问题 选择题

以铬酸钾为原料,电化学法制备重铬酸钾的实验装置示意图:

下列说法不正确的是(  )

A.在阴极区,发生的电极反应为:2H2O+2e-═2OH-+H2

B.在阳极区,通电后溶液逐渐由黄色变为橙色,是因为阳极区H+浓度增大,使平衡2Cr

O-4
+2H+Cr2
O2-7
+H2O向右移动

C.该制备过程总反应的化学方程式为:4K2CrO4+4H2O

 通电 
.
 
2K2Cr2O7+4KOH+2H2↑+2O2

D.测定阳极液中K和Cr的含量,若K与Cr的物质的量之比为d,则此时铬酸钾的转化率为α=

d
2

答案

A、根据题意可知:电极均为惰性电极,在阴极室,水得电子变成氢气,电极反应为:2H2O+2e-=2OH-+H2↑,故A正确;

B、阳极室水失去电子,电极反应为:2H2O-4e-=4H++O2↑,使阳极区氢离子浓度增大,平衡右移,故B正确;

C、总制备方程式为4K2CrO4 +4H2

 电解 
.
 
2K2Cr2O7 +4KOH+2H2↑+O2↑,故C正确;

D、设加入反应容器内的K2CrO4为1mol,反应过程中有xmol K2CrO4转化为K2Cr2O4,则阳极区剩余K2CrO4为(1-x)mol,对应的n(K)=2(1-x)mol,n(Cr)=(1-x)mol,生成的K2Cr2O4

x
2
mol,对应的n(K)=xmol,n(Cr)=xmol,根据:K与Cr的物质的量之比为d,解得x=2-d,转化率为
2-d
1
×100%
=2=d,故D错误;

故选D.

阅读理解

阅读理解。

      

     Have you ever thought about keeping a pet goldfish? First you need to know how to keep it.     

     Get a fishbowl      

     First get a fishbowl. Make sure the fishbowl is large enough for the goldfish to swim in. You should

 keep the fishbowl clean. Don' t clean the fishbowl with soap. Hot water will clean it well.     

     Feed a goldfish       

     Goldfish eats almost any food. And you can also buy some special food for your goldfish in shops. Do

 not feed it too much food. Feed it as much as it can eat in three minutes one time.      

     Keep the water clean     

     Dirty water is not good for the health of the goldfish. If the water is dirty, the goldfish will easily 'get 

 sick and may die. Change 25% of the water at least once a week. Never change all of the water because 

 it includes something that your goldfish needs.      

     As you can see, keeping goldfish as pets is  not difficult.

1. When you choose a fishbowl, you should think about the _____ of it.

    A. size                  

    B. color

    C. shape                  

    D. height

2. What's the meaning of the underlined word "die"?

    A. 康复                    

    B. 长大

    C. 厌恶                      

    D. 死亡

 3. You can't _____ according to the  passage.

    A. feed the goldfish some special food

    B. give it as much food as possible one time

    C. use hot water to clean the fishbowl

    D. change part of the water on time

4. Which of the following points is NOT mentioned in the passage?

    A. Getting a fishbowl.

    B. Feeding a goldfish.

    C. Choosing a goldfish.

    D. Keeping the water clean.

5. The writer thinks that it is _____ to keep a goldfish.

    A. cheap                  

    B. easy

    C. expensive            

    D. difficult

单项选择题