问题 问答题

中学常见反应的化学方程式是A+B→X+Y+H2O(未配平,反应条件略去),其中A、B的物质的量之比为1:4.请回答:

(1)若Y是黄绿色气体,则Y的电子式是______,该反应的化学方程式是______.

(2)若A为非金属单质,构成它的原子核外最外层电子数是次外层电子数的2倍,B的溶液为某浓酸,则反应中氧化剂与还原剂的物质的量之比是______.

(3)若A为金属单质,常温下A在B的浓溶液中“钝化”,且A可溶于X溶液中.

①A元素在周期表中的位置是______(填所在周期和族);Y的化学式是______.

②含a mol X的溶液溶解了一定量A后,若溶液中两种金属阳离子的物质的量恰好相等,则被还原的X是______ mol.

(4)若A、B、X、Y均为化合物.向A溶液中加入硝酸酸化的AgNO3溶液,产生白色沉淀;B的焰色为黄色.则A与B按物质的量之比1:4恰好反应后,溶液中离子浓度从大到小的顺序是______.

答案

(1)因黄绿色气体为氯气,氯原子最外层7个电子,则氯气中存在一对共用电子对,其电子式为

,A、B的物质的量之比为1:4,

则反应为MnO2+4HCl(浓)

  △  
.
 
 MnCl2+Cl2↑+2H2O,故答案为:

;MnO2+4HCl(浓)

  △  
.
 
 MnCl2+Cl2↑+2H2O;

(2)A为非金属单质,构成它的原子核外最外层电子数是次外层电子数的2倍,若为2个电子层,则第一层电子数为2,第二层电子数为4,其质子数等于电子数等于6,即A为碳元素,A、B的物质的量之比为1:4,则该反应为碳与浓硝酸反应,其反应为C+4HNO3═CO2↑+NO2↑+H2O,由化合价可知碳元素的化合价升高,则碳作还原剂,硝酸中氮元素的化合价降低,则硝酸作氧化剂,由化学计量数可知氧化剂与还原剂的物质的量之比为4:1,故答案为:4:1;   

(3)A为金属单质,常温下A在B的浓溶液中“钝化”,则A为铁或铝,B为浓硫酸或浓硝酸,又A可溶于X溶液中则A为铁,由A、B的物质的量之比为1:4,该反应为铁与稀硝酸反应生成硝酸铁、一氧化氮和水;

①铁为26号元素,在在元素周期表中的第4周期Ⅷ族,铁与稀硝酸反应生成的Y为NO,故答案为:第4周期Ⅷ族;NO;

②设被还原的硝酸铁的物质的量为x,则

2Fe3++Fe═3Fe2+

 2         3

 x         

3x
2

由溶液中两种金属阳离子的物质的量恰好相等,则a-x=

3x
2
,解得x=0.4a,故答案为:0.4a;

(4)向A溶液中加入硝酸酸化的AgNO3溶液,产生白色沉淀,则A中含有氯离子,B的焰色为黄色,则B中含有钠元素,A与B按物质的量之比1:4恰好反应,则该反应为氯化铝与氢氧化钠的反应,其反应为AlCl3+4NaOH=3NaCl+NaAlO2+2H2O,显然若A与B的物质的量分别为1mol、4mol,则钠离子4mol,氯离子3mol,偏绿酸根离子略小于1mol,因偏铝酸根离子水解则溶液显碱性,即c(OH-)>c(H+),则离子大小为c(Na+)>c(Cl-)>c(AlO2-)>c(OH-)>c(H+),故答案为:c(Na+)>c(Cl-)>c(AlO2-)>c(OH-)>c(H+).

阅读理解

阅读理解。

      When you speak, write a letter, or make a telephone call, your words carry a message. People

communicate (交流) with words. But do you know people also communicate without words? A smile

on your face shows you are happy or friendly. Tears (眼泪) in your eyes tell others that you are sad.

When you raise your hand in class, the teacher knows you want to say something or ask questions.

You shake (摇) your head and people know you are saying "No". You nod(点头) and people know

you are saying "Yes".

      Other things can also carry messages. For example, a sign at the bus stop helps you to know which

bus to take. A sign on the wall of your school helps you to find the library. Signs on the doors tell you

where to go in or out. Have you ever noticed(注意) that there are a lot of signs around you and that

you receive messages from them all the time?

       People can communicate in many other ways. An artist(艺术家) can use his drawings to tell about

beautiful mountains , the blue seas and many other things.

Books are written to tell you about all the wonderful things in the world and what other people are

thinking about.

1. People communicate mainly (主要) with ______.

A. words  

B. singing  

C. signs and drawings  

D. wonderful things

2. If you want to say something or ask questions in class, you need to______.

A. shake your head  

B. shake hands  

C. put up your hand  

D. nod

3. People also receive______ from signs.

A. letters  

B. messages  

C. ideas    

D. books

4. Storybooks, TV, radio and films can help us to know______.

A. what is going on in the world.

B. where to find the library

C. what other people are thinking about

D. both A and C

5. The story tells us______.

A. why we smile  

B. which bus we should take

C. the ways we communicate  

D. why books are written

单项选择题