题干

CuSO4溶液与Na2CO3溶液混合时产生蓝绿色沉淀,某实验小组进行实验,探究蓝绿色沉淀的组成。

【查阅资料】

i.氢氧化铜是一种蓝色絮状沉淀,难溶于水,溶于酸、氨水等,受热会分解。

ii.碳酸铜是蓝绿色粉末状固体,受热易分解,遇水转化为氢氧化铜和碱式碳酸铜的混合物。

iii.碱式碳酸铜呈孔雀绿颜色,又叫孔雀石,难溶于水,溶于酸、氨水等,在空气中加热会分解。

【提出假设】

假设1:沉淀为Cu(OH)2

假设2:沉淀为CuCO3

假设3:沉淀为碱式碳酸铜[化学式可表示为xCuCO3•yCu(OH)2]

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    One autumn morning, I spotted a pair of wild geese on our pond. The beautiful sight caught me by 1 because I'd never seen geese there before. Thinking they would soon leave, I 2 the chance to get close to them. I wondered where they came from and why they had chosen our pond.

    The next morning, the geese were still my 3 I walked round to the mailbox, showing them I meant no harm4I couldn't resist getting a 5 look. I hid behind some trees and 6 the handsome pair quietly through the branches. I was surprised to see they were staring at me, too!

    As days passed, I started 7 to them on my trips to the mailbox. They craned (伸长) their necks and raised their heads 8 but seemed to realize I was their friend. By then, my curiosity about 9 they were staying so long at the pond changed to10. As they were feeding in the grass the other day, I discovered the reason for their 11the male had a broken left wing. He couldn't 12 and his faithful mate wouldn't leave him behind. I asked a biologist what to do. He explained that sometimes a13 wing will heal by itself and suggested letting nature take its course.

    On the first day of November, I was working in the neighborhood of the geese with my tractor. As I bent to fasten a chain from the tractor, I 14some movement from the corner of my eye. Both geese were running towards the pond. Their wings were 15 like crazy, struggling for take off. Gradually, they flew over the pond. They16 enough altitude to fly past a neighbor's house, and then circled back towards me, flying no more than 50 feet over my head as if to say goodbye. Then they were out of my17.

    The season's first snowflakes fell the very next day. The birds must have 18 that winter was coming, and it was time to go. I became fond of them during their 19 visit to our pond, and now I miss them. I'll never forget their 20 to each other.