问题 填空题

铜是生物体必需的微量元素,也是人类最早使用的金属之一。铜的生产和使用对国计民生各个方面都产生了深远的影响。

(1)写出铜与稀硝酸反应的化学方程式:________________________________________________________________________________________________________________________________________________。

(2)为了保护环境和节约资源,通常先用H2O2和稀硫酸的混合溶液溶出废旧印刷电路板中的铜,最终实现铜的回收利用。写出溶出铜的离子方程式:________________________________________________________________________________________________________________________________________________。

(3)工业上以黄铜矿为原料,采用火法熔炼工艺生产铜。该工艺的中间过程会发生反应:2Cu2O+Cu2S6Cu+SO2↑,该反应的氧化剂是______________;当生成19.2 g Cu时,反应中转移的电子为__________mol。

(4)铜在潮湿的空气中能发生吸氧腐蚀而生锈,铜锈的主要成分为Cu2(OH)2CO3(碱式碳酸铜)。试写出上述过程中负极的电极反应式:________________________________________________________________________________________________________________________________________________。

(5)研究性学习小组用“间接碘量法”测定某试样CuSO4·5H2O(不含能与I反应的氧化性杂质)的含量。取a g试样配成100 mL溶液,每次取25.00 mL,滴加KI溶液后有白色碘化物沉淀生成。写出该反应的离子方程式:___________________________。继续滴加KI溶液至沉淀不再产生,溶液中的I2用硫代硫酸钠标准溶液滴定,发生反应的化学方程式为I2+2Na2S2O3=2NaI+Na2S4O6,平均消耗c  mol/L的Na2S2O3溶液V mL。则试样中CuSO4·5H2O的质量分数为______________。

答案

(1)3Cu+8HNO3(稀)=3Cu(NO32+2NO↑+4H2O

(2)Cu+H2O2+2H=Cu2+2H2O

(3)Cu2O和Cu2S 0.3

(4)2Cu+4OH+CO2-4e=Cu2(OH)2CO3+H2O

(5)2Cu2+4I=2CuI↓+I2 ×100%

(2)H2O2在酸性条件下能将Cu氧化为Cu2。(3)该反应中Cu2S和Cu2O中Cu的化合价均由+1价降低为Cu中的0价,Cu2S和Cu2O均为氧化剂,硫元素化合价由-2价升高到+4价,转移电子数为6个,故生成0.3 mol Cu时转移电子为0.3 mol。(4)Cu在负极失去电子形成Cu2,Cu2再与空气中的CO2、H2O 结合生成铜锈。(5)根据电子守恒得关系式:Cu2I2~Na2S2O3,故试样中CuSO4·5H2O的质量分数为×100%=×100%。

单项选择题
单项选择题

Is test anxiety destructive. Can we make test anxiety work for us The answer to both of these questions is yes. Test anxiety often interferes with student performance but this same test anxiety, if channeled correctly, can help improve performance.
In order to lessen the destructive elements of test anxiety, the approach should be to develop improved confidence and knowledge. As your knowledge of the course material increases, your confidence in your ability to succeed will increase. As your confidence increases, your anxiety will go down, allowing your knowledge to come through more efficiently. The way you prepare for a test can reduce anxiety during the test.
You will be surprised how confident you will feel if you know the material. Studies of memory show if you want to be able to recall information from text or lecture you have to review that material several times. It is important to know your own abilities and operate accordingly. If you know that you learn best by listening, prepare a tape of significant material and listen to the tape.
Study partners or study groups are often useful for self-testing. Experience in stressful situations tends to lessen anxiety in those situations. One way to help yourself retrieve material is through the use of mnemonic codes. Learn a code that lets you remember complex material. Developing an outline for an essay question that you know will be on the test or memorizing a formula are forms of code development.
Students are often frustrated by the sheer volume of material that has to be studied in college. Many instructors conduct reviews, give hints, identify what is important to study, use handouts or overhead transparency outlines. These materials should be at the top of your study list. If the instructor took the time to identify them, you should assume that they will play an important part of the test. While knowledge acquired during test preparation can help reduce anxiety, it is another thing to take the test itself. Following are a few suggestions to help reduce anxiety during the test.
When I arrive at a test, I often find students flipping text pages at the last minute trying to cram it all in at the end. You would be better off trying to relax, meditating a little, and clearing your mind to allow yourself the ability to concentrate on the questions that are coming.
As soon as the instructor gives you the signal to start, dump out formulas, codes, outlines from your memory onto the test answer sheets so that you will not have to worry about whether you will remember the codes long enough until you get to the appropriate test question.
You can build your confidence if you go through the test and answer all of the questions that you know first. Go back and work on those questions that need greater analysis, or that need to be worked out or need to be guessed at and your anxiety will not kick in until later in the test.
For those of you whose anxiety increases as study and preparation increase, your goal should be to start concentrating on things that take your mind off the test, i. e. , television, books, hobbies, movies, etc. Meditation and aerobic exercise have proven to be very useful methods for reducing undesirable effects of stress.
The solution to reducing the destructive influences of stress is to plan to study. Map out a schedule of when you will study each day. Identify the specific topics that you will study each day. Identify the areas of the material that you have had problems with and study those. Your plan should include reading the text material, reviewing notes and homework assignments, identifying material that needs further explanation, developing codes for memory material and testing yourself. Once you have studied adequately, your confidence will be fairly high, your knowledge will be satisfactory to do well on the test and the stomach butterflies will help you focus on the task at hand.
I’d wish you good luck on finals, but you and I both know that the more effectively you study, the luckier you will get.

What is the relationship between knowledge and confidence and test anxiety

A.As your knowledge of the course material increases, your confidence in your ability to succeed will increase.

B.As your test anxiety increases, your knowledge and confidence will increase.

C.As your confidence increases, your anxiety will go down, allowing your knowledge to come through more effectively.

D.Both A and