材料题
B
The famous director of a big and expensive movie planned to film a beautiful sunset over the ocean,so that the audience could see his hero and heroine(男女英雄)in front of it at the end of the film as they said goodbye to each other forever．He sent his camera crew(摄制组)out one evening to film the sunset for him．
The next morning he said to the men,“Have you provided me with that sunset ”
“No,sir,”the man answered．
The director was angry．“Why not ”he asked．
“Well,sir,”one of the men answered,“we’re on the east coast here,and the sun sets in the west．We can get you a sunrise over the sea,if necessary,but not a sunset．”
“But I want a sunset!”the director shouted．“Go to the airport,take the next flight to the west coast,and get one．”
But then a young secretary had an idea．“Why don’t you photograph a sunrise,”she suggested,“and then play it backwards Then it’ll look like a sunset．”
“That’s a good idea!”the director said．Then he turned to the camera crew and said,“Tomorrow morning I want you to get me a beautiful sunrise over the sea．”
The camera crew went out early the next morning and filmed a bright sunrise over the beach in the middle of a beautiful bay(海湾)．Then at nine o’clock they took it to the director．“Here it is,sir,”they said,and gave it to him．He was very pleased．
They all went into the studio．“All right,”the director explained,“now our hero and heroine are going to say goodbye．Run the film backwards so that we can see the‘sunset’behind them．”
The“sunset”began,but after a quarter of minute,the director suddenly put his face in his hands and shouted to the camera to stop．
The birds in the film were flying backwards,and the waves on the sea were going away from the beach．
One evening,the director sent his camera crew out．
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
