WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE Edexcel Science revision. 00:00:04.125 --> 00:00:07.457 Unit S C 11: Obtaining and using metals. 00:00:10.133 --> 00:00:15.018 The reactivity series orders metals by their tendency to form positive ions. 00:00:15.168 --> 00:00:18.428 A more reactive metal more readily loses electrons. 00:00:21.100 --> 00:00:29.505 The required order is potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. 00:00:29.655 --> 00:00:33.871 Carbon and hydrogen are non-metal comparison points, not metals. 00:00:34.021 --> 00:00:38.703 Carbon guides extraction; hydrogen guides reactions with dilute acid. 00:00:38.853 --> 00:00:40.411 Neither is a metal. 00:00:45.067 --> 00:00:50.328 Potassium, sodium and calcium react with cold water to make hydroxides and hydrogen. 00:00:50.478 --> 00:00:57.634 Magnesium reacts very slowly with cold water but more vigorously with steam; observations depend on conditions. 00:01:00.300 --> 00:01:11.445 Metals above hydrogen generally react with suitable dilute acids to form a salt and hydrogen; copper, silver and gold do not produce hydrogen with dilute hydrochloric acid. 00:01:14.100 --> 00:01:22.600 Compare water, acid and salt-solution reactions using controlled conditions and observations such as gas production or displacement. 00:01:22.750 --> 00:01:26.152 Protective oxide layers can affect apparent reaction rate. 00:01:28.833 --> 00:01:35.115 Aluminium's oxide coating can prevent an immediate reaction despite its high position in the series. 00:01:35.265 --> 00:01:38.833 Distinguish underlying reactivity from a surface barrier. 00:01:41.500 --> 00:01:46.012 A more reactive metal displaces a less reactive metal from its compound. 00:01:46.162 --> 00:01:51.516 A less reactive metal cannot usually displace a more reactive one under the same conditions. 00:01:54.167 --> 00:02:02.027 Zinc plus copper sulfate gives zinc sulfate and copper: Z N plus C U S O 4 produces Z N S O 4 plus C U. 00:02:02.177 --> 00:02:08.104 A copper deposit forms and the blue solution loses colour as C U, charge 2 plus, is removed. 00:02:10.767 --> 00:02:17.300 The ionic equation is Z N plus C U, charge 2 plus, produces Z N, charge 2 plus, plus C U. 00:02:17.450 --> 00:02:22.824 Zinc loses electrons and is oxidised; copper ions gain electrons and are reduced. 00:02:25.500 --> 00:02:34.253 Half-equations are Z N produces Z N, charge 2 plus, plus 2 electrons and C U, charge 2 plus, plus 2 electrons produces C U. 00:02:34.403 --> 00:02:38.841 Both processes occur together, so displacement is a redox reaction. 00:02:38.991 --> 00:02:42.274 Electrons lost by zinc are gained by copper ions. 00:02:46.933 --> 00:02:53.695 Aluminium can reduce copper oxide: 2 A L plus 3 C U O produces A L 2 O 3 plus 3 C U. 00:02:53.845 --> 00:02:59.488 Such competition reactions can be very energetic and require a controlled demonstration. 00:03:02.167 --> 00:03:06.818 Oxidation can also mean gain of oxygen and reduction loss of oxygen. 00:03:06.968 --> 00:03:13.005 Metal extraction from oxides is reduction; use electron transfer for reactions without oxygen. 00:03:15.667 --> 00:03:21.905 An ore is a rock containing enough metal or metal compound to make extraction worthwhile financially. 00:03:22.055 --> 00:03:27.677 Whether it is worth extracting depends on the concentration, extraction costs and metal price. 00:03:30.333 --> 00:03:33.391 Most metals occur as compounds in Earth's crust. 00:03:33.541 --> 00:03:38.203 Very unreactive metals such as gold can occur as uncombined elements. 00:03:40.867 --> 00:03:48.876 For metals below carbon in the series, heating their oxides with carbon or carbon monoxide can remove oxygen and release the metal. 00:03:49.026 --> 00:03:50.882 This route includes iron. 00:03:53.533 --> 00:04:01.735 For iron oxide, a useful reduction equation is F E 2 O 3 plus 3 C O produces 2 F E plus 3 C O 2. 00:04:01.885 --> 00:04:06.004 Iron oxide loses oxygen while carbon monoxide gains it. 00:04:08.667 --> 00:04:16.514 Metals above carbon, including aluminium, cannot be extracted from their oxides by heating with carbon in this GCSE model. 00:04:16.664 --> 00:04:20.139 Electrolysis of a molten ionic compound is needed. 00:04:20.289 --> 00:04:25.419 Use reactivity and costs; electrolysis is of the compound, not molten metal. 00:04:30.100 --> 00:04:39.453 Aluminium extraction uses aluminium oxide dissolved in molten cryolite, lowering the operating temperature compared with melting pure alumina. 00:04:39.603 --> 00:04:42.121 Electrical energy is a major cost. 00:04:44.800 --> 00:04:48.212 Choose a route using reactivity and economic evidence. 