Module 5 A Lesson in a Lab
module 5 a lesson in a lab
話題導入
人類從日常生活到宇宙探索都離不開科學技術。如果沒有科學的發展,我們將仍然處于愚昧無知的原始狀態,科學技術是第一生產力,它推動了社會經濟、文明的發展,使我們人類成為了宇宙的主人。作為中學生,我們應該以“八榮八恥”中的“以崇尚科學為榮、以愚昧無知為恥”為 行為準則,把智慧和熱情投入到科學研究和探 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。鐵有延展性和導熱性，也能導電。但導電性比銅、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,除了由于它的化學性質活潑以外,同時與外界條件也有很大關系。水分是使 鐵容易生銹的物質之一。然而,光有水也不會使鐵生銹,只有當空氣中的氧氣溶解在水里時,氧在有水的環境中與鐵反應,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,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 le ast one new substance is formed.a change is not a chemica l change if it doesn’t for m 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 somethin g in water.when you dissolve salt in
water,the salt disappears.you may think that a new substance has be en 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 dissol ving 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.differen t substances
c.a physical change
d.the same state
答案:1.b 2.a 3.c