WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE Edexcel Science revision. 00:00:04.125 --> 00:00:07.531 Unit C C 11: Obtaining and using metals. 00:00:10.200 --> 00:00:15.085 The reactivity series orders metals by their tendency to form positive ions. 00:00:15.235 --> 00:00:18.495 A more reactive metal more readily loses electrons. 00:00:21.167 --> 00:00:29.571 The required order is potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. 00:00:29.721 --> 00:00:33.937 Carbon and hydrogen are non-metal comparison points, not metals. 00:00:34.087 --> 00:00:38.770 Carbon guides extraction; hydrogen guides reactions with dilute acid. 00:00:38.920 --> 00:00:40.477 Neither is a metal. 00:00:45.133 --> 00:00:50.395 Potassium, sodium and calcium react with cold water to make hydroxides and hydrogen. 00:00:50.545 --> 00:00:57.701 Magnesium reacts very slowly with cold water but more vigorously with steam; observations depend on conditions. 00:01:00.367 --> 00:01:11.512 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. 00:01:14.167 --> 00:01:22.667 Compare water, acid and salt-solution reactions using controlled conditions and observations such as gas production or displacement. 00:01:22.817 --> 00:01:26.219 Protective oxide layers can affect apparent reaction rate. 00:01:28.900 --> 00:01:35.181 Aluminium's oxide coating can prevent an immediate reaction despite its high position in the series. 00:01:35.331 --> 00:01:38.900 Distinguish underlying reactivity from a surface barrier. 00:01:41.567 --> 00:01:46.079 A more reactive metal displaces a less reactive metal from its compound. 00:01:46.229 --> 00:01:51.583 A less reactive metal cannot usually displace a more reactive one under the same conditions. 00:01:54.233 --> 00:02:02.093 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. 00:02:02.243 --> 00:02:08.171 A copper deposit forms and the blue solution loses colour as C U, charge 2 plus, is removed. 00:02:10.833 --> 00:02:17.367 The ionic equation is Z N plus C U, charge 2 plus, produces Z N, charge 2 plus, plus C U. 00:02:17.517 --> 00:02:22.891 Zinc loses electrons and is oxidised; copper ions gain electrons and are reduced. 00:02:25.567 --> 00:02:34.320 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. 00:02:34.470 --> 00:02:38.908 Both processes occur together, so displacement is a redox reaction. 00:02:39.058 --> 00:02:42.341 Electrons lost by zinc are gained by copper ions. 00:02:47.000 --> 00:02:53.762 Aluminium can reduce copper oxide: 2 A L plus 3 C U O produces A L 2 O 3 plus 3 C U. 00:02:53.912 --> 00:02:59.555 Such competition reactions can be very energetic and require a controlled demonstration. 00:03:02.233 --> 00:03:06.885 Oxidation can also mean gain of oxygen and reduction loss of oxygen. 00:03:07.035 --> 00:03:13.071 Metal extraction from oxides is reduction; use electron transfer for reactions without oxygen. 00:03:15.733 --> 00:03:21.972 An ore is a rock containing enough metal or metal compound to make extraction worthwhile financially. 00:03:22.122 --> 00:03:27.743 Whether it is worth extracting depends on the concentration, extraction costs and metal price. 00:03:30.400 --> 00:03:33.458 Most metals occur as compounds in Earth's crust. 00:03:33.608 --> 00:03:38.269 Very unreactive metals such as gold can occur as uncombined elements. 00:03:40.933 --> 00:03:48.943 For metals below carbon in the series, heating their oxides with carbon or carbon monoxide can remove oxygen and release the metal. 00:03:49.093 --> 00:03:50.949 This route includes iron. 00:03:53.600 --> 00:04:01.801 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. 00:04:01.951 --> 00:04:06.071 Iron oxide loses oxygen while carbon monoxide gains it. 00:04:08.733 --> 00:04:16.581 Metals above carbon, including aluminium, cannot be extracted from their oxides by heating with carbon in this GCSE model. 00:04:16.731 --> 00:04:20.205 Electrolysis of a molten ionic compound is needed. 00:04:20.355 --> 00:04:25.486 Use reactivity and costs; electrolysis is of the compound, not molten metal. 00:04:30.167 --> 00:04:39.520 Aluminium extraction uses aluminium oxide dissolved in molten cryolite, lowering the operating temperature compared with melting pure alumina. 00:04:39.670 --> 00:04:42.187 Electrical energy is a major cost. 00:04:44.867 --> 00:04:48.279 Choose a route using reactivity and economic evidence. 00:04:48.429 --> 00:04:55.494 Extraction includes energy, raw material, plant and environmental costs, not just whether a reaction is possible. 