问题 问答题 简答题

常用的溶剂分为几类?请按极性大小顺序写出常用溶剂,并指出哪些溶剂能够互溶?

答案

参考答案:

常用溶剂可分为三类:

水、亲水性有机溶剂和亲脂性有机溶剂。

常见溶剂的极性度强弱顺序可表示如下:石油醚(PE.<四氯化碳(CCl4)<苯(Ben)<三氯甲烷(CHCl3)<乙醚(Et2O)<乙酸乙酯(EtOAC.<正丁醇(n-BuOH)<丙酮(Me2CO)<乙醇(EtOH)<甲醇(MeOH)<水(H2O),有机溶剂中甲醇、乙醇、丙酮为亲水性有机溶剂,其余为亲脂性有机溶剂。一般而言,水和亲水性有机溶剂可以混溶、有机溶剂之间也可以混溶。

阅读理解

根据短文内容,从下框的A—F选项中选出能概括每一段主题的最佳选项。选项中有一项为多余项.

A.Pay Attention to the Organization of an Article.

B.Check Your Understanding.

C.Lightning Speed Exercise

D.Set Aside Time Each Day.

E.Check Your Progress through Pacing

F.Speed up When Necessary.

小题1:______

Most of us can find 15 minutes or half an hour each day for some specific regular activity. For example, one famous surgeon always made it a rule to spend at least 15 minutes on general reading before he went to sleep each day. Whether he went to bed at 10 p.m. or 2:30 a.m. made no difference.

小题2:______

Nearly all ‘speed reading’ courses have a ‘pacing’ element---some timing device which lets the students know how many words a minutes he is reading. You can do this simply by looking at your watch every 5 or 10 minutes and noting down the page number you have reached.

小题3:______

Obviously there is little point in increasing your reading speed if you do not understand what you are reading. If you find you have lost the thread of the story, or you can’t remember clearly the details of what was said, re-read the section or chapter.

小题4:______

Take four or five pages of an interesting book you happen to be reading at the time. Read them as fast as you possibly can. Do not bother about whether you understand or not. After a ‘lightning speed’ of reading, you will usually find that your ‘normal’ speed has increased.

小题5:______

Most paragraphs in an article have a ‘topic sentence’ which expresses the central ideas. The opening paragraph often suggests the general direction and content of the piece, while paragraphs that follow expand or support the first. The closing paragraph often summarizes the very essence(实质) of what has been said.

多项选择题