问题 填空题

随着材料科学的发展,金属钒及其化合物得到了越来越广泛的应用,并被誉为“合金维生素”。已知钒的原子序数为23,回答下列问题:

(1)钒被认为是一种稀土元素,广泛分散于各种矿物中。钾钒铀矿中的钒原子最外层已达8电子稳定结构,其化学式为K2H6U2V2O15,若用氧化物的形式表示,该化合物的化学式为_______________________。

(2)测定钒含量的方法是先把钒转化成V2O5,V2O5在酸性溶液里转变成VO2+,再用盐酸、硫酸亚铁、草酸等测定钒。总反应式可表示为:

VO2++H2C2O4→VO++CO2+H2O(未配平)

其中还原剂是_______。若消耗0.9 g草酸,所对应钒元素质量是_______g。

答案

⑴K2O·2UO3·V2O5·3H2O。 ⑵H2C2O4      0.51。  

(1)要用氧化物形式表示该化合物的化学式,必须先确定钒、铀的化合价。由于钾元素必定显+1价,根据“钒原子最外层已达8电子稳定结构”,可推出钒应失去5个电子变成氩原子结构,所以钒元素显+5价。再根据化合价规律可计算出铀的化合价应是+6。

(2)将题给反应式配平可得:VO2++H2C2O4= VO++2CO2↑+H2O。根据配平后的方程式计算可得到钒元素的质量数值。

阅读理解

阅读理解。

     Joe and Helen Mills had two little children. One was six and the other four. They

always resisted going to bed, and Helen was always complaining (抱怨) about this and asking Joe for help.  But as he did not come home until after they had gone to bed

during the week, he was unable to help except at weekends.

    Joe considered himself a good singer, but really his voice was not at all musical.

However, he decided that, if he sang to the children when they went to bed, it would

help them to relax, and they would soon go to sleep,

     He did this every Saturday and Sunday night until he heard his small son

whispered to his younger sister, "If you pretend that you're asleep, he stops. "  

1. The children always resisted going to bed, which          .

A. made Joe suffer a lot

B. satisfied their mother

C. Helen was not satisfied with

D. gave Helen much happiness

2.  The husband couldn't help the wife to look after the children          .      

A. because he returned from work too late every day

B. since his voice sounded like a singer's

C. except on Saturday and Sunday

D. for he did not come home until after the children had gone to bed at weekends

3. Joe worked         .

A. all the week including Saturday and Sunday

B. during the week including the weekends

C. every day but Saturday and Sunday

D. every week except on Sunday     

4. Which of the following conclusions can we draw from the above story?

A. Joe's song did help the children to relax.

B. With Joe's help, the children went to sleep.

C. The wife must be thankful to her husband for the great help.

D. The children were so tired of their father's voice that they pretended to be asleep.

5. This joke tells about          .

A. Joe and Helen

B. Helen's trouble

C. Joe's foolery

D. the bright idea of the two small children

选择题