问题 问答题

甲、乙、丙、丁四位同学在探究碱溶液与酚酞作用的实验时,发现了一个意外现象:氢氧化钠溶液滴入酚酞试液,溶液变成了红色,可是过了一会儿红色就消失了,这是什么原因呢?他们依据所学的化学知识,分别对这种意外现象的成因作了如下猜想:

甲:可能是氢氧化钠溶液与空气中的二氧化碳反应的缘故;

乙:可能是酚酞变质造成的;

丙:可能是酚酞与空气中的氧气反应,使红色消失;

丁:可能与氢氧化钠溶液的浓度大小有关.

(1)甲同学刚提出自己的猜想,就遭到其余三位同学的否定,三位同学的理由是______.

(2)丙同学认为乙同学的猜想也不正确,他的理由是______.

(3)四位同学讨论认为要验证丙同学的猜想,还需作如下实验,你知道其实验目的吗?

实验步骤设计这一步骤的目的
1.将配制的氢氧化钠溶液加热______
2.在加热后的溶液中滴入酚酞,并在

上方滴一些植物油

______
通过以上实验,四位同学观察到的现象是:溶液先变成红色,过了一会儿红色仍然消失.

(4)若丁同学的猜想正确,大家能设计实验证明吗?

实验方法可能观察到的现象和结论
____________

答案

(1)氢氧化钠溶液与空气中的二氧化碳反应生成的碳酸钠溶液也显碱性.故填:碳酸钠也呈碱性.

(2)开始时,氢氧化钠溶液滴入酚酞试液中溶液变成了红色,乙同学的猜想也不正确.故填:开始时,氢氧化钠溶液滴入酚酞试液中溶液变成了红色.

(3)①目的是为了除去溶液中的氧气.故填:除去溶液中的氧气.

②滴上植物油的目的是隔绝氧气.故填:隔绝氧气.

(4)设计的实验为:向褪色的溶液中加水稀释溶液又呈红色且不褪去.

阅读理解

I bought a jasmine(茉莉花)plant for my office. When I bought it, I was told it would bloom(开花)and the sweet smell would fill my office. I had the plant for two months, and every day I looked at it, but there weren’t any flowers or pleasant smell. I was not happy, so I gave the plant to my friend Linda.

One day, another friend Mary called and invited me to her office. When I walked in, her jasmine flowers surprised me. I reached out to touch the flowers. Mary cut some and gave them to me. I couldn’t help smelling them. Surrounded by the sweet smell of only a handful of these flowers, I suddenly understood something.

Mary bought her plant the same time I did. It took a year for her jasmine to bloom. I was so impatient for mine to bloom; regretfully, I gave it away.

In a way my life is like the jasmine plant. I need to be patient and let things happen.

Last Sunday Linda told me that she was going abroad the next week. Before she left, she returned the plant to me. This time I am going to wait. I have learned that when we want something in our life, we have to be patient. I am slowly learning to have that patience to wait for my jasmine to bloom.

小题1: Before she gave the jasmine away, the writer had it for.

A.one day

B.one year

C.two weeks

D.two months小题2: When the writer saw Mary’s jasmine, she felt _____.

A.unhappy

B.peaceful

C.hopeful

D.surprised小题3: What has the writer learned from her experience?

A.Patience is needed in life.

B.Flowers can make life better.

C.Friendship is necessary for us.

D.Jasmine can be a wonderful plant.

选择题