问题 问答题

东方中学课外活动小组在测定由氯化钠和硫酸钠形成混合物的组成时,进行了以下实验:取20g混合物全部溶于水,将得到的溶液等分为4份,然后分别加入一定量未知质量分数的氯化钡溶液,实验数据见下表:

第一份第二份第三份第四份
加入氯化钡溶液质量(g)15202530
反应得到沉淀的质量(g)1.401.862.332.33
若有关的化学反应为:Na2SO4+BaCl2=BaSO4↓+2NaCl,请计算:

(1)未知氯化钡溶液的质量分数为多少.

(2)原混合物中硫酸钠的质量分数是多少.(精确到0.01)

答案

设:25g未知质量分数的氯化钡溶液中所含氯化钡的质量分数为x,混合物中硫酸钠的质量分数为y.

Na2SO4+BaCl2=BaSO4↓+2NaCl

142        208     233

20g÷4×y  25g×x  2.33g

(1)

208
233
=
25g×x
2.33g
,x=8.32%

(2)

142
233
=
20g÷4×y
2.33
,y=28.4%

答:(1)未知氯化钡溶液的质量分数为8.32%.

(2)原混合物中硫酸钠的质量分数是28.40%.

阅读理解

Years ago, I lived in a building in a large city. The next building only was a few feet away from mine. They was a woman lived there, and I had never met her, yet I could see she sat by her window each afternoon, drinking or reading.

After a few months, I began to notice that her window was dirty. Everything was unclear through the dirty window. I would say to myself. “I wonder why that woman doesn’t clean her window. It really looks terrible.”

One sunny morning I decided to clean my house, including washing the window.

Late in the afternoon when I finished the cleaning, I sat down by the window with a cup of coffee for a rest. What a surprise! Across the way, the woman sitting by her window was clearly visible (看见). Her window was clean!

It dawned on me. I had been criticizing (批评) her dirty window, but all the time I was watching hers through my own dirty window.

That was quite an important lesson for me. How often had I looked at others through the dirty window of my heart?

Since then, whenever I wanted to judge (评判) someone, I asked myself first, “Am I looking at him through my own dirty window?” I try to clean the window of my own world so that I may see the world about me more clearly.

小题1: The writer couldn’t see everything clearly through the window because __________.

A.the woman’s window was dirty

B.the writer’s window was dirty

C.the woman lived nearby

D.the writer was near-sighted小题2: The writer was surprised that _________.

A.the woman was sitting by her window

B.the woman’s window was still terrible

C.the woman did cleaning in the afternoon

D.the woman’s window was clean小题3: “It dawned on me” probably means “_______”.

A.I began to understand it

B.it cheered me up

C.I knew it grew light

D.it began to get dark小题4: It’s clear that ________.

A.the writer had never met the woman before

B.the writer often washed the window

C.they both worked as cleaners

D.they lived in a small town小题5: From the passage, we can learn _______.

A.one shouldn’t criticize others very often

B.one should often make his windows clean

C.one must judge himself before he judges others

D.one must look at others through his dirty windows.

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