问题 实验题

某研究性学习小组在网上收集到如下信息:钾、钙、钠、镁等活泼金属都能在CO2气体中燃烧。他们对钠在CO2气体中燃烧后的产物中的白色物质进行了如下探究:

实验:将燃烧的钠迅速伸入到盛满CO2的集气瓶中,钠在其中继续燃烧,反应后冷却,瓶底附着黑色颗粒,瓶壁上黏附着白色物质。

提出假设

假设1:白色物质是Na2O。

假设2:白色物质是Na2CO3

假设3:白色物质是Na2O和Na2CO3的混合物。

设计实验方案验证假设

该小组对燃烧后的白色产物

进行如下探究:

实验方案实验操作实验现象结论
方案1取少量白色物质于试管中,加入适量水,振荡,样品全部溶于水,向其中加入无色酚酞试液溶液变成红色白色物质为Na2O
方案2①取少量白色物质于试管中,加入适量水,振荡,样品全部溶于水,向其中加入过量的CaCl2溶液出现白色沉淀 
 ②静置片刻,取上层清液于试管中,滴加无色酚酞试液无明显现象
 

【思考与交流】

(1)甲同学认为方案1得到的结论不正确,其理由是       

(2)乙同学认为方案2得到的结论正确,白色物质为       

(3)通过方案1和方案2的实验,你认为上述三个假设中,       成立。你的理由是       

(4)钠在二氧化碳中燃烧的化学方程式为       

(5)丙同学认为白色物质有可能是氢氧化钠。你是否同意丙同学的观点?并简述理由:       

答案

(1)Na2CO3溶液也显碱性,会使酚酞试液变红

(2)Na2CO3

(3)假设2;方案2中②加酚酞试液无明显现象

(4)4Na+3CO22Na2CO3+C

(5)不同意,因为反应物中无氢元素(或违背质量守恒定律)

如下表。

 分析结论
(1)Na2CO3溶液显碱性,也会使酚酞试液变红方案1得到的结论不正确
(2)(3)方案2:①中出现的白色沉淀是CaCO3,所以白色产物中有Na2CO3存在;②中滴加无色酚酞试液无明显现象,说明白色产物中没有Na2O存在白色物质为Na2CO3
(4)反应物是Na、CO2,产物是Na2CO3和C4Na+3CO22Na2CO3+C
(5)因为反应物中无氢元素(或违背质量守恒定律)白色物质不可能是氢氧化钠
 

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.

12.().

A.waiting

B.stopping

C.standing

D.hearing

多项选择题