英语周报2021~2020第21期答案

19.(10分)(1)平衡压强(1分)(直形)冷凝管(1分)2)①C(2分)②不受影响(2分)(3)0057(v1av2×100%(2分)(4)寻找最佳实验条件(2分)【解析】(1)a管的作用是平衡压强仪器d的名称是(直形)冷凝管(2)①此实验是利用高氯酸(高沸点酸)将样品中的氟元素转化为HF(低沸点酸)蒸出。硝酸和盐酸易挥发,A、B项错误;硫酸沸点高,难挥发,C项正确。②SF;水解生成HF,若有SiF,生成对实验结果无影响(3)氟化稀土样品中氟的质量分数=ov=eV2)×10-mo×3×19g·mo×100%9.057y=V)×100%,(4)该操作的目的是通过做对比实验,寻找最佳实验条件

reading, with a confused look on her face. Dannis stoodup,glared at her and shouted, "You stole my wallet! "Thecrowds began to gossip. The girl turned deadly pale, loo-king so restless that words failed her. A strange silencehung in the air. Abruptly, she leaped from the seatParagraph 2The gird ran and Dannis ran after her. After a whileDannis finally grabbed her by the arm. At exactly thatmoment,a policeman approached them and asked aboutwhat happened. Dannis hastened to explain it while the girlfrowned with a shake of her head. After further enquiriesthe policeman took out a wallet and handed it to Dannisadding that someone had found it in the toilet. What a mis-take he had made! Overwhelmed by guilt, Dannis made anapology to the girl第三节One possible versionParagraph 1A seat beside her was empty, and Dannis occupied itHe felt a wave of anger swept over him, "Where is my wal-let? he yelled. The black-haired girl glanced up from her

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