题干

淑平同学在我市某食品厂生产的盒装饼干中,发现盒内有一小包东西,其上标有“干燥剂”、“主要成分是生石灰”、“请勿食用”等字样。为了提高自己的实验探究能力,淑平决定对这包干燥剂展开探究。
(1)她将这袋干燥剂全部倒入一定量水中,充分搅拌后,触摸杯壁,感觉有点热。将其过滤,得到白色沉淀物和滤液。
(2)联系到空气成分和CaO的性质,她对白色沉淀物的组成提出了以下假设:
假设1:是CaO和CaCO3的混合物
假设2:是Ca(OH)2和CaCO3的混合物
假设3:只有 CaCO3
假设4:只有Ca(OH)2
其中假设____(填序号)不合理,原因是____ (用化学方程式表示)
(3)为了判断其它几种假设的合理性,该同学继续进行实验:
①取少量沉淀物放入试管中,加入稀盐酸,有气泡产生,由此可否定假设____。
②为了得到最后结论,他再取少量沉淀物放在另一支试管中,加入少量水振荡,静置后,滴入酚酞试液,呈红色,说明只有假设②合理。
(4)从此,淑平同学明白了:
①“请勿食用”是因为该干燥剂吸水后具有____ 性且____热。
②该干燥剂吸水后会变质,变质后的物质可能是CaCO3。写出CaO变质生成CaCO3的最后一步反应化学方程式____ 
③空气中的水份、氧气等能引起食品变质。一般采用____(写出两种方法)等包装方法可以防止或延缓食品变质。

上一题 下一题 0.0难度 选择题 更新时间:2018-10-19 11:29:26

答案(点此获取答案解析)

\u2460,CaO+H2O\u2550Ca\uff08OH\uff092,\u2463,\u78b1,\u653e,Ca\uff08OH\uff092+CO2

同类题3

阅读理解

    Why do we read poetry? First obvious one: because we enjoy it. The only other reason is for academic purposes, and that's not why this is here.

    Many of us read poetry simply because we often feel depressed and hopelessly lost, and in poetry we see how beautiful and strange everything is. So in that way poetry calms our anxiety.

    There are many different kinds of poems. They are not all calming. Some poems make me anxious, angry, scared, and sad, which is why I value them. As a reader, I want a full meal, not just dessert. I want the sweet and the bitter. Often, I read poetry when I'm already relaxed. In fact, I read more when I'm not stressed out.

    Here are the main reasons I respond to poetry, as far as I can tell. Metrical(格律的) poems are about setting up rules and then bending them. Usually, this is done by setting up a rhythm and then violating it or almost violating it. And then returning to it again. This satisfies my desire for order and also my desire for testing boundaries.

    Poetry plays with language and often slams words together in surprising ways, which is thrilling the way food can be when the chef has paired ingredients you never thought would taste good together but somehow do.

    Many poems are dense. Words mean two or three things at once and lots of suggestions are packed between the lines. This is intellectually inspiring and it allows me to read the same poem over and over always finding new things in it.

    And, of course, there's the subject matter. It interests me just as it would if the same subject was explored in a story or essay. Not all poems interest me in this way, but then not all stories and essays do, either.

根据短文内容,选择最佳答案,并将选定答案的字母标号填在题前括号内。