问题 选择题

碱性电池有容量大,放电电流大的特点,被广泛应用。锌-锰碱性电池以氢氧化钾溶液为电解液,电池总反应式为:Zn + 2MnO2 + H2O=Zn(OH)2 + Mn2O3。下列说法错的( )

A.电池工作时,锌失去电子

B.电池正极的电极反应式为2MnO2 + H2O+2e-==Mn2O3 + 2OH-

C.外电路中每通过0.2mol电子,锌的质量理论上减少13g

D.电池工作时,电子由负极通过外电路流向正极

答案

答案:C

题目分析:原电池中较活泼的金属是负极,失去电子,发生氧化反应。电子经导线传递到正极,所以溶液中的阳离子向正极移动,正极得到电子,发生还原反应,所以根据反应的方程式可知,锌失去电子,A正确;二氧化锰在正极得到电子,B正确;1mol锌失去2mol电子,则外电路中每通过0.2mol电子,锌的质量理论上减少6.5g,C不正确;D正确,答案选C。

点评:该题是高考中的常见题型,属于中等难度的试题。试题基础性强,侧重对学生能力的培养和解题方法的指导与训练。该题的关键是明确原电池的工作原理,然后结合题意灵活运用即可。

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Over 60﹪of pupils in South African schools choose English for learning and teaching, but only 7﹪of pupils speak English as their home language, a recent South Africa survey shows.

Out of the country’s 12.2 million pupils only 851,536 speak English at home, yet 7.6 million pupils choose English as their favorite language of learning and teaching. Zulu is the most widely spoken home language, spoken by over 3.1 million pupils. However, less than a third of them choose to be taught in Zulu. The same thing is true of Pedi-speaking pupils, only a third of such pupils choosing to be taught in their home language. Besides English,

Afrikaans is the only language that has more pupils choosing it as their language of instruction than it has pupils who speak it at home. In primary schools, most pupils will choose African languages. As early as grade four, many would choose English or Afrikaans in their lessons.

The rising number of English-learning pupils is mainly caused by social and cultural reasons. English is the most common spoken language in official and public life in South Africa, the survey reports. In April 2011, the leaders of higher education and training said that they would take some steps to improve the university teaching and prevent the continuing decline of African languages. They suggested that in future every South African university student could be required to learn at least one African language in order to complete their studies at school.

小题1: We can learn from the passage that most South African pupils__________.

A.speak English both at home and at school

B.are required to learn two languages at school

C.choose English as their primary school language

D.are expected to speak their native language at home.小题2: It can be inferred from the passage that__________________.

A.Afrikaans is the most popular home language in South Africa

B.it’s easier for South African pupils to learn Afrikaans at school.

C.the number of South African pupils learning Afrikaans has increased

D.many South African pupils use Afrikaans at school instead of at home.小题3: The underlined word “decline” in the last paragraph is closest in meaning to “_________”.

A.going downhill

B.spreading widely

C.growing upwards

D.developing further小题4: What is the survey in the passage mainly about?

A.The use of native languages in South African families.

B.The language choice and use among South African pupils.

C.The progress in South Africa’s language teaching education

D.The spread of English at schools in South Africa.