问题 问答题

将水中的钙离子转化为草酸钙(CaC2O4)后进行反应与计算是测定水硬度的一种方法.下图是6.4g草酸钙固体在受热分解过程中所得固体产物的质量随温度变化的曲线,图中A、B、C分别代表三种固体.试利用图中信息结合所学的知识,回答下列问题:

(1)6.4g草酸钙A完全分解为碳酸钙B和CO时,生成的CO的质量是______g.

(2)当温度从500℃升至840℃时,为什么碳酸钙的质量保持不变______.

(3)试据图计算并推断C的合理化学式.

答案

(1)设生成CO的质量为x,CaCO3的质量为y,草酸钙分解为碳酸钙和CO的方程式为:

CaC2O4

 加热 
.
 
CaCO3+CO

128          100    28

6.4          y      x

128
6.4
=
100
y
=
28
x

解之得:x=1.4g   y=5g

∴生成CO的质量为1.4g.

(2)因为碳酸钙只有在高温下才分解,所以碳酸钙的质量保持不变.

(3)根据图可以看出生成C的质量为2.8g,又因为碳酸钙在高温时可分解为CaO和CO2,所以猜测C是氧化钙(CaO),验证如下:

 CaCO3

 高温 
.
 
CaO+CO2

  100         56

   5          2.8

∴固体C是氧化钙,化学式CaO.

单项选择题

"I was just like you--I’ thought I was invincible," says Adam Blomberg, standing before 400 students in a darkened auditorium at Miami’s Coral Reef Senior High School. A photo of a bloodied and unconscious teenager, a breathing tube protruding from his mouth, flashes on the wall.

"That was me," he says. There’s a collective gasp before the room grows silent and Blomberg,31, an anesthesiologist who trained at Brigham and Women’s Hospital in Boston, begins the story of what happened one night in February 1995.

He created a presentation illustrating the dangers of behaving irresponsibly in a car, from not buckling up to speeding to driving under the influence of alcohol and drugs. He tracked down photos of teen crash victims from the center’s archives, then incorporated statistics and his own experience. He spoke the first time to a local Boy Scout troop and was soon giving his talk, "A Survivor’s Story," at high schools around the state.

The Blomberg family had reason to celebrate. Adam had fully recovered and was on his way to fulfilling his lifelong dream of becoming a doctor. But in January 2000, Blomberg’s 22-year-old step-brother, Michael, was killed in a crash while driving to his Atlanta home late one night. He wasn’t wearing a seat belt. After the accident, Blomberg stopped telling his story to crowds, racked with guilt over his inability to reach Michael. If Blomberg had failed his own brother, he reasoned, how could he possibly make a difference to a roomful of strangers Requests from schools continued to roll in, but he turned down every one.

Then Blomberg got a call from a high school counselor. As he started into his standard excuse-lack of time—he looked across the room at a stack of thank-you notes from students who had heard him speak. He realized that kids needed to hear what he had to say. He agreed to visit the school and began contacting others on the waiting list for his talks.

Blomberg leaves the school hoping he has changed someone’s behavior. He recalls a letter he received from a student who heard him speak and got into a crash later that same day but was unharmed. " She told me she was wearing her seat belt because of me."

Letters like this reinforce his belief that he survived the accident for a reason. "There are a lot of physicians in the world, and we all save lives," he says. "I have a special opportunity to save lives not just as a doctor but also as a human being.\

Why did the author stop giving speeches for a while()

A. The death of his stepbrother makes him feel guilty

B. The development of seat belt avoided most accidents

C. There are no more requests from schools inviting him

D. He did not have enough time to give lectures at that time

单项选择题