把河沙(主要成分是SiO2)与镁按一定质量比(质量之比约为15∶24)混合均匀,

题型:实验题

问题:

把河沙(主要成分是SiO2)与镁按一定质量比(质量之比约为15∶24)混合均匀,装入试管中加热大约1 min后发生剧烈反应,生成一种白色固体化合物和一种硅化物,待生成的混合物冷却后放入盛有稀H2SO4的烧杯中,立即产生气泡并伴有爆炸声,产生的气体是一种能在空气中自燃的气态氢化物。

(1)写出河沙与镁粉在加热条件下的化学反应方程式:_________________________,该反应是_____________(填“放热”或“吸热”)。

(2)生成的混合物放入稀H2SO4中,产生的气体是_____________。

(3)写出产生“爆炸声”的化学反应方程式:_________________________________。

考点:化学实验的基本操作化学实验安全危险化学品的标志化学药品的变质
题型:实验题

有关作业管理的下述描述中,()是正确的。

A.系统现有空闲资源能满足被选作业的资源要求是选择作业进人主存的一个必要条件

B.作业与进程是一一对应的

C.作业调度选中一个作业后,与作业相关的进程就处于运行状态

D.在兼有批处理和分时的计算机系统中,往往把终端作业作为前台作业,把批处理作业作为后台作业

E.批处理作业是在输人井中等待处理的

题型:实验题

12分)有A B C D四种元素,A元素形成的-2价阴离子比氦原子的核外电子数多8,B 元素的一种氧化物为淡黄色固体,该固体遇到空气能生成A的单质,C为原子核内有12个中子的二价金属,2 .4C与足量热水反应时,在标准状况下放出气体2.24L ,DM层上7个电子。

(1)写出A的原子结构示意图:          B的离子结构示意图:          

(2)分别写出B D的最高价氧化物的水化物的化学式______,_______.

(3)用电子式表示BD形成的化合物的过程:                                

(4)C与D元素最高价氧化物的水化物反应的离子方程式                              

题型:实验题

_____ bad weather! We can't go to climb the mountains. [ ]

A. How

B. what a

C. what

D. How a

题型:实验题

In the second half of each year, many powerful storms are born in the tropical Atlantic and Caribbean seas. Of (91) , only about half a dozen (92) the p, circling winds of 75 miles per hour or more that give them hurricane status, and several usually (93) their way to the coast. There cause millions of dollars of (94) , and bring death to (95) numbers of people.
The great storms that hit the coast start (96) innocent circling disturbances hundreds, even thousands of miles out to sea. As they travel aimlessly over water (97) by the summer sun, they are carried westward by the (98) winds. When conditions are just (99) , warm, moist air flows in (100) the bottom of such a disturbance, moves upward through it and comes out at the top. In the (101) , the moisture in this warm air produces rain, and with it the heat is converted to energy in the form of p winds. As the heat increases, the (102) hurricane begins to swirl in a counter-clockwise motion.
The average life of a hurricane is only about nine days, but it contains almost (103) power than we can imagine. The energy in the heat released by a hurricane’s rainfall in a(n) (104) day would (105) the entire electrical needs of the United States for more than six months. Water, not wind, is the main (106) of death and destruction in a hurricane. A(n) (107) hurricane brings 6-to 12-inch downpours (108) in sudden floods. (109) is the powerful movement of the sea-the mountains of water moving toward the low-pressure hurricane center. The water level (110) as much as 15 feet above normal as it moves toward shore.

A.cooled

B.boiled

C.steamed

D.warmed

题型:实验题

在要害部门工作中如何正确认识和处理好重点和一般关系?

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