问题 填空题

(8分)铅蓄电池是最常见的二次电池,它是由两组平行排列的栅状铅合金极板作为主架,正极板上覆盖PbO2,负极板上覆盖Pb,电解质是硫酸。电池总反应式为:

Pb+PbO2+4H+2SO422PbSO4+2H2O

请回答下列问题:

(1)放电时:正极的电极反应式是__________________________;电解液中H2SO4的浓度将变____________;当外电路通过1 mol电子时,理论上负极板的质量增加______________g。

(2)在完全放电耗尽PbO2和Pb时,若按下图连接,电解一段时间后,则在A电极上生成____________、在B电极上生成____________,此时铅蓄电池的正负极的极性将____      _____。

答案

(1)PbO2 + 4H+ + SO42 + 2e= PbSO4 + 2H2O (2分)小(1分)  48(2分)

(2)Pb   PbO2  对换(各1分)

(1)放电相当于原电池,正极是得到电子的。所以根据总的方程式可知,正极反应式是PbO2 + 4H+ + SO42 + 2e= PbSO4 + 2H2O。根据总反应的方程式可知,放电是消耗硫酸的,因此硫酸的浓度是降低的;负极方程式是Pb+ SO42- 2e= PbSO4,所以外电路通过1 mol电子时,理论上负极板的质量增加0.5mol×96g/mol=48g。

(2)根据装置图可知,铅和电源的正极相连,作阳极,失去电子。而二氧化铅和电源的负极相连,作阴极,得到电子。所以A电极上生铅,B电极生成二氧化铅,因此此时铅蓄电池的正负极的极性将对换。

阅读理解

阅读理解。

   If you are a TV addict, you can't have missed the popular sitcom(情景喜剧) Home With Kids. The

lead characters, 17-year-old Xiao Xue and 14-year-old Liu Xing can remind us of our own behavior or

our classmates. We love the two teenagers, but are they good students? And what makes a good student?

"Being a student is a kind of occupation, so a good student should have good grades. Based on their

school reports, clever and diligent, Xiao Xue is a much better student than her brother, Liu Xing," says

Wu Hao, 16, Chifeng in Inner Mongolia. "The boy should work harder at studying since our duty as

students is to study well."

   It is generally accepted that getting good scores is crucial for a student. So to some, being a good

student means ranking high in your class or even your school. However, Wu also admits that a student's

personality is more important in being a role model student.

   "Honesty and kindness make you admirable. But Xiao Xue can be selfish, dishonest and arrogant,

which make others feel uncomfortable to be around her. So she has a lot yet to improve on," Wu said.

Many teenagers do not think it is fair to judge students by their grades. Take Liu Xing for example. He is

bright, good at computers and does everything else well like any other 14-year-old except studying.

  "He is smart, humorous and always has fancy ideas which makes him popular. I guess he could be an

excellent student if he attended school in the United States, where high grades are not so important and

creativity is hailed," says Jia Xiaoxu, 17, Hefei, Anhui.

    From the US hit movie High School Musical, Jia discovers her role model.

  "Gabriella in the movie is an ideal student. She is ranked top but is not seen as a bookworm. She is

sweet and sociable. Most importantly, Gabriella is always 'hungry' to try new things and actively

participates in different kinds of activities," she said.

1. What is the passage mainly about?

A. Two lovely middle school students.

B. A discussion about what makes a good student.

C. How to get high rank in study.    

D. Study and personality.

2. Which statement is NOT true according to Wu Hao?

A. A good grade is the most important for a good student.

B. A student's personality is more important for a role model student.

C. Xiao Xue still has some shortcomings which need to be improved.

D. Xiao Xue is much better in study than her brother Liu Xing.

3. Which of the following is NOT the advantage of Liu Xing according to the passage?

A. He is smart and humorous.      

B. He gets on well with Xiao Xue.

C. He does everything well except study.

D. He is good at computer and creative.

4. What can we learn from the last paragraph?

A. To be good students, we should be eager to learn and take part in different activities.

B. To be good students, we should work hard.

C. To be good students, we should not be addicted to books.

D. To be good students, we should only concern about social issues

单项选择题