问题 计算题

造纸厂会产生含氢氧化钠的废水,需经处理呈中性后排放。为测定此废水中氢氧化钠的质量分数,工作人员取了40g废水样品加入到锥形瓶中,逐滴加入10%的稀硫酸,至恰好完全反应时,消耗稀硫酸49 g。计算废水中氢氧化钠的质量分数。

答案

n(H2SO4 )=49×10%g/98g/mol=0.05mol 。

设氢氧化钠物质的量xmol

H2SO4 + 2NaOH = Na2SO4 + 2H2O

1               2

0.05           x

1/2  = 0.05/x

x =0.1mol       

氢氧化钠的质量分数=×100%=10%

题目分析:依据题意可知,发生的反应是H2SO4 + 2NaOH = Na2SO4 + 2H2O,已知硫酸的质量为n(H2SO4 )=49×10%g/98g/mol=0.05mol,待求的是氢氧化钠的量,可根据方程式列出已知和未知的比例式求出,然后求出氢氧化钠的质量,再依据溶质质量分数的计算公式即可求解.

阅读理解

.

Dear Sir ,

I recently found your website of Chinese a very Culture a very good source .I am a professor teaching at Soochow University in Taipei Taiwan , and I would plan to quite often use some articles on your website for my coures of Introduction to Chinese Culture. Therefore, I’d like to inform you of educational purposes and hopefully to have your permission. Meanwhile, I do wish I could have more materials from your service. Much grateful to you.

Yours  sincerely,

Byron Gong

Dear Mr. Byron Gong,

It is pleasue to know that our websit has been of help for you to introduce Chinese culture in your class. Sharing the same mission in  promoting culture ,we are glad to grant you the permission in using the sourses of our website for your educational purposes, under the condition that all the sources are credited .However ,if the pictures or articles are to be used for publication, you can mail us and further discuss on that.

We are happy to provide you with some furthetr material, but we would like to know what kind of information would be of interest to you.

Thank you again for attention to our website .Any suggestion is welcome ,and we would appreciate your help if you could tell us what contents in our website are of most interest and significate to you and what parts shoud be given more attention.

Sincerely yours

Chinaculture .org

60. What is Mr. Byron Gong doing?

A. He is working for Soochow University in Taipei Taiwan as a cleaner.

B. He is nothing to do with Soochow University.

C. He is a professor teaching at  Soochow University.

D. He is searching for some scholars.

61. Why does  Mr. Byron Gong write the letter ?

A. He intends to introduce to his students if Chinese Culture is worth learing .

B. He asks for the permission from the website to use the material in his teaching.

C. He expects to be allowed to work in the group in the website.

D,He would like to inforn the website that he hopes to help then introduce Chinese culture.

62.What was the response of the website after they received the letter ?

A The wehsite responed to his letter coldly.

B. The wehsite responed to his letter in a polite and anxious way.

C. The website answered him enthusiasticaly,reasonably and suggestibly.

D. The website answered him eagerly.

63. What can we learn from the response of the website ?

A. They would be grateful to informed what contents are interesting and significant.

B. They wish to learn more about Mr. Byon Gong’s hobbies.

C. They expect to know more about their mistakes in the material.

D. They hope for his appreciation in return for the use of their material.

单项选择题