问题 选择题

下列离子方程式书写正确是

A.向碳酸氢钙溶液中加入过量的氢氧化钠溶液:Ca2++HCO3+OH=CaCO3+H2O

B.将少量氯化铁溶液滴入硫化钠溶液中:2Fe3+S2=2Fe2+S↓

C.次氯酸钙溶液中通入过量二氧化碳:Ca2+2ClO+H2O+CO2=CaCO3↓+2HClO

D.氯化亚铁溶液中加入稀硝酸:9Fe2+4H+NO3=9Fe3+2H2O+NO↑

答案

答案:D

题目分析:判断离子方程式正确与否的方法一般是:(1)检查反应能否发生。(2)检查反应物、生成物是否正确。(3)检查各物质拆分是否正确。(4)检查是否符合守恒关系(如:质量守恒和电荷守恒等)。(5)检查是否符合原化学方程式。A、向碳酸氢钙溶液中加入过量的氢氧化钠溶液生成碳酸钙、碳酸钠和水,因此反应的离子方程式为Ca2++2HCO3+2OH=CaCO3+H2O+CO32,A不正确;B、将少量氯化铁溶液滴入硫化钠溶液中生成单质S、FeS沉淀,离子方程式为2Fe3+2S2=FeS+S↓+Fe2,B不正确;C、次氯酸钙溶液中通入过量二氧化碳生成碳酸氢钙、次氯酸,反应的离子方程式为ClO+H2O+CO2=HCO3↓+HClO,C不正确;D、氯化亚铁溶液中加入稀硝酸发生氧化还原反应,反应的离子方程式为9Fe2+4H+NO3=9Fe3+2H2O+NO↑,D正确,答案选D。

单项选择题

The average person learns most of the 30000~40000 words whose meanings he or she recognizes by hearing them or getting familiar with them in the context or simply absorbing them without conscious effort. The best way to build a good vocabulary, therefore, is to read a great deal and to participate in a lot of good talks. There are relatively few words that we learn permanently by purposefully referring to dictionaries or keeping word lists. However, even those extra few are of value, and no one will make a mistake by working on developing a larger vocabulary. Here are some suggestions of how to do it.

Read plenty of good books. When you come across a new word, or a new meaning of an old word, stop and see if you can understand it from its context. If you can’t, and if you can manage without interrupting the thought of the book too much, look it up in a dictionary or ask somebody and then repeat its meaning to yourself a couple of times. If you are really conscientious, write the word and its meaning in a personal vocabulary list—preferably using it in a sentence, or you can keep a special vocabulary notebook. Go over the list from time to time. Further, try to use a new word in writing or conversation a few times over the next several days.

Listen to good talks and be alert to new words you hear or to new meanings of words you already know. Then treat them just as you treat the new words you read.

Learn and be alert to the parts of words: prefixes, suffixes and roots. Knowing them enables you to make intelligent guesses about the meaning of words.

If you are studying a foreign language, be alert to words in that language which relate to words in English. English has inherited or borrowed much of its vocabulary of 500000~600000 words from Latin, Greek, French, Spanish and German.

In the fourth paragraph, the word“them”refers to()

A. the parts of words

B. prefixes

C. suffixes

D. roots

填空题