首先要通读全题,弄清实验目的,实验原理,然后运用所学知识大胆迁移,同时针对题干中信息准确细心答题,注重每个细节,特别提醒

(1)注意填写容量瓶时,需带容积规格

(2)化学用语的规范:如将溶液“褪色”写成“退色”、注意“褪色”与“变色”的差别、“坩埚”写成“坩锅”、“溶”与“熔”的差别、分液漏斗的“开关”应为“活塞”、气 体“跑掉”应为“逸出”等

(3)答题的规范性:如基本操作表达不完整(检查气密性、沉淀的洗涤、检验沉淀是否完全、焰色反应等);答题空泛、复杂而不切合题示信息;答题未找到根本原因,因果关系不明了等

(4)按要求填写“数字”或是“字母”,“偏高”或是“偏多”等

[例2-1]:凯氏定氮法测定奶粉中蛋白质含量的步骤如下:

① 样品处理:准确称取奶粉试样1.000 g置于烧瓶中,加入足量不含氮元素的试剂A,一定条件下充分反应,产物用水溶解并冷却后全部转移至100 mL容量瓶中定容。

② 碱化蒸馏:量取容量瓶中溶液10.00 mL转移至右图所示的反应管中,再加入足量NaOH溶液,塞好进样口橡皮塞。通入高温水蒸气。用吸收剂吸收产生的气体。

③ 滴定:向吸收气体后的溶液中滴加2滴指示剂,用0.01 mol/LHCl标准溶液滴定至终点。

已知:吸收剂中发生的反应为:NH3+4H3BO3=NH4HB4O7+5H2O;

滴定时发生的反应为:NH4HB4O7+HCl+5H2O=NH4Cl+4H3BO3

根据以上知识回答下列问题:

⑴    样品处理的目的是   ;通入高温水蒸汽的作用除加热外,还有    

⑵ 冷凝管的作用是冷凝、导气、    

⑶ 若蛋白质中氮元素的平均含量为16.0 %,滴定终点时消耗盐酸标准液15.50 mL,则该奶粉中蛋白质的含量为    %。

⑷ 凯氏定氮法测定奶粉中蛋白质含量灵敏度高,操作简单,缺点是   

1.  The Olympic Games, _____ in 776 BC., didn’t include women players until 1912.

A. first played           B. to be first played

C. first playing          D. to be first playing

2.    –I must apologize for _____ ahead of time.  –That's all right.

A. letting you not know      B. not letting you know

C. letting you know not      D. letting not you know

3.    –You were brave enough to raise objections at the meeting.

–Well, now I regret _____ that.

A. to do      B. to be doing  C. to have done   D. having done

4.    The salesman scolded the girl caught _____ and left her off.

A. to have stolen         B. to be stealing

C. to steal             D. stealing

5.    The first textbooks _____ for teaching English as a foreign language came out in the 16th century.

A. having written           B. to be written

C. being written           D. written

6.    The visiting minister expressed his satisfaction with the talks, _____ that he had enjoyed his stay here.

A. having added  B. to add    C. adding     D. added

7.    The patient was warned _____ oily food after the operation.

A. to eat not     B. eating not  C. not to eat  D. not eating

8.    –Can you spare me some time?  –I'm afraid not. I have lots of letters _____.

A. doing with   B. to do for    C. to deal   D. to deal with

9.    I can't understand _____ at that poor child.

A. you to laugh  B. you laughing C. you laugh   D. why laugh

10.   We must set about _____ our lesson for the mid-term examination.

A. reviewing   B. reviewed    C. to review   D. to reviewing

11.   I found John _____ the desk, _____ his homework carefully.

A. seated at; to do        B. sitting at; doing

C. sat at; does          D. taking his seat at; to do

12.   _____, he suddenly found the shop he was looking for.

A. When he turns round       B. To turn the left

C. Turned backward        D. Turning to the left

13.   Is this the watch you wish _____?

A. to have repaired        B. to repair it

C. to have it repaired        D. will be repaired

14.   This is the problem _____ at the next meeting.

A. to discussing           B. to be discussed

C. discussed     D. being discussed

15.   _____ many times, but he still couldn't understand it.

A. Having been told        B. Though he had been told

C. He was told          D. Having told

16.   It is considered no good _____ in the hotel.

A. recite  B. to be recited   C. recited     D. reciting

17.   With lost of trees _____, the house is not easily found.

A. to surround            B. surrounding

C. having surrounded        D. surrounded

18.   –Did you get your pay?

   –Yes, I remember _____. But I forget the exact amount.

A. paying    B. to be paid   C. being paid   D. having paid

19.   Many teachers were praised at the meeting, Mr. Zhou _____.

A. including  B. being included  C. to include  D. included

20.   I _____ the truth of your remarks, although they go against my interests.

A. cannot but admit        B. cannot but to admit

C. cannot but admitting      D. cannot help but admitting

21.   Professor Smith is said _____ another important discovery in chemistry.

A. having made  B. making    C. to have made   D. to make

22.   _____ by the appearance, he has just been frightened at the terrible news.

A. Judged     B. To be judged  C. Judging    D. Judge

23.They used what they had _____ for their daughter.

A. to buy a new dress       B. buying a new clothes

C. bought a new suit        D. buy a new clothing

24.I don't mind _____ the decision as long as it is not too late.

A. you to delay making      B. your delaying making

C. your delaying to make     D. you delay to make

25.The sale usually takes place outside the house, with the audience _____ on benches, chairs or boxes.

A. having seated          B. seating

C. seated              D. having been seated

 

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