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问题 实验题

某化学小组采用类似制乙酸乙酯的装置(如下图)，以环己醇制备环己烯：

已知：

 密度(g/cm3)熔点(℃)沸点(℃)溶解性
环己醇0.9625161能溶于水
环己烯0.81－10383难溶于水
(1)制备粗品

将12.5 mL环己醇加入试管A中，再加入1 mL浓硫酸，摇      

匀后放入碎瓷片，缓慢加热至反应完全，在试管C内得到环己烯粗品。

①A中碎瓷片的作用是________，导管B除了导气外还具有的作用是________。

②试管C置于冰水浴中的目的是________________________________________。

(2)制备精品

①环己烯粗品中含有环己醇和少量酸性杂质等。先加入Na2CO3溶液，振荡、静置、分层，环己烯在________层(填“上”或“下”)，分液后用水洗涤。

②再将环己烯按下图装置蒸馏，冷却水从________口进入(填“g”或“f”)。蒸馏时要加入生石灰，目的是________________________________________。

③实验制得的环己烯精品质量低于理论产量，可能的原因是________。

A．蒸馏时从70 ℃开始收集产品

B．环己醇实际用量多了

C．制备粗品时环己醇随产品一起蒸出

答案

（1）①防暴沸  冷凝  ② 减少环己烯的挥发

(2) ①上   ②  g 除去产品中所含的水分  （3）C

题目分析：（1）①反应需要加热，则A中碎瓷片的作用防暴沸。由于生成的环己烯的沸点为83℃，要得到液态环己烯，导管B除了导气外还具有冷凝作用，便于环己烯冷凝。

②由于环己烯的熔沸点低，所以C中冰水的作用是减少环己烯的挥发。

（2）①环己烯的密度小于水的，且不溶于水，则在上层。

②在冷凝管中冷却水的流向应该和蒸汽的流向相反，所以应该是g口进入。生石灰极易和水反应，所以蒸馏时要加入生石灰的目的是除去产品中所含的水分。

③实验制得的环己烯精品质量低于理论产量，这说明反应物的转化率低。原因环己醇也是乙挥发的，因此可能的原因是制备粗品时环己醇随产品一起蒸出，答案选C。

点评：本题以有机合成为载体综合考查了实验室制环己烯的知识和醇、烃的性质，考查了同学们组合运用实验的能力，题目难度中等，注意把握实验原理和方法，特别是实验的基本操作，学习中注意积累

填空题

信息安全中， 【16】 是指在应用层对信息的保密性、完整性和来源真实性进行保护和认证。
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单项选择题


Nine states and the District of Columbia are doing away with the sales tax on items such as clothes, shoes and even notebooks over the next few weeks, just in time for back-to- school shopping.
Most of the promotions last only a few days, so shoppers will have to act quickly to get a tax break. The tax holidays, which have already expired in two other states, apply to small and large items. For example, the tax break applies to any school supply that costs $15 or less in New Mexico. In Massachusetts, it covers most retail purchases of $2,500 or less. Stores may offer additional savings because these events "give retailers an opportunity to have a sale on top of what the state is doing," says Verenda Smith, government affairs associate at the Federation of Tax Administrators.
No industry-wide figures are available about how much consumers save annually from these tax breaks. But Texas estimates that shoppers will save $47.4 million in taxes this year, nearly a 3 percent increase from the previous year. Massachusetts says shoppers saved roughly $10 million in taxes during its 2005 event.
States that cast aside these promotions when a slow economy pinched state budgets are now reviving them in hopes of stimulating local economies. Some states also believe the gain in consumer goodwill helps balance out the loss in tax revenue.
In some cases, tax losses are minimal because serious shoppers don’t stop at clothes and books. "While states give up sales tax, they usually break even on sales-tax collection," says J. Craig Shearman, a vice-president at the National Retail Federation.
Sophie Beckmann, a certified public accountant at A. G. Edwards in St. Louis, says she’ll avoid that temptation by making a list of necessities. On the Missouri resident’s shopping list: notebooks, pencils, glue and three or four outfits for her son, who is entering the fifth grade this month. She plans to pocket any tax savings. "When you start buying more and spending more just because of the savings, then you’re not doing yourself a favor," Beckmann says.

The phrase "consumer goodwill" underlined in Paragraph 4 most possibly refers to the ______ .

A．other extreme losses in tax revenue

B．pleasant feeling the consumers may have

C．good consumption the market may sustain

D．confidence consumers have over the goods
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