water – can be lit or self-ignite. • • All have low density – float on surface of water/easily cut with a knife.

2. What other properties of Group 1 elements did you notice? Are they similar to other metals? Explain your answer. • In addition to any properties already mentioned: • • Form an oxide quickly when exposed to air – cut surface discolours quickly. • • All have a grey or silver grey colour. • • This is different to other metals, as iron and copper, for example, do not react so quickly or strongly to water or air.

3. Can you explain why these elements are stored under oil? • They are stored under oil because they are so reactive and can oxidise quickly when exposed to air.

Equipment: Two crocodile clips, three wires, bulb (or LED), 6V cell, three salt solutions from previous Demonstration 08.02.01, a selection of other metallic and non-metallic substances/objects, three petri dishes. Investigation 08.02.01: Testing the electrical conductivity of metals and non-metals

Instructions: 1. Set up the test circuit as shown. 2. When testing solids, they can be placed across the crocodile clips directly. 3. When testing liquids (solutions), then a separate petri dish should be used for each solution, to prevent cross-contamination. Investigation 08.02.01: Testing the electrical conductivity of metals and non-metals

1. What other evidence can you use to back up your decisions about whether each material is a metal, non-metal or metalloid? • A heat conductivity test of the same materials.

2. Did any of the test materials that you know to be metals not conduct electricity? Can you explain why? • The metals were possible salts so needed to be dissolved/melted first.

3. This investigation uses electrical conductivity to classify the test materials. If you were given rods of copper, steel, glass and carbon, how would you use heat conductivity to classify each of these materials? How would you make sure it was a fair test? • An equal amount of wax would be added to one end of each rod, the other end of the rod would be heated and the time it took for the wax to melt timed. To ensure a fair test, the rods should be the same length and diameter.

4. Was this electrical conduction investigation a fair test? Justify your answer. • No, because some materials were dissolved in solution and some were not.

Alloy: A mixture of two or more metals.

(a) The members of a church wish to buy a new bell for their bell tower. When positioned, the bell will sit partly exposed to the elements. The committee in charge of buying the bell have been given the choice of three metals: cast iron, steel or bronze. Which metal would you recommend they choose and why? Bronze as it is hard-wearing, and does not corrode easily, and would make a good sound. Both cast iron and steel would make a good sound, but both rust and cast iron can crack with repeated hammering.

(b) Find pictures of objects which are made of each of these three alloys (cast iron, steel and bronze), and not already given in Table 08.02.02.

Corrosion: The undesired process of a metal combining with oxygen to form its oxide. Rusting: The process of iron combining with oxygen to form iron oxide.

Inspect metals in your surroundings (at home or in school) for corrosion. Note if the metals have corrosion and the exact environment they are in. Are there any patterns to the corrosion? Metals will be corroded it they are in constant contact with moisture and air and have no protective coating or the protective coating has been scratched or removed.

(b) Can you suggest why bridges on motorways are made mostly from concrete rather than steel? Give more than one reason for your answer. Concrete is a long-lasting, strong material that does not corrode.

(c) Name the element that is used to protect other metals in the galvanising process. Zinc.

(d) Each of the photographs in Table 08.02.03 show metal that has been protected. How was each object protected? Rewrite Table 08.02.04 into your copy and fill it in.

(e) Garden Furniture Ltd. have asked you to advise them on the best ways to prevent their steel garden gates from rusting. What would you suggest? The gates should be galvanised, which means they can be sold as ‘rust-proof’. Adding paint would increase the protection.

Investigation 08.02.02: Finding out what causes rusting Equipment: Four iron/steel nails, galvanised nail, five test tubes, test tube rack, tap water, boiled water, cooking oil, calcium chloride, cotton wool/rubber stopper, kettle, plastic jug, Pasteur pipette.

Instructions: 1. Place five clean dry test tubes of equal size in the test tube rack. Place an iron nail into four of the test tubes and a galvanised iron nail into the fifth test tube 2. Boil some tap water and allow to cool. 3. Half cover one nail with tap water and completely cover the second nail with tap water. 4. Cover the third nail with an equal amount of the previously boiled water, and add a layer of cooking oil. 5. Add approximately 10–12 small pieces of calcium chloride to the fourth test tube and plug with cotton wool or a rubber stopper. 6. Half cover the galvanised nail with tap water. 7. Leave all the test tubes for 2–3 days and then re-examine.

1. How long is needed to complete your investigation? • Observation over several days will show that oxidation is not a quick process but the amount of rust increases significantly within a few days. • 2. Is there evidence of different amounts of rusting on each nail? Explain. • There should be a clear visual distinction between the volumes of rust on each nail. If not, the nails should be left for an additional twenty-four hours.

