试题与答案

取一根用砂纸打磨干净的镁条和一个石棉网,将他们一起放在托盘天平上称量,然后在石棉

题型:问答题

题目:

取一根用砂纸打磨干净的镁条和一个石棉网,将他们一起放在托盘天平上称量,然后在石棉网上方将镁条点燃,镁条燃烧时发出耀眼的白光,产生大量白烟,再将镁条燃烧后的产物与石棉网一起放在托盘天平上称量,发现质量减轻了.有同学据此认为“质量守恒定律不是普遍规律”,这种说法对吗,为什么?

答案:

镁在空气中燃烧生成氧化镁,根据质量守恒定律,燃烧的镁的质量加上参加反应的氧气的质量等于生成的氧化镁的质量,但在实验过程中产生了大量的白烟,说明有些生成物散逸到空气中去了,称量的不是全部生成物的质量,故发现质量减轻了,但依旧遵循质量守恒定律.

故答案为:这种说法不对,因为有一部分生成物以白烟的形式散逸到空气中去了,称量的不是全部生成物的质量,故质量减少.

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题型:阅读理解

Music can be a great power (力量) to change people’s lives. Regina del Carmen Sanchez, 14, always believes this. The girl from Kansas City, US, leads a hard life. She lives in a small house with her mom and grandparents. Her mom gets a very low pay.

But it doesn’t stop Sanchez’s love of music. She wrote her first song Keep Your Head Up when she was 12. It described the bad situation(情况) at her home, but it also sent the message of hope: “My house is old and poor, but it beats (胜过) being homeless… Love yourself and never give up. You’ll see a better life if you keep your head up…”

It took Sanchez several months to finish the song. Sometimes during a break in class, when lyrics (歌词) came into her head, “I would have to write them down right then,” she told the local newspaper The Kansas City Star.

Jeremy Lillig was a spokesman for Bright Futures, a charity fund. When he saw the video of the song, he was moved. He shared it through social media (社交媒体). The fund has provided money for poor students in Kansas City.

Now Sanchez often plays the song in public. “I want to help people understand what is happening in the world in an easy way,” she said.

小题1:There are     people in Sanchez’s family.

A.three

B.four

C.five

D.six小题2: What’s true about Keep Your Head Up?  ______________________

A.It was written two years ago.

B.It showed a feeling of hopeless.

C.It described the good situation of a house.

D.It took Sanchez several weeks to write the song.小题3: The word “moved” can be replaced (代替) by   .

A.surprised

B.interested

C.touched

D.excited小题4: The best title of the passage can be    .

A.A girl and her song

B.Poor home is better than being homeless

C.Charity changes the girl’s life

D.Let’s support poor students.

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