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111 Module 5　A Lesson in a Lab 話題導(dǎo)入 人類從日常生活到宇宙探索都離不開科學(xué)技術(shù)。如果沒有科學(xué)的發(fā)展,我們將仍然處于愚昧無知的原始狀態(tài),科學(xué)技術(shù)是第一生產(chǎn)力,它推動了社會經(jīng)濟、文明的發(fā)展,使我們?nèi)祟惓蔀榱擞钪娴闹魅恕Ｗ鳛橹袑W(xué)生,我們應(yīng)該以“八榮八恥”中的“以崇尚科學(xué)為榮、以愚昧無知為恥”為行為準(zhǔn)則,把智慧和熱情投入到科學(xué)研究和探索中。 背景資料 什么是鐵？ 鐵位于周期表第四周期第Ⅷ族。元素符號為Fe,原子序數(shù)為26,是一種重要的過渡元素。光亮的銀白色金屬,密度7.86g／cm3,熔點1535℃,沸點2750℃。純鐵的抗蝕力相當(dāng)強,但通常的鐵都含有碳和其他元素,因而使它的熔點降低,抗蝕力也減弱。鐵有延展性和導(dǎo)熱性，也能導(dǎo)電。但導(dǎo)電性比銅、鋁都差。鐵能被磁體吸引,在磁場作用下,鐵自身也能產(chǎn)生磁性。 鐵為什么會生銹？ 鐵放的時間長了就會生銹。鐵容易生銹,除了由于它的化學(xué)性質(zhì)活潑以外,同時與外界條件也有很大關(guān)系。水分是使鐵容易生銹的物質(zhì)之一。然而,光有水也不會使鐵生銹,只有當(dāng)空氣中的氧氣溶解在水里時,氧在有水的環(huán)境中與鐵反應(yīng),才會生成一種叫氧化鐵的東西,這就是鐵銹。鐵銹是一種棕紅色的物質(zhì),它不像鐵那么堅硬,很容易脫落,一塊鐵完全生銹后,體積可脹大8倍。如果不除去鐵銹,這海綿狀的鐵銹特別容易吸收水分,鐵也就爛得更快了。 引入型閱讀 Chemical Change and Physical Change There are two kinds of changes—chemical change and physical change. In a chemical change,there is always a new substance formed.Breaking up water into hydrogen and oxygen is a chemical change.In each of the chemical change at least one new substance is formed.A change is not a chemical change if it doesn’t form a new substance. Physical changes are very common,too.There are many examples.You can make a physical change by tearing a piece of paper in two,or by cutting a piece of iron with lathe.Here paper is still paper,and the iron is still iron. Another way of making physical change is dissolving something in water.When you dissolve salt in water,the salt disappears.You may think that a new substance has been formed.But really there is no new substance.The salt is still salt.You can still taste it.So the dissolving of anything is a physical change. When water freezes,the change is also a physical one.The water changes from liquid to solid.But it is still the same substance.That is why the freezing of anything is a physical change. 1.It is not ________if a new substance is not formed in the change. A.a physical change B.a chemical change C.change of state D.a change 2.The dissolving of salt in water is ________. A.a physical change B.a chemical change C.hydrogen and oxygen D.breaking up 3.The change of the three states of water is ________. A.a chemical change B.different substances C.a physical change D.the same state 答案:1.B　2.A　3.C 111