mandy asked in 科學及數學化學 · 1 decade ago

F.4 Chem 2

1 a) Explain the following:

a) Steel hot water tanks often have a bar of magnesium suspended in the water.

b) A battered tin car rust more quickly than a damged galvanized iron rubbish bin.

2.Explain the following statements:

a ) The Copper and Bronze Ages occurred before the Iron Age.

b) It is more important to recycle aluminium drink cans than steel food cans.

c) Aluminium is more expensive than iron even through it is more abundant.

Update:

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1 Answer

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  • 莫愁
    Lv 6
    1 decade ago
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    Steel hot water tanks often have a bar of magnesium suspended in the water.

    Ans:

    As you know, temperature is one of the important factors affecting chemical reaction(i.e. in this reaction, oxidation) to carry out. Hot water provides higher temperature so that the rate of chemical reaction, rusting, must occur at rapid rate. To prevent rusting from occurring, Mg is used. Mg provides e- to steel so that it doesn't rust.Sacrificial protection.

    Mg-------> Mg2+ + 2e- instead of rusting of steel.

    A battered tin car rust more quickly than a damged galvanized iron rubbish bin.

    For the electrochemical series, Fe is more reactive(i.e. has a more -ve standard electro-potential) than Tin. Hence once Fe is exposed into air and moisture, rusting occurs in Fe rather than Tin. This means that Fe becomes anode (oxidation at anode) instead of tin to react with the O2 and moisture coming from air.

    Please pay more attention to the chemistry about rusting:

    Ans:

    1st step:[andoe] Fe------------->Fe2+ + 2e- oxidation of iron (oxidation at anode)

    2nd step:[cathode] O2 +2H20 + (4e-) ------------------>4OH- formation of hydroxide (reduction at cathode)

    3rd step: Fe2+ + (2OH-) ---------------> Fe(OH)2 formation of iron(II) hydroxide

    4th step: further oxidation of iron(II) hydroxide 4Fe + 3O2 + 6H2O -----> 4Fe(OH)3

    5th step: 4Fe(OH)3 lose water becoming rust Fe2O3*xH20

    remark: [*means hydrated as CuSO4*5H2O]

    2.Explain the following statements:

    a ) The Copper and Bronze Ages occurred before the Iron Age.

    Ans:

    Those metals are naturally-occurring在大自然出現的 and without to be extracted by using very high temperature at about 2500 degree centigrade(2500度) . Be aware that in those years, science was not as well-developed as today. Hence high temperature environment can't be created easily.

    Besides, for those more reactive metals such as Na,K and Ca are created by electrolysis. In those day, not battery was invented. Battery was inverted in 18century.This explain why more reactive metal can't be found easily.

    b) It is more important to recycle aluminium drink cans than steel food cans.

    Ans:

    Since metals are non-renewable sources. Once they are completely used, we will short of them. Hence conservation and recycling is thus important to all of us.

    c) Aluminium is more expensive than iron even through it is more abundant.

    Ans:

    Since it requires more steps such as heating and electrolysis during extraction Al when it is in oxide form comparing Fe which can be reduced by using CO or Carbon at high temperature >600 degree centigrade in school lab. . As more energy is used in reducing its(Al) oxide, price will be higher. I should remind you that Al is more reactive than Fe. Hence once it is in oxide form, higher temperature and more steps such as the use of electrolysis are employed.所謂羊毛出在羊身上, 這些步驟錢(reduction of Al)會轉給用家.

    As a result Aluminium is more expensive than iron even through it is more abundant

    e- = electrons

    -ve = negative

    I hope my information can help you. And sorry for too late to answer your question(我聽日要交!!!!!!!!!!!!!THX .) Agan Sorry!!!

    2007-01-29 16:00:52 補充:

    對不起,不知何出不到箭咀-------------> = -----------------

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