【简答题】xx中学初三化学兴趣小组设计了如图所示的实验装置来测定空气中氧气的含量.实验步骤是: ①检查装置的气密性;②用弹簧夹夹紧橡皮管;③点燃燃烧匙内的红磷;④将燃烧的红磷迅速插入瓶内,并把塞子塞紧;⑤燃烧完毕,冷却后打开弹簧夹分析探究 (l)实验中可观察到的现象是______;其原因是______由此可得出的结论是: ①______②______ (2)聪明的小明发现水的体积只占瓶容积的1/5,他立即得...
【单选题】What is said about the future citizens of the proposed space nation?
A.
They must be experts in space technology.
B.
Most of them will live in the space station.
C.
The number of citizens will be 150 million.
D.
They will help to launch the nation's first satellite.
【单选题】颐和园中的谐趣园又被称为“园中之园”,其中有三趣,即
【单选题】下面句子中主句的谓语是什么? 3What seems to be almost sure is the solutions to space travel and living in space will be found when the possibility of profit from development of technologies in and for space is seen...
【简答题】用来测定空气成分的方法很多,如图所示的是用红磷在空气中燃烧的测定方法.实验步骤如下: ①在集气瓶按体积分为5等份,做好标记. ②检查装置的气密性. ③在燃烧匙内装入足量的红磷,将导管上的止水夹夹紧,在酒精灯上点燃红磷,立即伸入集气瓶中塞紧橡皮塞. ④充分反应后,待集气瓶冷却至室温,打开止水夹. (1)写出步骤③化学反应的文字表达式为______. (2)实验完毕,若进入集气瓶中水的体积不到总容积的...