问题 计算题

已知氯化铯的摩尔质量为168.5g/mol,其分子结构如图所示,氯原子(白点)位于立方体的中心,铯原子(黑点)位于立方体八个顶点上,这样的立方体紧密排列成氯化铯晶体。已知两个氯原子的最近距离为4×10-10 m,则氯化铯的密度为多少?

答案

解:1mol氯化铯的体积V=NAV0,1mol氯化铯的质量Mmol=168.5g

所以

单项选择题

Education is one of the key words of our time. A man, without an education, many of us believe, is an unfortunate victim of unfortunate circumstances deprived of one of the greatest twentieth-century opportunities. Convinced of the importance of education, modern states "invest" in institutions of learning to get back "interest" in the form of a large group of enlightened young men and women who are potential leaders. Education, with its cycles of instruction so carefully worked out, is punctuated by textbooks--those purchasable wells of wisdom what would civilization be like without its benefits

So much is certain: that we would have doctors and preachers, lawyers and defendants, marriages and births; but our spiritual outlook would be different. We would lay less stress on "facts and figures" and more on a good memory, on applied psychology, and on the capacity of a man to get along with his fellow-citizens. If our educational system were fashioned after its bookless past we would have the most democratic form of "college" imaginable. Among the people whom we like to call savages all knowledge inherited by tradition is shared by all; it is taught to every member of the tribe so that in this respect everybody is equally equipped for life.

It is the ideal condition of the "equal start" which only our most progressive forms of modern education try to reach again. In primitive cultures the obligation to seek and to receive the traditional instruction is binding on all. There are no "illiterates"--if the term can be applied to peoples without a script--while our own compulsory school attendance became law in Germany in 1642, in France in 1806, and in England in 1976, and is still non-existent in a number of "civilized" nations. This shows how long it was before we considered it necessary to make sure that all our children could share in the knowledge accumulated by the "happy few" during the past centuries. Education in the wilderness is not a matter of monetary means. All are entitled to an equal start. There is none of the hurry that, in our society, often hampers the fui1 development of a growing personality. There, a child grows up under the ever-present attention of his parents; therefore the jungles and the savages know of no "juvenile delinquency". No necessity of making a living away from home results in neglect of children, and no father is confronted with his inability to ’"buy" an education for his child.

It can be inferred from the text that()

A. some families now can hardly afford to send their children to school

B. everyone today has an equal opportunity in education

C. every country invests heavily in education

D. we are not very certain whether preachers are necessary or not

单项选择题