问题 问答题

如图A-D是初中化学中的四个实验,请按要求填空:

(1)实验A中观察到的现象是______.

(2)写出实验B发生反应的化学方程式______.

(3)实验C中盛放白磷和红磷用的是铜片,这是利用铜片的______.

(4)实验D中燃烧匙中所盛药品为红磷,实验中红磷要过量,其原因是______.

答案

(1)因为二氧化碳的密度大于空气,所以下层的蜡烛先灭,故实验A中观察到的现象是:蜡烛由下至上依次熄灭;

(2)实验B为电解水的实验,则可书写其化学方程式为2H2O

通电
.
2H2↑+O2↑;

(3)实验C中盛放白磷和红磷用的是铜片,这是利用铜片的导热性;

(4)实验D中燃烧匙中所盛药品为红磷,实验中红磷要过量,其原因是:使瓶中的氧气能完全反应.

故答案为:

(1)蜡烛由下至上依次熄灭;(2)2H2O

通电
.
2H2↑+O2↑;

(3)导热性;(4)使瓶中的氧气能完全反应.

判断题
单项选择题

The standardized educational or psychological tests, that are widely used to aid in selecting, assigning, or promoting students, employees, and military personnel have been the target of recent attacks in books, magazines, the daily press, and even in Congress. The target is wrong, for in attacking the tests, critics divert attention from the fault that lies with ill-informed or incompetent users. The tests themselves are merely tools, with characteristics that can be measured with reasonable precision under specified conditions. Whether the results will be valuable, meaningless, or even misleading depends partly upon the tool itself but largely upon the user.

All informed predictions of future performance are based upon some knowledge of relevant past performance. How well the predictions will be validated by later performance depends upon the amount, reliability, and appropriateness of the information used and on the skill and wisdom with which it is interpreted. Anyone who keeps careful score knows that the information available is always incomplete and that the predictions are always subject to error.

Standardized tests should be considered in this context. They provide a quick, objective method of getting some kinds of information about what a person has learned, the skills he has developed, or the kind of person he is. The information so obtained has, qualitatively, the same advantages and shortcomings as other kinds of information. Whether to use tests, other kinds of information, or both in a particular situation depends, therefore, upon the empirical evidence concerning comparative validity, and upon such factors as cost and availability.

In general, the tests work most effectively when the traits or qualities to be measured can be most precisely defined (for example, ability to do well in a particular course of training program) and least effectively when what is to be measured or predicted cannot be well defined (for example, personality or creativity). Properly used, they provide a rapid means of getting comparable information about many people. Sometimes they identify students whose high potential has not been previously recognized, but there are many things they do not do. For example, they don’t compensate for gross social inequality, and thus don’t tell how able an underprivileged younger might have been had he grown up under more favorable circumstances.

The selection implies that, more often, the value of an educational test rests with()

A. the interpretation of test results

B. the analysis of the students tested

C. the skill and wisdom of the test itself

D. the accuracy of the information provided