问题 选择题

用惰性电极电解一定浓度的硫酸铜溶液,通电一段时间后,向所得的溶液中加入0.1mol Cu2 (OH)2CO3后恰好恢复到电解前的状态(不考虑二氧化碳的溶解)则电解过程中共转移的电子数为(  )

A.0.4mol

B.0.5mol

C.0.6mol

D.0.8mol

答案

电解硫酸铜时,初阶段:2CuSO4+2H2O

 通电 
.
 
2Cu↓+O2↑+2H2SO4,后阶段:2H2O
 通电 
.
 
2H2↑+O2↑,

如果只按照第一阶段的电解,反应只需要加入CuO或CuCO3就可以,但是现在加入的是Cu2(OH)2CO3,相当于多加入了一个水(0.1molH2O),这0.1mol的水,应该是第二阶段的反应进行,该阶段转移了0.4mol电子,第一阶段转移了0.2mol电子,所以总共转移电子0.6mol.

故选C.

选择题
阅读理解

The need to feed a growing population is putting much pressure on the world's supply of water. With 97% of the world's water too salty to be drunk or used in agriculture, the worldwide supply of water needs careful management, especially in agriculture. Although the idea of a water shortage(短缺)seems strange to someone fortunate enough to live in a high rainfall country, many of the world's agricultural industries experience constant water shortages.

Although dams can be built to store water for agricultural use in dry areas and dry seasons, the costs of water redistribution(重新分配)are very high. Not only is there the cost of the engineering itself, but there is also an environmental cost to be considered. Where valleys(山谷)are flooded to create dams, houses are lost and wildlife homes destroyed. Besides, water may flow easily through pipes to fields, but it cannot be transported from one side of the world to the other. Each country must therefore rely on the management of its own water to supply its farming requirements.

This is particularly troubling for countries with agricultural industries in areas dependent on irrigation (灌溉). In Texas, farmers' overuse of irrigation water has resulted in a 25% reduction of the water stores. In the Central Valley area of southwestern USA, a huge water engineering project provided water for farming in dry valleys, but much of the water use has been poorly managed.

Saudi Arabia's attempts to grow wheat in desert areas have seen the pumping of huge quantities of irrigation water from underground reserves. Because there is no rainfall in these areas, such reserves can only decrease, and it is believed that fifty years of pumping will see them run dry.

小题1:What is most likely to be discussed in the paragraph that follows?

A.Ways to reduce the costs of building dams.

B.Steps to improving water use management.

C.Measures to deal with worldwide water shortages.

D.Approaches to handling the pressure on water supply.小题2:From the first two paragraphs we learn that________.

A.much of the world's water is available for use

B.people in high rainfall countries feel lucky

C.the costs of water redistribution should be considered

D.water can be easily carried through pipes across the world小题3:The text is mainly about________.

A.water supply and increasing population

B.water shortages and environmental protection

C.water redistribution and wildlife protection

D.water use management and agriculture