问题 问答题

如图所示,试管内盛有少量稀盐酸.把一段镁条投入该试管中.

(1)可观察到的现象有:______;

(2)该实验证明了镁与稀盐酸的反应______(选填“吸收”或“放出”)热量,该反应的化学方程式为:______;

(3)若镁条与稀盐酸恰好完全反应,则反应后形成的溶液中,溶质是______,溶剂是______.

答案

(1)镁条和稀盐酸反应生成氯化镁和氢气,因此现象是的现象是镁条溶解、产生气泡,又因为此反应是放热反应,广口瓶中的气压增大,所以还可看到a液面降低b液面升高;

(2)a液面降低b液面升高说明广口瓶中的气压升高,气压升高是因为气体受热膨胀造成的,因此镁条和稀盐酸反应属于放热反应;镁条和稀盐酸反应生成氯化镁和氢气,反应的化学方程式是Mg+2HCl=MgCl2+H2↑;

(3)若镁条与稀盐酸恰好完全反应,则形成的溶液是氯化镁溶液,溶质是氯化镁,溶剂是水.

故答案为:

(1)镁条溶解、产生气泡、a液面降低b液面升高;

(2)放出;Mg+2HCl=MgCl2+H2↑;

(3)氯化镁;水.

阅读理解

阅读下列短文,从每个小题所给的选项中选出最佳答案。  

     Sixteen years ago a boy gave me an important gift.  It was a smile.      

     It was the early autumn of my first year at a middle school, and my old school was far away.  

As a result, no one knew who I was.  I was very lonely, and afraid to make friends with anyone. 

Every time I heard the other students talking and laughing, I felt my heart break. I couldn't talk with 

anyone about my problems.        

     Then one day, my classmates talked happily with their friends, but I  sat at my desk unhappily as

usual. At that moment, a boy entered the classroom. I didn't know who he was. He passed me and

then turned back. He looked at me, with a smile.

      Suddenly, I felt the touch of something bright and friendly. It made me feel happy, lively and warm.

That smile changed my life. I started to talk with other students and made friends. Day by day, I became

closer to everyone in my class. The boy with the lucky smile has become my best friend now.

      One day I asked him why he smiled, but he couldn't remember smiling at me!

       It doesn't matter because all the dark days have gone. I believe that the world is what you think it is.

If you think it lonely, you might always be alone. So smile at the world and it will smile back.

1. When did the writer get the gift? [ ]

A. When she was 16 years old.

B. After she made friends with the boy.

C. In her first year at a middle school.

D. After she became closer to everyone in her class.

2. Why was the smile an important gift? [ ]

A. Because the writer's old school was far away.

B. Because the writer didn't know who the boy was.

C. Because the smile didn't mean anything to the boy.

D. Because it made the writer feel happy, lively and warm.

3. Where does she now think her feeling of unhappiness came from? [ ]

A. From her old school.

B. From her parents.

C. From herself.

D. From her classmates at the new school.

单项选择题