Metals
Aperçu
At the state banquets of Napoleon III the guests he wished to flatter were handed cutlery made of aluminium, while everybody else had to make do with gold. That is not a joke about French taste. In the 1850s aluminium genuinely was the most expensive metal on the market, and yet it is the commonest metal in the rock beneath your feet. Gold is millions of times rarer. The whole of the puzzle, and the whole of its solution, sits inside this lesson.
What separates the two is not how much of each there is but how tightly each one clings to whatever it has combined with. Gold sits in the ground as gold, waiting to be picked up. Aluminium is locked into its oxide so firmly that nobody could prise it out cheaply until 1886. Order every metal by how strongly it holds on and you get a single list that quietly decides what fizzes in cold water, what merely bubbles in acid, what refuses to do either, how iron is smelted out of an ordinary red rock, and why some metals stay costly however abundant they are.
Objectifs
- Metals can be arranged in an order of their reactivity from their reactions with water and dilute acids. Students should be able to recall and describe the reactions, if any, of potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper with water or dilute acids. Students should be able, where appropriate, to place these metals in order of reactivity.
- Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.
- Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon: for example, iron oxide is reduced in the blast furnace to make iron. Knowledge and understanding are limited to the reduction of oxides using carbon. Knowledge of reduction is limited to the removal of oxygen. Details of the blast furnace are not required, but students should know the raw materials used and explain the simple chemistry involved, including the use of equations. Knowledge of the details of the extraction of other metals is not required. Examination questions may provide further information about specific processes for students to interpret or evaluate.
- Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive. Knowledge of the details of industrial methods of electrolysis is not required, other than the detail required for aluminium (see Section 3.3.2).
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Note de cours
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Évaluation de la leçon
Félicitations, vous avez terminé la leçon sur Metals. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à lépreuve. Cette section propose une variété de pratiques des questions conçues pour renforcer votre compréhension et vous aider à évaluer votre compréhension de la matière.
Vous rencontrerez un mélange de types de questions, y compris des questions à choix multiple, des questions à réponse courte et des questions de rédaction. Chaque question est soigneusement conçue pour évaluer différents aspects de vos connaissances et de vos compétences en pensée critique.
Utilisez cette section d'évaluation comme une occasion de renforcer votre compréhension du sujet et d'identifier les domaines où vous pourriez avoir besoin d'étudier davantage. Ne soyez pas découragé par les défis que vous rencontrez ; considérez-les plutôt comme des opportunités de croissance et d'amélioration.
- Which metal can be extracted from its oxide by heating with carbon? A. potassium B. sodium C. iron D. aluminium Answer: C
- Which of these metals produces no bubbles when it is added to dilute hydrochloric acid? A. magnesium B. zinc C. iron D. copper Answer: D
- Gold is found in the Earth as the metal itself. This is because gold: A. is very dense B. is very unreactive C. has a high melting point D. is a good conductor of electricity Answer: B
- In the blast furnace, iron(III) oxide is reduced to iron. In this topic, reduction means: A. gain of oxygen B. loss of oxygen C. gain of heat D. loss of heat Answer: B
- Aluminium is extracted by electrolysis of a molten compound rather than by heating its oxide with carbon. This is because aluminium is: A. more reactive than carbon B. less reactive than carbon C. of low density D. found in the Earth as the metal itself Answer: A
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