将10 g CO2和O2的混合气体，通过装有足量过氧化钠的干燥管，反

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问题选择题

将10 g CO₂和O₂的混合气体，通过装有足量过氧化钠的干燥管，反应后干燥管的总质量增加了5.6 g,则原混合气体中CO₂的质量分数为（）

A．32%

B．44%

C．56%

D．88%

答案

答案：D

反应前后固体质量差完全源自CO₂与Na₂O₂的反应,所以本题宜用“差量法”求解：

设其中CO₂的质量为x

2Na₂O₂+2CO₂====2Na₂CO₃+O₂Δm

88 56

x5.6 g

解得x="8.8" g

w(CO₂)=×100%=88%。

阅读理解

阅读理解。

Shu Pulong has helped at least 1,000 people bitten (咬) by snakes, "It was seeing people with snake bites

(伤口) that led me to this career," he said.

After his army service, Shu entered a medical school and later became a doctor of Chinese medicine. As

part of his studies he had to work in the mountains. There he often heard of people who had their arms and

legs cut off after a snake bite in order to save their lives.

Which of the following words can take the place of the word "career" in the first paragraph(段)?

A. conclusion

B. story

C. incident

D. job

填空题

在一个面积为16c㎡的正方形内，画一个最大的圆，这个圆的周长为______，面积为______．