3. What is different about the set-up in test tubes A and B? Is there a chemical difference? • Both are exposed to water and oxygen; however, the amount of dissolved oxygen in water is much less than in the air so rusting should occur faster and initially to a greater extent in nail A. • 4. Cotton wool is used in test tube D. What else could be used that might be better than cotton wool? • Cotton wool may allow sufficient air and moisture into the tube to cause some rusting, depending on the amount of calcium chloride used. A stopper would completely seal the tube, thus preventing this.

5. If an iron nail covered in cooking oil or petroleum jelly was used in test tube E, would the result be the same? Why? • The petroleum jelly would give the greatest protection and it is possible no rusting would happen. The cooking oil would only provide partial protection. However, at the pressure points where the nail makes contact with the glass, neither may provide protection.

6. Based on your results, how would you protect iron nails from rusting? Could this method be used with other metals? • Ideally iron metals, steels and other alloys could be kept in sealed containers (rooms) where sufficient drying agent is used. Even if oxygen was available, rusting would not occur.

NEUTRALISATION Reactivity Series: An ordered list of metal reactivities with water, acid and other metals.

Investigation 08.02.03: Reactivity series (Part A) Equipment: Four test tubes, calcium granules, magnesium powder (or sand papered magnesium strip), zinc powder, copper powder (or copper shavings), iron powder, tin powder (or aluminium powder), tap water, dilute hydrochloric acid, 0.4 M copper sulfate solution, retort stand and clamp, Styrofoam cup, thermometer, 400 ml beaker, test tube rack, spatula, graduated cylinder.

Instructions: 1. Place four clean test tubes into a test tube rack. 2. Add an equal amount of tap water to each tube. 3. Using a spatula, add an equal amount of calcium granules, magnesium powder, zinc powder and copper powder to separate test tubes. 4. Record your observations in the table (see below) using a () to indicate a reaction or () to indicate no reaction. Based on the vigour of the reactions, also decide an order of reaction for each metal.

Instructions: 5. Clean the test tubes and add an equal amount of hydrochloric acid to each one. 6. Using a spatula, add an equal amount of calcium granules, magnesium powder, zinc powder and copper powder to separate test tubes. 7. Add the results of this part of the investigation to your results table.

Investigation 08.02.03: Reactivity series (Part B) Equipment: Magnesium powder (or sand papered magnesium strip), zinc powder, copper powder (or copper shavings), iron powder, tin powder (or aluminium powder), tap water, 0.4M copper sulfate solution, retort stand and clamp, Styrofoam cup, thermometer, 400 ml beaker, test tube rack, spatula, graduated cylinder.

Instructions: 1. Place 20 cm3 of copper sulfate solution into a Styrofoam cup and set up as in the diagram. 2. Draw up a results table and record the temperature of the copper sulfate. 3. Use a spatula to add iron powder to the cup. 4. Observe any changes to the reaction mixture and record. 5. After the reaction has finished, clean the Styrofoam cup and refill with 20 cm3 of copper sulfate solution. 6. Repeat the procedure for zinc, tin and magnesium (or alternatives listed above in Part A). 7. Record all your observations as you work through the investigation. 8. Use your observations to decide an order of reactivity.

1. Does the order of reactivities in Part A and Part B match? Why? • No, as not all metals are reactive with water. • 2. Is it scientifically sound to make an overall reactivity series based on two different methods? Why? • If no other methods are available, it is acceptable but with the understanding that it is imperfect and other methods need to be developed.

3. The thermometer in Part B was clamped and the Styrofoam cup was placed into a beaker. This investigation can be done without either of these steps being done. Should it? Why? • It is safer to do it this way as clamping the thermometer and placing the cup inside a beaker prevents toppling of the reaction mixture. • 4. In both Part A and Part B, the tested metals were dissolved into solution. What substance could you use to classify the products of each reaction? • The products of each reaction could be tested for their solubility in water.

Copy and Complete In this unit I learned that metals can conduct electricity and heat but non-metals cannot. In the periodic table most elements are metals. Non-metalshave a lower density than metals so tend to float in water. A mixture of two or more metals to form a substance with different physical propertiesis called an alloy. The undesired process of a metal combining with oxygen is called corrosion. When this process happens with iron it is called rusting. The order in which metals react with water, acid and other metals is known as the reactivity series.

1. Gold and silver have similar melting points at about 1000˚C. This means they can be easily melted by a workshop blowtorch. What other property makes them suitable to be made into jewellery? They are malleable metals which have a high shine and do not tarnish too easily.

Exploring Metallic Properties: Reactivity, Rusting & Alloys