题目

I’ve cheated in school when I thought that I could get away with it. I’m not proud of it and I don’t usually feel very good about myself afterwards, but sometimes it’s the only way possible to survive in a pressure cooker. My parents are really set on my getting good grades. They study my report card the same way they examine the newspaper’s stock market page. And they make me feel that I’ve got to live up to their expectations. But often it’s like each teacher acts as if his is the only subject we have. They think nothing of piling on our homework or giving surprise quiz17．实验室利用下列装置可以制取某些气体，请据图回答问题：（1）这五个装置示意图中，有一个装置是错误的，其中错误装置是E （填序号）．（2）图示中仪器①的作用加热；实验室用高锰酸钾来制取氧气，可以选择A作发生装置，但要对A装置进行改进，改进的方法是在试管口塞一团棉花；实验室若用B装置制取氧气，则该反应的文字表达式为过氧化氢$\stackrel{二氧化锰}{→}$水+氧气．（3）装药品之前，如何检查A装置的气密性？（4）乙炔又称电石气，是一种无色、无味、密度比空气略小、不溶于水的气体；工业上常用它燃烧产生的高温来切割和焊接金属；实验室用电石（固体）与水反应制取乙炔．你认为制取乙炔应选择的发生装置是B；收集装置是D．（5）装置A、B都可以用来制取氧气，比较这两个装置的不同，则B装置的优点是不用加热．（6）已知氧气的密度为1.429g/L，氮气的密度为1.251g/L，试计算空气中氧气与氮气的质量比．