问题 问答题

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某小组同学在协助老师整理化学试剂时,发现一瓶标签残缺的无色液体(如图)(温馨提示:标签上的5%表示该混合物中主要成分所占的质量分数).他们对此瓶无色液体是什么产生了兴趣,于是进行了如下探究.

大胆猜想:猜想一:盐酸;猜想二:稀硫酸;猜想三:过氧化氢溶液.小组对标签又进行了仔细的观察、分析,他们一致认为猜想一不正确.理由是______.

设计方案:同学们结合所学知识设计出如下探究方案:

向盛有少量二氧化锰的试管中加入适量的该液体,并将带火星的木条放在试管口.

实验与事实:按上述方案进行实验,发现有大量气泡产生,带火星的木条复燃.

结论与解释:(1)以上事实证明猜想______是正确的;

(2)产生气体的反应可用化学方程式表示为______.反思与评价:为避免在今后的实验中出现标签残缺的情况,在倾倒液体时应注意______.

答案

根据破损标签的部分化学式可以知道,瓶内物质的化学式是H2X型,而盐酸是HCl,故不可能是盐酸,故填:盐酸的化学式是HCl,不是H2X型;

(1)向盛有少量二氧化锰的试管中加入适量的该液体,并将带火星的木条放在试管口,有大量气泡产生,带火星的木条复燃,说明生成了氧气,而硫酸不会生成氧气,过氧化氢会生成氧气,故猜想三是正确的,故填:三;

(2)过氧化氢在二氧化锰催化作用下能生成氧气和水,为避免标签被腐蚀,在倾倒液体时要将标签向着手心,故填:2H2O2

 MnO2 
.
 
2H2O+O2↑,倾倒液体时标签要向着手心.

单项选择题 A1型题
单项选择题

There are many kinds of friends. Some are always (1) you, but don’t understand you. Some say only a few words to you, but understand you. Many people will step in your life, but only (2) friends leave footprints.

I shall always recall the autumn and the girl with the (3) . She will always bring back the friendship between us. I know she will always be my best friend.

It was the golden season. I could see the yellow leaves (4) with the cool (5) . In such a season, I liked walking alone on the roads covered with leaves, (6) to the sound of them.

Autumn is a (7) season and life is uninteresting. The free clays always get me (8) . But one day, the sound of a violin (9) into my ears like a stream flowing in them ountains. I was so surprised that I jumped to see what it was. A young girl, standing in the wind, was (10) in playing her violin.

I had (11) seen her before. The music was so nice that I listened quietly. Lost in the music, I didn’t know that I had been (12) there for so long but my existence did not seem to disturb her.

Leaves were still falling. Every day she played the violin at the comer of the building (13) I went downstairs to watch her performance. I was the only listener. The autumn seemed no longer lonely and life became (14) . (15) we didn’t know each other, I thought we were already good friends. I believe she also loved me.

Autumn was nearly over. One day, when I was listening carefully, the sound suddenly (16) . To my astonishment, the girl came over to me.

"You must like music from the violin. " she said.

"Yes. And you play very well. Why did you stop" I asked.

Suddenly, a (17) expression appeared on her face and I could feel something unusual.

"I came here to see my grandmother, but now I must leave. I once played very badly. It was your listening every day that (18) me." she said.

"In fact, it was your playing (19) gave me a meaningful autumn," I answered, "Let’s be friends. "

The girl smiled, and so did I. I never heard her play again in my life. I no longer went downstairs to listen to her. Only thick leaves were left behind. But I will always remember the fine figure of the girl. She is like a (20) —so short, so bright, like a shooting star giving off so much light that makes the autumn beautiful.

13().

A.because

B.so

C.while

D.if