要鉴别己烯中是否混有少量甲苯，正确的实验方法是（ ）
A．先加足量的酸性高锰酸钾溶液，然后再加入溴水
B．先加足量溴水，然后再加入酸性高锰酸钾溶液
C．利用焰色反应，点燃这种液体，然后再观察火焰的颜色
D．加入四氯化碳，萃取，观察是否分层
A．己烯和甲苯均能使酸性高锰酸钾溶液褪色，先加足量的酸性高锰酸钾溶液，不能鉴别是否含甲苯，故A错误；
B．先加入足量的溴水，除去己烯，再用酸性高锰酸钾溶液检验甲苯，故B正确；
C．焰色反应是金属元素的性质，不能用来鉴别有机物，故C错误；
D．加入四氯化碳不能鉴别，二者均溶于四氯化碳，不分层，故D错误；
故选B．
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| Sarah came running in. "Look what l found." Over the top of the paper I was reading came a long object that caused me to 1 . It was a snake skin. "Isn't it 2 ?" said my wide-eyed seven-year-old. I stared at it thinking to myself that it really wasn't 3 beautiful, but I have learned never to appear uninterested 4 tired of children. " 5 does a snake shed its skin?" Sarah asked. I also try to seize every 6 to teach my children there is almost something beyond the obvious. "Snakes shed their skin because they 7 to renew themselves," I explained. As is so often the 8 in my family, the original subject leads to 9 and another, until we are discussing something quite 10 . "Why do they need to renew themselves?" Sarah asked. Robert replied humorously. "Because they don't like 11 they are and they want to be someone else." Sarah and I politely 12 her brother. "We often need to shed our skins," I said to my now 13 daughter. "This snake no longer needs this skin. Probably he doesn't think he looks as 14 in it as he once did. Like buying a new suit." Of course, I'm sure this explanation won't 15 naturalists (博物学家). But Sarah was understanding. As we 16 , I knew that she began to understand that renewal is part of 17 and see what we need to keep and what we need to 18 . I was careful to point out that this is a 19 process, not one to be forced. "Snakes don't peel off their skin when they feel like it," I explained. "It 20 as a natural result of their growth." "I see, Dad," said Sarah and jumped off my lap, grabbed the snake skin, and ran off. | ||||
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