问题 实验题

实验室用下图装置制取少量溴苯,填写下列空白。

(1)在烧瓶a中装的试剂是                            

(2)请你推测长直导管b的作用:

一是                    

二是                    的作用。

(3)导管c的下口出现白雾,原因是

                                                                 

(4)反应完毕后,向锥形瓶d中滴加AgNO3溶液有            生成,其离子方程式为                                         ;生成溴苯的化学反应方程式为                                     

(5)反应完毕后,将烧瓶a中的液体倒入盛有冷水的烧杯里,可以观察到烧杯底部有褐色不溶于水的液体,这可能是因为           的缘故。纯溴苯为无色液体,它比水______(轻或重)。获得纯净的溴苯应进行的实验操作是____________________________________________________________________

答案

(1)苯,铁粉,Br2 , (2)①导气   ②冷凝和回流(3)HBr易溶于水而形成酸雾

(4)淡黄色沉淀;    Br+  Ag+ = AgBr↓    

(5)溶有部分的Br2,重 用NaOH溶液洗涤后分液

题目分析:实验室制取溴苯是以苯、液溴为原料,用铁粉作还原剂(实质上起催化剂作用的是溴化铁)制取的。反应方程式为。故在烧瓶中应该装的试剂是苯、铁粉、Br2。该反应是放热反应,为减少液溴的挥发,所用的导管垂直于烧瓶的部分通常很长。这样长直导管b的作用一是导气,二是冷凝和回流。该反应是取代反应。除生成溴苯外,还产生HBr. HBr挥发,遇水蒸气形成氢溴酸小液滴而在导管c的下口出现白雾。HBr和AgNO3溶液反应产生溴化银淡黄色沉淀。离子方程式为Br+  Ag+ = AgBr↓。反应得到的溴苯是无色油状液体,不溶于水,密度比水大,但因为含有没反应的部分液溴,所以常常呈褐色或黄色。利用卤素与碱反应生成物容易溶解于水的特点除去。

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