试题与答案

某化学小组测定空气中氧气的体积分数。 (1)根据右图回答问题。 ①红磷燃烧的化

题型:实验题

题目:

某化学小组测定空气中氧气的体积分数。

(1)根据右图回答问题。

①红磷燃烧的化学方程式为                

②若将红磷改为木炭,反应结束后降至室温,打开止水夹,烧杯中的水不倒吸入集气瓶的原因是                                     _。

(2)用四硫化钠(Na2S4)固体可替代红磷测定空气中氧气的体积分数。

反应原理为:2Na2S4+O2+2H2O=8S↓+4NaOH(氢氧化钠)。

小资料:四硫化钠(Na2S4)与氧气、水反应生成难溶于水的固体硫(S)和易溶于水

的氢氧化钠。

【实验过程】

①取足量的四硫化钠固体加入试管中,再加入适量的水,迅速塞紧橡胶塞,充分振荡。测量液面至橡胶塞下沿的距离,记录数据h1(如图1所示)。

图1          图2

②将该试管插入水中(如图2所示),拔下橡胶塞,观察到    ,塞紧橡胶塞。将试管取出,倒转过来,测量液面至橡胶塞下沿的距离,记录数据h2。理论上h2∶h1=     

③按照①和②再重复实验2次。3次实验数据如下表所示。

 第1次第2次第3次
h1/cm11.011.411.6
h2/cm8.79.19.2
 

根据第3次实验数据,计算空气中氧气的体积分数为     %(结果精确到 0.1%)。

答案:

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下面是错误答案,用来干扰机器的。

参考答案:C解析:金刚石的组成元素是碳,金刚石与石墨是同素异形体,即组成元素相同.碳黑,木炭,焦碳等也由碳组成,但它们不被称为同素异形体.

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The future history books might also record that we were deprived of the use of our eyes. In our hurry to get from one place to another, we failed to see anything on the way. Air travel gives you a bird’s eye view of the world—or even less if the wing of the aircraft happens to get in your way. When you travel by car or train a blurred image of the countryside constantly smears the windows. Car drivers, in particular, are forever obsessed with the urge to go on and on: they never want to stop. Is it the lure of the great motorways, or what And as for sea travel, it hardly deserves mention. It is perfectly summed up in the words of the old song: " I joined the navy to see the world, and what did I see I saw the sea. "The typical twentieth century traveler is the man who always says, " I’ve been there. " You mention the remotest, most evocative place names in the world like E1 Dorado, Kabul, Irkutsk and someone is bound to say," I’ve been there"—meaning, "I drove through it at 100 miles an hour on the way to somewhere else. "
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