用高岭土（主要成分是Al2O3·2SiO2·2H2O，并含有少量CaO、Fｅ2O3）研制新型净水剂（铝的化合物）。其步骤如下：将土样和纯碱混合均匀，加热熔融，冷却后加盐酸分别得到沉淀和溶液，溶液即为净水剂。
（1）写出熔融时主要成分与纯碱反应的化学方程式（Al2O3与强碱反应相似） 。
（2）最后的沉淀是 ，生成沉淀的离子方程式是 。
（3）实验室中常用的有瓷坩埚、氧化铝坩埚和铁坩埚，本实验应选用 坩埚。
（1）SiO2＋Na2CO3
Na2SiO3＋CO2↑
Al2O3＋Na2CO3
2NaAlO2＋CO2↑
（2）H2SiO3 SiO2-3＋2H＋ H2SiO3↓
（3）铁
搞清高岭土的主要成分是本题的关键。Al2O3与SiO2能分别与Na2CO3反应得到Na2SiO3和NaAlO2，冷却后加盐酸分别得到H2SiO3沉淀和AlCl3溶液（净水剂）。瓷坩埚、氧化铝坩埚都能与Na2CO3反应，因此本实验应该选用铁坩埚。
Section C Directions: Read the following text and choose the most suitable heading from the list A-F for each paragraph. There is one extra heading which you do not need.(本题请涂在答题卡上) (E)
80.______ Although credit cards are already a more acceptable part of the financial dealings, they are still regarded, especially in the time of a serious economic crisis, by many as being a major part of the “live now pay later” system. Along with hire-purchase regulations, credit cards, according to some, provide encouragement to spend more money. However, it’s only the fool who is dominated by the temptation to live, temporarily at least, beyond their means, and such people would no doubt manage to do so even without credit cards. 81.______ Advertising campaigns have already promoted a growing realization of the advantages of these small pieces of plastic. They avoid the need to carry large amounts of cash and are always useful in emergencies. And the monthly credit card bill is a loyal booker keeping your monthly purchase record and indicating your buying habits. 82.______ All the credit card organizations charge interest on a monthly basis which may work out as high as two percent a year. But sensible purchase using a card can mean that you obtain up to seven weeks interest-free credit. Using the card abroad, where items frequently take a long time to be included on your account, can extend this period even further. 83.______ It is worthwhile consulting more credit card companies before deciding on a particular credit card. It is necessary to consider the amount of credit granted, interest rates, which may vary slightly; the number and range of outlets, though most cards cover major stores. 84.______ Undoubtedly, if used wisely, a credit card can cost nothing, or at lease help to tide you over a period of financial difficulty. However, we should also remember that the wrong use of the little plastic may drag us deep into financial troubles. More than half of the American personal bankruptcy(破产) and credit failure cases are connected with the wrong use of the credit card. Therefore, every time you open your wallet and reach for a credit card, remember to ask yourself:” Is the item necessary to me?” and “Do I really need so many credit cards?” |