问题 问答题

以碳酸钙、碳酸钠、水为原料制取氢氧化钠,可设计如下反应过程:

碳酸钙

高温
氧化钙
氢氧化钙
碳酸钠
氢氧化钠.

写出上述反应涉及的化学方程式,并注明反应类型.

答案

石灰石在高温下煅烧生成氧化钙和二氧化碳,反应的化学方程式为:CaCO3

 高温 
.
 
CaO+CO2↑;该反应符合“一变多”的特征,属于分解反应.

氧化钙与水反应生成氢氧化钙,反应的化学方程式为:CaO+H2O═Ca(OH)2;该反应符合“多变一”的特征,属于化合反应.

氢氧化钙与碳酸钠溶液反应生成碳酸钙沉淀和氢氧化钠,反应的化学方程式为:Ca(OH)2+Na2CO3═CaCO3↓+2NaOH;该反应是两种化合物相互交换成分生成两种新的化合物的反应.

故答案为;CaCO3

 高温 
.
 
CaO+CO2↑;分解反应;CaO+H2O═Ca(OH)2;化合反应;Ca(OH)2+Na2CO3═CaCO3↓+2NaOH;复分解反应.

阅读理解

Compassion is a desire within us to help others. With effort, we can translate compassion into actions. An experience last weekend showed me this is true. I work part-time in a supermarket across from a building for the elderly. These old people are out main customers, and it’s not hard to lose patience over their slowness. But last Sunday, one aged gentleman appeared to teach me a valuable lesson. This untidy man walked up to my register(收款机)with a box of biscuits. He said he was out of cash (现金), had just moved into his room, and had nothing in his cupboards. He asked if we could let him have the food on trust. He promised to repay me the next day.

I couldn’t help staring at him. I wondered what kind of person he had been ten or twenty years before, and what he would be like if luck had gone his way. I had a hurt in my heart for this kind of human soul, all alone in the world. I told him that I was sorry, but store rules didn’t allow me to do so. I felt stupid and unkind saying this, but I valued my job.

Just then, another man, standing behind the first, spoke up. If anything, he looked more pitiable. “Change it to me,” was all he said.

What I had been feeling was pity. Pity is soft and safe and easy. Compassion, on the other hand, is caring in action. I thanked the second man but told him that was not allowed either. Then I reached into my pocket and paid for the biscuits myself. I reached into my pocket because these two men had reached into my heart and taught me compassion.

41. The aged gentleman who wanted to buy the biscuits_________.

A.promised to obey the store rules    

B.forgot to take any money with him

C.hoped to have the food first and pay later   

D.could not afford anything more expensive

42. Which of the following best describes the old gentleman?

A.kind and lucky        B.poor and lonely

C.friendly and helpful D.hurt and disappointed

43. The writer acted upon the store rules because_________.

A.he wanted to keep his present job  

B.he felt no pity for the old gentleman

C.he considered the old man dishonest     

D.he expected someone else to pay for the old man

44. What does the writer learn from his experience?

A.Wealth is more important than anything else    

B.Helping others is easier said than done

C.Experience is better gained through practice

D.Obeying the rules means more than compassion.

单项选择题