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问题 实验题

(8分)某校化学兴趣小组，通过下列装置探究Na2CO3和NaHCO3的热稳定性，设计如下的探究方案，请你参与并完成该探究方案。

(1)提出假设：Na2CO3或NaHCO3加热分解时可能有CO2生成。

(2)设计实验：①利用右图装置分别对一定量的Na2CO3和NaHCO3进行加热；②为了检验CO2的生成，试管B中应加入的物质是_____________(填“澄清的石灰水”或“NaOH溶液”)

(3)现象与结论：同学们发现只有在加热NaHCO3时，试管B中才有气泡产生且有_______________沉淀生成(填沉

淀的颜色)，说明Na2CO3和NaHCO3的热稳定性是：Na2CO3____    ___ NaHCO3(填“＞”或“＜”)。

(4)某同学在探究NaHCO3的热稳定性时，称取了8.4gNaHCO3，充分加热，请你计算理论上可产生CO2气体的体积为__________L(标准状况)

答案

  (2)澄清的石灰水  (3)白色 ＞   (4)2.24

检验CO2的存在，一般用澄清的石灰水。石灰水和CO2反应生成碳酸钙沉淀。碳酸氢钠受热易分解，因此碳酸钠的稳定性强于碳酸氢钠的。碳酸氢钠分解的方程式为2NaHCO3=Na2CO3＋H2O＋CO2↑，如果温度高，则碳酸钠也有可能分解生成CO2，所以根据碳原子守恒可知，理论上生成的CO2为。

单项选择题

发挥药效最快的给药途径是

A．口服

B．外敷

C．吸入

D．皮下注射

E．静脉注射
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单项选择题

Questions 16～20


It is already common knowledge, on the beaches and in the cafes of mainland Europe, that Americans work too hard—just as it is well known on the other side of the Atlantic that Europeans, above all the French and the Germans, are slackers who could do with a bit of America’s vigorous work ethic.
But a new survey suggests that even those vacations American employees do take are rapidly vanishing, to the extent that 40 per cent of workers questioned at the start of the summer said they had no plans to take any holiday at all for the next six months, more than at any time since the late 1970s.
It is probably mere coincidence that George W. Bush, one of the few Americans who has been known to enjoy a French-style month off during August, cut back his holiday in Texas to a fortnight. But the survey by the Conference Board research group, along with other recent statistics, suggests an epidemic of overwork among ordinary Americans.
A quarter of people employed in the private sector in the US get no paid vacation at all, according to government figures. Unlike almost all other industrialized nations, including Britain, American employers do not have to give paid holidays.
The average American gets a little less than four weeks of paid time off, including public holidays, compared with 6.6 weeks in the UK—where the law requires a minimum of four weeks off for full-time workers—and 7.9weeks for Italy. One study showed that people employed by the US subsidiary of a London-based bank would have to work there for 10 years just to be entitled to the same vacation time as colleagues in Britain who has just started their jobs.
Even when they do take vacations, overworked Americans find it hard to switch off. One in three find not checking their email and voicemail more stressful than working, according to a study by the Travelocity website, while the traumas of travel take their own toll. "We commonly complain we need a vacation from our vacations," the author Po Bronson wrote recently. "We leave home tired; we come back exhausted "
Christian Schneider, a German-born scholar at the Wharton business school in Philadelphia, argues that there is "a tendency to really relax in Europe, to disengage from work. When an American finally does take those few days of vacation per year they are most likely to be in constant contact with the office. "
Mindful that well-rested workers are more productive than burnt-out ones, the accounting firm PricewaterhouseCoopers has started closing all its US offices completely twice a year, for 10 days over Christmas and about five around Independence Day. "We wanted to create an environment where people could walk away and not worry about missing a meeting, a conference call or 300 emails," Barbara Kraft, a partner at the company, told the New York Times.
Left to themselves, Americans fail to take an average of four days of their vacation entitlement—an annual national total of 574 million unclaimed days.

According to the first paragraph, what do the people in America think of Europeans ______

A. They work less vigorously except the French and the Germans.
B. They work almost as vigorously as Americans.
C. They should work with some more vigor as Americans do.
D. They could work a bit more vigorously than Americans.
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