问题 选择题

1L某溶液中含有的离子如下表

离子Cu2+Al3+NO3-Cl-
物质的量浓度(mol/L)11a1
用惰性电极电解该溶液,当电路中有3mol e-通过时(忽略电解时溶液体积的变化及电极产物可能存在的溶解现象),下列说法正确的是(  )

A.电解后溶液呈酸性

B.a=3

C.阳极生成1.5mol Cl2

D.阴极析出的金属是铜与铝

答案

A.当电路中有3mole-通过时,阳极首先发生2Cl--2e-=Cl2↑,有0.5mol生成Cl2,然后发生4OH--4e-=O2↑+2H2O,生成2molH+,阴极首先发生:Cu2++2e-=Cu,析出1molCu,然后发生2H++2e-=H2↑,生成0.5molH2,同时生成1molOH-,因n(H+)>n(OH-),则反应后溶液呈酸性,故A正确;

B.由溶液电荷守恒可知2c(Cu2+)+3c(Al3+)=c(NO3-)+c(Cl-),可求得c(NO3-)=4moL/L,即a=4,故B错误;

C.电解时阳极首先发生:2Cl--2e-=Cl2↑,然后发生4OH--4e-=O2↑+2H2O,生成Cl2和O2,故C错误;

D.由于离子放电顺序Cu2+>H+>Al3+,没有Al生成,故D错误.

故选A.

单项选择题
阅读理解

阅读理解。

     Let children learn to judge their own work. A child learning to talk does not learn by being corrected

all the time; if corrected too much, he will stop talking. He notices a thousand times a day the difference

between the language he uses and the language those around him use. Bit by bit, he makes the necessary

changes to make his language like other people's. In the same way, children learn to do all the other things without being taught to walk, run, climb, whistle, ride a bicycle…They compare their own performances

with those of more skilled people, and slowly make the needed changes. But in school we never give a

child a chance to find out his mistakes and correct them for himself. We do it all for him. We act as if we

thought that he would never notice a mistake unless it was pointed out to him, or correct it unless he was

made to. Let him work out, with the help of other children if he wants it, what this word says, what the

answer is to that problem, whether this is a good way of saying or doing this or not.

     If it is a matter in mathematics or science, give him the answer book. Let him correct his own papers. Why should we teachers waste time in such routine work? Our job should be to help the child when he

tells us that he can't find the way to get the right answer. Let the children learn what all educated persons

must some day learn, how to measure their own understanding, how to know what he does not know.

1.According to the passage, the best way for children to learn things is by ________.

A.listening to skilled people's advice

B.asking older people many questions

C.making mistakes and having them corrected

D.doing what other people do

2.Which of the following does the writer think teachers should NOT do?

A.Give children correct answers.

B.Allow children to mark mistakes.

C.Point out children's mistakes to them.

D.Let children mark their own work.

3.According to the writer, teachers in school should ________.

A.allow children to learn from each other

B.point out children's mistakes whenever they are found

C.correct children's mistakes as soon as possible

D.give children more book knowledge

4.The passage suggests that learning to speak and learning to ride a bicycle are ________.

A.different from learning other skills

B.the same as learning skills

C.more important than other skills

D.not really important skills