00:04:48.362 --> 00:04:55.427 Extraction includes energy, raw material, plant and environmental costs, not just whether a reaction is possible. 00:04:58.100 --> 00:05:02.921 As high-grade ores become less available, lower-grade materials can be considered. 00:05:03.071 --> 00:05:08.755 Biological extraction can recover metals such as copper from low-concentration sources. 00:05:11.433 --> 00:05:16.297 In bioleaching, bacteria help produce soluble metal compounds from ores. 00:05:16.447 --> 00:05:23.196 The resulting leachate contains metal ions that can be recovered, for example by displacement or electrolysis. 00:05:23.346 --> 00:05:26.817 Lower-grade ore can be used, but the process may be slow. 00:05:31.467 --> 00:05:36.299 In phytoextraction, plants take up metal compounds from contaminated soil. 00:05:36.449 --> 00:05:43.211 Harvesting and burning the plants produces ash enriched in metal compounds, from which metal can be extracted. 00:05:45.867 --> 00:05:49.471 Burning plants does not necessarily give pure metal directly. 00:05:49.621 --> 00:05:53.901 A further extraction step is required to recover the metal from the ash. 00:05:54.051 --> 00:05:56.696 The ash is not automatically pure metal. 00:06:01.367 --> 00:06:08.992 These routes may reduce energy demand or mining damage but can be slow and require large areas or careful treatment of solutions. 00:06:09.142 --> 00:06:13.405 Evaluate both advantages and limitations for the particular process. 00:06:16.067 --> 00:06:20.503 Corrosion is reaction of a metal with its surroundings, often oxidation. 00:06:20.653 --> 00:06:28.695 More reactive metals generally have a greater tendency to oxidise, but protective surface coatings can change the observed behaviour. 00:06:31.367 --> 00:06:34.567 Iron rusts when both oxygen and water are present. 00:06:34.717 --> 00:06:40.913 Rust is hydrated iron oxide and is porous, so it does not effectively protect the underlying iron. 00:06:43.567 --> 00:06:47.754 Aluminium forms a thin oxide layer that sticks firmly to its surface. 00:06:47.904 --> 00:06:55.625 This keeps oxygen and water away from the metal underneath, explaining why aluminium resists corrosion despite being fairly reactive. 00:06:58.300 --> 00:07:05.486 Paint, oil or a barrier coating can keep oxygen and water away from iron; protection can fail if the barrier is damaged. 00:07:05.636 --> 00:07:09.841 Galvanising uses zinc, which also offers sacrificial protection. 00:07:12.500 --> 00:07:16.992 Sacrificial protection uses a more reactive metal connected to the iron. 00:07:17.142 --> 00:07:20.581 That metal oxidises instead of the iron, protecting it. 00:07:20.731 --> 00:07:24.132 It is gradually used up and eventually needs replacing. 00:07:26.800 --> 00:07:33.103 Mining and extraction can damage landscapes and habitats, consume energy and produce waste and emissions. 00:07:33.253 --> 00:07:37.931 Recycling can reduce demand for ore and conserve finite metal resources. 00:07:40.600 --> 00:07:47.607 Recycling often uses less energy than extracting a metal from ore, especially aluminium, and can reduce landfill. 00:07:47.757 --> 00:07:52.348 Collection, sorting, transport and remelting still have costs and impacts. 00:07:55.000 --> 00:08:00.438 Separate metals and remove contaminants so the recycled material has suitable properties. 00:08:00.588 --> 00:08:04.171 Mixed alloys can be harder to reuse as a particular pure metal. 00:08:06.833 --> 00:08:14.470 A life-cycle assessment considers obtaining raw materials, manufacturing, use and end-of-life disposal or recycling. 00:08:14.620 --> 00:08:18.457 Include transport and energy where relevant across these stages. 00:08:18.607 --> 00:08:22.455 Consider the same useful service and impacts across all stages. 00:08:27.133 --> 00:08:32.317 Compare products for the same useful service, such as a specified number of drinks served. 00:08:32.467 --> 00:08:38.535 A heavier reusable item may need repeated use to offset its initial manufacturing impact. 00:08:41.200 --> 00:08:48.543 Use quantitative evidence for energy, emissions, waste and resource use; different indicators can favour different options. 00:08:48.693 --> 00:08:53.146 State assumptions and avoid treating a single number as a complete assessment. 00:08:55.800 --> 00:09:04.865 Hypothetical example: a reusable item costs 100 impact units to make and 1 per use; a single-use alternative costs 6 per use. 00:09:05.015 --> 00:09:12.149 At 20 uses they tie at 120; beyond 20, the reusable option is lower in this simplified measure. 00:09:14.800 --> 00:09:17.403 That completes Obtaining and using metals. 00:09:17.553 --> 00:09:20.898 Revisit the notes and test yourself on the revision website.