问题 填空题

测定水中的碱度(只采用含OH、CO32-和HCO3碱性离子的水样)是用中和滴定法,即用标准溶液进行滴定,此时各种碱度与酸的反应为:()-------------------------------------①()-----------------------------------②()------------------------------③如果水的pH较大,用酸滴定时,上述三个反应式将依次进行。当用甲基橙作指示剂时,因终点的pH为4.2,上述三个反应都可以进行到底。可测得水的全碱度,又称甲基橙碱度;如果用酚酞作指示剂,因终点的pH为8.3,反应只有①和②式可以进行,而反应③并不进行,此时测得水的酚酞碱度。

答案

参考答案:OH+H+—→H2O;CO32-+H+—→HCO3;HCO3+H+—→CO32-+H2O

阅读理解

Two children stood outside the door with old coats. “Any old papers, Lady?” asked one of them.

I was busy. I wanted to say no, but I saw that their shoes were broken and wet. “Come in and I’ll make you a cup of hot tea.” They came in, saying nothing. Their shoes left snow on the floor.

I gave them tea and bread to protect them against the cold outside. Then I went back to the kitchen and started my housework again.

The silence in the front room surprised me. I looked in.

The girl held the empty cup in her hands, looking at it. The boy asked me in a low voice, “Lady, are you rich?”

Am I rich? Oh, no! I looked at my old things in my room.

The girl put her cup back in its saucer(茶碟) carefully. “Your cups match your saucers.”

They left then, holding their papers against the wind. They hadn’t said thank you. They didn’t need to. They had done more than that. The blue cups and saucers were simple. But they said that they matched. The potatoes and meat before me, a roof over our hands, my husband with a job—these things matched, too.

I moved the chairs back from the fire and cleaned the living room. The prints of their small shoes were still wet on my floor. I let them be. I wanted them there to remind me how rich I was.

小题1:The writer let the two children in _________.

A.to offer them some warm clothes

B.to serve them tea and food

C.to sell them some old papers

D.to show them how rich she was.小题2:We can learn from the passage that_______.

A.the writer was in fact not very rich

B.the children took away many old papers

C.the writer’s husband was out of work

D.the two children were looking for a job小题3: It can be inferred(推断) from the passage that _______.

A.it was snowing outside when the story happened

B.the two children thanked the writer and then left

C.the two children were not polite to the writer

D.the writer had a set of new furniture in her house小题4:The underlined sentence “I let them be” means  “_________”.

A.I dislike them

B.I didn’t want to see them

C.I cleaned them

D.I left them there小题5: What’s the best title of the passage?

A.Any Old Papers?

B.Matching Cups and Saucers

C.Are You Rich?

D.Two Poor Children

单项选择题