搜题请搜索小程序“爱下问搜题”
问题 选择题

将一定量的苯（C6H6）和氧气置于一个完全密闭的容器中引燃，反应后生成二氧化碳、水和一种未知物X．测得反应前后各物质的质量如下表：

物质苯氧气二氧化碳水X
反应前质量/g3.99.6000
反应后质量/g006.62.7m
下列判断正确的是（　　）

A．表中m的值为13.5

B．该反应属于分解反应

C．物质X中一定不含氢元素

D．该反应不符合质量守恒定律

答案

由表格信息可知反应后CO2质量增加了6.6g，是生成物；H2O质量增加了2.7g，是生成物；O2质量减少了9.6g，是反应物；苯的质量减少了3.9g克，是反应物；生成物还少4.2g，所以X是生成物．

A、反应后生成的物质x的质量4.2g，故m的值为4.2，故选项错误．

B、反应物是苯和O2，生成物是CO2、H2O和X，不是分解反应，故选项错误．

C、根据反应前后元素质量相等，苯中含氢元素的质量为3.9g×

6
78
×100%=0.3g，2.7g水中含氢元素的质量为2.7g×
2
18
×100%=0.3g，反应前后氢元素的质量相等，故物质X不含有氢元素．故选项正确．

D、该反应是化学变化，符合质量守恒定律，故选项错误．

故选C．

问答题

如图，一个三孔插座，其中有一个插孔的导线是与室外大地相连的，请把这个插孔与图中代表大地的记号E用线连起来．如果连这个插孔的导线断了，使用这个插座还能使洗衣机转动，但存在的问题是：______．
查看答案
单项选择题

Believe it or not，optical illusion can cut highway crashes.

Japan is a case in point．It has reduced automobile crashes on some roads by Rearly 75 percent using a simple optical illusion．Butst．ripes,called chevrons(人字形)，painted on ther rads make drivers think that they are driving faster than they really are，and thus drivers slow down.

Now the American Automobile Association Foundation for Traffic Safety in Washington D．C. is planning t。repeat Japan’s success．Starting next year，the foundati。n will paint cheyrons and。ther pattems of stripes on selected roads around the country to test how well the patterns reduce highway erashes．

Excessive(too great)speed plays a major role in as much as one fifth of all fatal traffic accidents， according to the foundation．To help reduce those accidents，the foundation will conduct its tests in areas where speed-related hazards(danger)are the greatest curves，exit slopes，traffic circles，and bridges．

Some studies suggest that straight，horizontal bars painted across roads can initially cut the average speed of drivers in half．However,traffic。ften returns to full speed within months as driVers become used to seeing the painted bars．

Chevrons，scientists say，not only give drivers the impression that they are driving faster than they reallv are but als0 make a lane appear to be narrower．The result is a longer lasting reduction in highway speed and the number of traffic accidents．

The passage mainly discusses（）

A．a new way of highway speed control

B．a new pattern for painting highways

C．a new way of training drivers

D．a new type of optical illusion
查看答案