题干

现有一瓶无色、有特殊气味的液体,是甲醇(CH3OH)或乙醇(C2H5OH).通过测定该液体充分燃烧后生成的二氧化碳和水的质量可确定是哪种物质,解释原理.

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反应后生成了二氧化碳和水,则根据质量守恒定律,化学反应前后元素的种类质量不变,则反应物中一定含有C、H元素;已知生成的二氧化碳和水的质量,则根据二氧化碳和水的质量,利用某元素的质量=化合物的质量×该元素的质量分数可求出碳元素和氢元素的质量比;再根据碳元素和氢元素的质量比即可求得碳元素与氢元素的原子个数比;最后与反应前甲醇和乙醇中的碳氢个数比对照,即可知道是哪种物质.

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    Every day, a homeowner in Pennsylvania is reminded of a mistake he made 13 years ago. At around 8 in the evening, his peaceful house comes alive with the noise of an alarm clock he dropped into the wall over ten years ago. It's been stuck in the wall ever since.

    13 years ago, Jerry Lynn wanted to make a hole through his living room wall, so he could pass the television cable (电缆)through it. He didn't want to destroy any pipes in the wall, so he came up with a good idea to make sure that he was drilling(钻孔) in an empty place. He took his alarm clock, tied it to a string(线) and set it to go off in 10 minutes. Then he lowered it into the wall, and waited for it to ring. His goal was to drill a hole in a safe place near the place where the ringing was coming from, making sure that there was nothing to pass through there. It all went smoothly until the alarm clock fell into the wall.

The man didn't get back the alarm clock, but thought it would probably run out of battery(电池)in several months, so he wasn't too worried about it. But 13 years later, the alarm clock still rings every day.

    As you can imagine, Jerry and his wife have gotten used to the ringing living room wall, but it can still surprise  guests. So Jerry decides to pull down that wall, just to stop that boring thing, though after putting up with it for 13 years, he think it will be a pity. He says, “I've never herd of a clock battery lasting that long and my friends think it may be interesting to see how long it will keep ringing for.”