问题 选择题

下列有关实验的表述中,错误的是(  )

A.除去乙醇的水:加新制生石灰,蒸馏,收集馏出物

B.检验淀粉的水解产物:在用酸作催化剂的水解液中直接加入新制Cu(OH)2溶液,然后加热,观察是否有红色沉淀生成

C.除去乙酸乙酯中的乙酸:加饱和碳酸钠溶液,充分振荡,分液,弃水层

D.银氨溶液的配制:在洁净的试管中加2% AgNO3溶液1~2 mL,逐滴加入2%稀氨水,边滴边振荡,至沉淀恰好溶解时为止

答案

答案:B

题目分析:A、生石灰氧化钙极易吸水生成氢氧化钙,因此除去乙醇的水:加新制生石灰,蒸馏,收集馏出物即可,A正确;B、淀粉水解在酸性条件下进行,而醛基与新制氢氧化铜悬浊液的反应是在碱性条件下进行的,故B不正确;C、饱和碳酸钠溶液可以降低乙酸乙酯的溶解度,吸收乙酸,所以除去乙酸乙酯中的乙酸:加饱和碳酸钠溶液,充分振荡,分液,弃水层,C正确;D、在洁净的试管中加2% AgNO3溶液1~2 mL,逐滴加入2%稀氨水,边滴边振荡,至沉淀恰好溶解时为止,此时所得溶液是银氨溶液,D正确,答案选B。

单项选择题
单项选择题

For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never ending flood of words. In (1) a job or advancing in one, the ability to read and comprehend (2) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (3) readers. Most of us develop poor reading (4) at an early age, and never get over them. The main deficiency (5) in the actual stuff of language itself—words. Taken individually, words have (6) meaning until they are strung together into phrases, sentences and paragraphs. (7) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (8) words or passages. Regression, the tendency to look back over (9) you have just read, is a common bad habit in reading. Another habit which (10) down the speed of reading is vocalization—sounding each word either orally or mentally as (11) reads.
To overcome these bad habits, some reading clinics use a device called an (12) , which moves a bar(or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (13) the reader finds comfortable, in order to "stretch" him. The accelerator forces the reader to read fast, (14) word by word reading, regression and subvocalization practically impossible. At first (15) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (16) your comprehension will improve. Many people have found (17) reading skill drastically improved after some training. (18) Charlie Au, a business manager, for instance. His reading rate was a reasonably good 172words a minute (19) the training; now it is an excellent 1,378 words a minute. He is delighted that how he can (20) a lot more reading material in a short period of time.

A.reuse
B.reread
C.rewrite
D.recite