00:04:58.167 --> 00:05:02.987 As high-grade ores become less available, lower-grade materials can be considered. 00:05:03.137 --> 00:05:08.821 Biological extraction can recover metals such as copper from low-concentration sources. 00:05:11.500 --> 00:05:16.363 In bioleaching, bacteria help produce soluble metal compounds from ores. 00:05:16.513 --> 00:05:23.263 The resulting leachate contains metal ions that can be recovered, for example by displacement or electrolysis. 00:05:23.413 --> 00:05:26.883 Lower-grade ore can be used, but the process may be slow. 00:05:31.533 --> 00:05:36.365 In phytoextraction, plants take up metal compounds from contaminated soil. 00:05:36.515 --> 00:05:43.277 Harvesting and burning the plants produces ash enriched in metal compounds, from which metal can be extracted. 00:05:45.933 --> 00:05:49.537 Burning plants does not necessarily give pure metal directly. 00:05:49.687 --> 00:05:53.967 A further extraction step is required to recover the metal from the ash. 00:05:54.117 --> 00:05:56.763 The ash is not automatically pure metal. 00:06:01.433 --> 00:06:09.059 These routes may reduce energy demand or mining damage but can be slow and require large areas or careful treatment of solutions. 00:06:09.209 --> 00:06:13.471 Evaluate both advantages and limitations for the particular process. 00:06:16.133 --> 00:06:20.570 Corrosion is reaction of a metal with its surroundings, often oxidation. 00:06:20.720 --> 00:06:28.762 More reactive metals generally have a greater tendency to oxidise, but protective surface coatings can change the observed behaviour. 00:06:31.433 --> 00:06:34.633 Iron rusts when both oxygen and water are present. 00:06:34.783 --> 00:06:40.979 Rust is hydrated iron oxide and is porous, so it does not effectively protect the underlying iron. 00:06:43.633 --> 00:06:47.821 Aluminium forms a thin oxide layer that sticks firmly to its surface. 00:06:47.971 --> 00:06:55.691 This keeps oxygen and water away from the metal underneath, explaining why aluminium resists corrosion despite being fairly reactive. 00:06:58.367 --> 00:07:05.553 Paint, oil or a barrier coating can keep oxygen and water away from iron; protection can fail if the barrier is damaged. 00:07:05.703 --> 00:07:09.907 Galvanising uses zinc, which also offers sacrificial protection. 00:07:12.567 --> 00:07:17.059 Sacrificial protection uses a more reactive metal connected to the iron. 00:07:17.209 --> 00:07:20.648 That metal oxidises instead of the iron, protecting it. 00:07:20.798 --> 00:07:24.199 It is gradually used up and eventually needs replacing. 00:07:26.867 --> 00:07:33.169 Mining and extraction can damage landscapes and habitats, consume energy and produce waste and emissions. 00:07:33.319 --> 00:07:37.997 Recycling can reduce demand for ore and conserve finite metal resources. 00:07:40.667 --> 00:07:47.673 Recycling often uses less energy than extracting a metal from ore, especially aluminium, and can reduce landfill. 00:07:47.823 --> 00:07:52.415 Collection, sorting, transport and remelting still have costs and impacts. 00:07:55.067 --> 00:08:00.505 Separate metals and remove contaminants so the recycled material has suitable properties. 00:08:00.655 --> 00:08:04.237 Mixed alloys can be harder to reuse as a particular pure metal. 00:08:06.900 --> 00:08:14.537 A life-cycle assessment considers obtaining raw materials, manufacturing, use and end-of-life disposal or recycling. 00:08:14.687 --> 00:08:18.524 Include transport and energy where relevant across these stages. 00:08:18.674 --> 00:08:22.521 Consider the same useful service and impacts across all stages. 00:08:27.200 --> 00:08:32.383 Compare products for the same useful service, such as a specified number of drinks served. 00:08:32.533 --> 00:08:38.601 A heavier reusable item may need repeated use to offset its initial manufacturing impact. 00:08:41.267 --> 00:08:48.609 Use quantitative evidence for energy, emissions, waste and resource use; different indicators can favour different options. 00:08:48.759 --> 00:08:53.213 State assumptions and avoid treating a single number as a complete assessment. 00:08:55.867 --> 00:09:04.931 Hypothetical example: a reusable item costs 100 impact units to make and 1 per use; a single-use alternative costs 6 per use. 00:09:05.081 --> 00:09:12.216 At 20 uses they tie at 120; beyond 20, the reusable option is lower in this simplified measure. 00:09:14.867 --> 00:09:17.469 That completes Obtaining and using metals. 00:09:17.619 --> 00:09:20.965 Revisit the notes and test yourself on the revision website.