问题 填空题

下面是用98%的浓H2SO4(ρ=1.84g/cm3)配制成0.5mol/L的稀H2SO4 500ml的操作,实验操作如下,请把正确操作步骤(用1,2,3…表示)的序号填入括号内,并填写有关的空格:

______将配好的稀硫酸倒入试剂瓶中,贴好标签;

______盖好容量瓶塞,反复颠倒摇匀;

______用量筒量取______ml的98% 的浓硫酸;

______将______沿烧杯内壁慢慢注入盛有少量______的烧杯中;

______用少量蒸馏水洗涤烧杯2~3次,并将洗涤液也全部转移到容量瓶中;

______将已冷却至室温的硫酸溶液沿玻璃棒注入______;

______改用______   逐滴加蒸馏水,使溶液的______ 正好跟刻度相平.

______继续向容量瓶中加蒸馏水,直到液面接近刻度线1~2cm处;请回答:

若在操作中没有把少量蒸馏水洗涤烧杯的洗涤液全部转移到容量瓶中,会使稀硫酸溶液的浓度______(填“大于”、“小于”或“等于”) 0.5mol/L,配制成稀H2SO4时若加蒸馏水超过了刻度线,倒出一些溶液,再重新加蒸馏水到刻度线,会使稀硫酸溶液的浓度______(填“大于”、“小于”或“等于”) 0.5mol/L.

答案

浓H2SO4的物质的量浓度c=

1000×1.84×98%
98
mol/L=18.4mol/L,根据稀释定律,稀释前后溶质的物质的量不变,来计算浓硫酸的体积,设浓硫酸的体积为xmL,所以xmL×18.4mol/L=500mL×0.5mol/L,解得:x≈13.6,所以应量取的浓硫酸体积是13.6mL.

配制步骤有量取、稀释、移液、洗涤、定容、摇匀等操作,一般用量筒量取(用到胶头滴管)13.6mL浓硫酸,在烧杯中稀释,将浓硫酸沿烧杯内壁慢慢注入盛有少量水的烧杯中,边加边用玻璃棒搅拌,冷却后转移到500mL容量瓶中,并用玻璃棒引流,洗涤烧杯、玻璃棒2~3次,并将洗涤液也全部转移到容量瓶中,向向容量瓶中加蒸馏水,当加水至液面距离刻度线1~2cm时,改用胶头滴管滴加,使溶液的凹液面正好跟刻度相平,盖好容量瓶塞,反复颠倒摇匀,将配好的稀硫酸倒入试剂瓶中,贴好标签、贮存.

若操作中没有把少量蒸馏水洗涤烧杯的洗涤液全部转移到容量瓶中,由于烧杯沾有少量硫酸,移入容量瓶内的硫酸减小,所配溶液浓度小于 0.5mol/L,配制成稀H2SO4时若加蒸馏水超过了刻度线,配制溶液的体积偏大,所配溶液的浓度偏低,倒出一些溶液,再重新加蒸馏水到刻度线,会使稀硫酸溶液的浓度更低,故小于0.5mol/L.

故答案为:(8)、(7)、(1)、13.6、(2)、浓硫酸、水、(4)、(3)、500mL容量瓶、(6)、胶头滴管、凹液面、(5)、小于、小于.

阅读理解

Our cat has a sweet nature, and she can let us know what she wants. When we fail to meet her needs, she gently leads us in the proper direction. When I forget to fill her water bowl early in the morning, she runs after my legs, and then pushes me in the direction of her bowl. She doesn’t get irritated (生气的); instead, she expresses her wishes in the best way. And I always understand what she is telling me.

One day I found myself envying her simple expression. How many times had I expected my husband or my children to know my wants without my ever giving voice to them? How many times had I been disappointed that they couldn’t understand when I needed a hug, a compliment or a chocolate bar?

After a pleasant afternoon with my husband, I wanted to stop somewhere nice and have dinner, but he didn’t understand my hints (暗示). “Couldn’t you see that I wanted to go out to dinner?” I complained when he pulled into our driveway.

“Why didn’t you say so? I can’t read your mind,” he answered in impatience. His words gave me pause. Had I expected him to read my mind? Why hadn’t I expressed my desire more clearly? I realized I had fallen into the female trap of “If you love me, you can read my mind.”

Now, I state my needs clearly and directly. I look at my cat and know she agrees.

1. Why was the author disappointed in her husband or her children?

A. Her husband didn’t give her a hug.       B. Her children didn’t give her a chocolate bar.

C. They didn’t give her a compliment.       D. They didn’t understand her mind.

2. What will the author do if she wants something from her husband now?

A. She will give him her hints.            B. She lets him guess what she wants.

C. She tells him her needs directly.        D. She buys what she wants herself.

3. What can we learn from the underlined sentence in the fourth paragraph?

A. I realized what I did was wrong.      B. My husband stopped me from saying something.

C. I stopped and didn’t go with my husband.  D. My husband prevented me from going on.

4. What would be the best title of the text?

A. How does a cat ask for something?  B. Learn how to read your cat’s mind

C. A lesson from a cat               D. Guess what others think

问答题 简答题