2018到2023英语周报八年级外研版第3期答案

2018到2023英语周报八年级外研版第3期答案已经整理完毕，供同学们学习参考，更多英语周报答案，请关注本站。

18.(1)排尽装置内的空气,防止装置A产生的NO被氧化(2分)(2)铜丝溶解变细,溶液变蓝色,有无色气体产生(2分)(3)碱石灰或生石灰(1分)(球形)干燥管(1分)防止装置E中的水蒸气进入装置C中与Na2O2反应(4)2NO+ Na, O,-2NaNO,(1 zr)(5)3MnO7+4H++5NO-3Mn2++5NO+2H2O(2分)(6)取少量待测固体分别于两支试管中,向其中分别滴加硝酸酸化的硝酸银溶液,有白色沉淀出现的为氯化钠,没有白色沉淀的是亚硝酸钠(2分)【解析】(1)实验开始时,向装置中通入一段时间氮气的目的是排尽装置内的空气,防止装置A产生的NO被氧化。(2)铜丝与稀硝酸反应的实验现象为铜丝溶解变细,溶液变蓝色,有无色气体产生。(3)通入的氮气会把装置A中的水蒸气带入装置C中与Na2O2发生反应,故装置B的作用是干燥气体,可选碱石灰或生石灰。盛装碱石灰的玻璃仪器为球形干燥管,装置D的作用是防止装置E中的水蒸气进入装置C中与Na2O2发生反应。(4)装置C中发生反应的化学方程式为2NO+Na2O22NaNO2(5)装置E中发生反应的离子方程式为3MnO4+4H++5NO=3Mn2++5NO3+2H2O(6)氯化银为难溶物,不溶于硝酸;亚硝酸银为难溶物,易溶于硝酸。用硝酸酸化的硝酸银即可鉴别亚硝酸钠与氯化钠。

第二节书面表达(满分25分)with the intention of caring for the old, my classmates and I decided to visit the nursing home last week. Themoment we got there, we began to clean rooms and washed clothes for the old. After that some of us swept thefloor, which made them both happy and excited. Just two hours later, the whole yard was spotlessAs far as I am concerned, this experience is meaningful. For one thing, we helped them do something theycouldn't do on their own. For another, tidy and comfortable environment was also created for them, making themfull of delight. It was through this labor that I fully realized that the awareness of respecting the old should be

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