问题 问答题

在下列几种简单的原电池中,按要求填空:

(1)将锌、铜用导线连接后共同浸入2mol/L的稀硫酸中,正极电极反应式为______,发生______反应(填氧化或还原);电子从______经外电路到______(填锌或铜),溶液中H+向______移动(填正极或负极),放电一段时间后,正极区pH值______(填变大、变小或不变).

(2)将铜片和铁片用导线连接后插入三氯化铁溶液中,也有电流通过电流表.画出该电池结构的示意图,在图上标出正、负极,电解质和电子流向

写出负极电极反应式为______,

总反应的离子方程式为______.

(3)将铁片和石墨电极用导线连接后插入氯化钠溶液中,也有电流通过电流表,请写出负极电极反应式______,正极电极反应式为______.

答案

(1)该原电池中锌是负极,铜是正极,正极上氢离子得电子生成氢气,发生还原反应;外电路上,电子从负极沿导线到正极,所以电子是从锌经外电路到铜;铜极附近有大量的电子,根据异性电荷相吸,铜极吸引氢离子,所以氢离子向正极移动;正极上氢离子得电子生成氢气,所以氢离子浓度降低,PH值变大.

故答案为:2H++2e-=H2↑;  还原;   锌;   铜;  正极;   变大.

(2)铁是负极,铜是正极,氯化铁是电解质,电子从负极(铁极)沿导线到正极(铜极).负极上铁失电子生成二价铁离子,正极上三价铁离子得电子生成二价铁离子,正负极上电极反应式相加得电池反应方程式.

故答案为:

Cu-2e-=Cu2+;   Cu+2Fe3+=Cu2++2Fe2+

(3)铁作负极,石墨作正极,溶液中溶有一定量的氧气,所以负极上铁失电子生成二价铁离子,正极上氧气和水得电子生成氢氧根离子.

故答案为:(-):2Fe-4e-=2Fe2+; (+):O2+4e-+2H2O=4OH-

问答题 案例分析题
单项选择题

Electronic mail has become an extremely important and popular means of communication.
The convenience and efficiency of electronic mail are threatened by the extremely rapid growth in the volume of unsolicited commercial electronic mail. Unsolicited commercial electronic mail is currently estimated to account for over half of all electronic mail traffic, up from an estimated 7 percent in 2001, and the volume continues to rise. Most of these messages are fraudulent or deceptive in one or more respects.
The receipt of unsolicited commercial electronic mail may result in costs to recipients who cannot refuse to accept such mail and who incur costs for the storage of such mail, or for the time spent accessing, reviewing, and discarding such mail, or for both. The receipt of a large number of unwanted messages also decreases the convenience of electronic mail and creates a risk that wanted electronic mail messages, both commercial and noncommercial, will be lost, overlooked, or discarded amidst the larger volume of unwanted messages, thus reducing the reliability and usefulness of electronic mail to the recipient. Some commercial electronic mail contains material that many recipients may consider vulgar or pornographic in nature.
The growth in unsolicited commercial electronic mail imposes significant monetary costs on providers of Internet access services, businesses, and educational and nonprofit institutions that carry and receive such mail, as there is a finite volume of mail that such providers, businesses, and institutions can handle without further investment in infrastructure. Many senders of unsolicited commercial electronic mail purposefully disguise the source of such mail.
Many senders of unsolicited commercial electronic mail purposefully include misleading information in the messages’ subject lines in order to induce the recipients to view the messages. While some senders of commercial electronic mail messages provide simple and reliable ways for recipients to reject (or "opt-out" of) receipt of commercial electronic mail from such senders in the future, other senders provide no such "opt-out" mechanism, or refuse to honor the requests of recipients not to receive electronic mail from such senders in the future, or both.
Many senders of bulk unsolicited commercial electronic mail use computer programs to gather large numbers of electronic mail addresses on an automated basis from Internet websites or online services where users must post their addresses in order to make full use of the website or service.
The problems associated with the rapid growth and abuse of unsolicited commercial electronic mail cannot be solved by the government alone. The development and adoption of technological approaches and the pursuit of cooperative efforts with other countries will be necessary as well.

Unwanted e-mail may ______.

A. cause companies to fail in business
B. cause wanted e-mail messages to lose
C. damage the credit of a company
D. do good to a small company