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问题 实验题

(4分)某化学课堂围绕“酸碱中和反应”，在老师引导下开展探究活动，请你和同学们一起进行实验探究。

【演示实验】将一定量的稀H2SO4加入到盛有NaOH溶液的小烧杯中。

【知识梳理】该反应的化学方程式为（1）　            ；

【提出问题】实验中未观察到明显现象，部分同学产生了疑问：反应后溶液中溶质是什么呢？

【猜想与假设】

甲组：只有Na2SO4    乙组：有Na2SO4和H2SO4 丙组：有Na2SO4和NaOH         

【收集证据】丙组同学取烧杯中的溶液少量于试管中，滴加几滴酚酞试液溶液，无明显变化，溶液中一定没有（2）            。

【表达与交流】为了验证其余猜想，甲组同学的实验方案是取少量试液于试管中，滴加氯化钡溶液，观察是否有白色沉淀产生。你认为他们的实验方案（3）        （填“正确”或“不正确”），你的理由是（4）                。

乙组同学取少量试液于试管中，加入（5）______             溶液，振荡，观察到（6）___________________________，证明自己的猜想是正确的。

【反思与评价】为回收硫酸钠，应取剩余试液于烧杯中，加入（7）______ 溶液，充分搅拌，蒸发即可得到纯净的硫酸钠。

答案

（1）H2SO4+2NaOH=NaSO4+2H2O    （2）NaOH    （3）不正确

（4）硫酸和氢氧化钠反应生成硫酸钠，不管溶液中是否含硫酸，无色溶液中都会出现白色沉淀

（5）碳酸钠（或碳酸钾或碳酸氢钠、活泼金属、石蕊等）

（6）气泡      （7）适量的碳酸钠（或氢氧化钠）

题目分析：（1） 将稀H2SO4加入到盛有NaOH溶液中, 反应的化学方程式为: H2SO4+2NaOH=NaSO4+2H2O

（2）由于无色酚酞遇碱溶液变红，而取烧杯中的溶液少量于试管中，滴加几滴酚酞试液溶液，无明显变化，溶液中一没有NaOH

（3） 甲组同学的实验方案是取少量试液于试管中，滴加氯化钡溶液，观察是否有白色沉淀产生。你认为他们的实验方案不正确

（4）理由是：硫酸和氢氧化钠反应生成硫酸钠，不管溶液中是否含硫酸，无色溶液中都会出现白色沉淀

（5）抓住甲乙组同学猜想的不同点，是乙组同学中含有硫酸，而甲组同学的猜想中不含硫酸，所以应抓住酸的化学性质，乙组同学取少量试液于试管中，加入碳酸钠（或碳酸钾或碳酸氢钠、活泼金属、石蕊等），若产生气泡等

（6）为回收硫酸钠，就是相当要除去硫酸钠中的硫酸，抓住除杂质的原则，不能引入新的杂质，应取剩余试液于烧杯中，加入适量的碳酸钠（或氢氧化钠）溶液，充分搅拌，蒸发即可得到纯净的硫酸钠

单项选择题

特种劳动防护用品实行()制度。

A．安全标志管理 

B．登记 

C．备案 
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单项选择题

New tectmology links the world as never before. Our planet has shrunk. It’s now a "global village" where countries are only seconds away by fax or phone or satellite link. And, of course, our ability to benefit from this high-tech communications equipment is greatly enhanced by foreign language skills.
Deeply involved with this new technology is a breed of modem business people who have a growing respect for the economic value of doing business abroad. In modem markets, success overseas often helps support domestic business efforts.
Overseas assignments are becoming increasingly important to advancement within executive ranks. The executives stationed in another country no longer need fear being "out of sight and out of mind." He or she can be sure that the overseas effort is central to the company’s plan for success, and that promotions often follow or accompany an assignment abroad. If an employee can succeed in a difficult assignment overseas, superiors will have greater confidence in his or her ability to cope back in the United States where cross-cultural considerations and foreign language issues are becoming more and more prevalent.
Thanks to a variety of relatively inexpensive communications devices with business applications, even small businesses in the United States are able to get into international markets.
English is still the international language of business. But there is an ever-growing need for people who can speak another language. A second language isn’t generally required to get a job in business, but having language skills gives a candidate the edge when other qualifications appear to be equal.
The employee posted abroad who speaks the country’s principal language has an opportunity to fast forward certain negotiations, and can have the cultural insight to know when it is better to move more slowly. The employee at the home office who can communicate well with foreign clients over the telephone or by fax machine is an obvious asset to the firm.

The word "move" underlined in Paragraph 6 means to ______ .

A．change position or place

B．take action or do something

C．propose formally for discussion and decision

D．persuade somebody to change his attitude
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