题干

某同学采用工业大理石(含有少量SiO2、Al2O3、Fe2O3等杂质)制取CaCl2•6H2O,设计了如下流程:

下列说法不正确的是(   )

A:固体Ⅰ中含有SiO2,固体Ⅱ中含有Fe(OH)3

B:使用石灰水时,要控制pH,防止固体Ⅱ中Al(OH)3转化为AlO2

C:试剂a选用盐酸,从溶液Ⅲ得到CaCl2•6H2O产品的过程中,须控制条件防止其分解

D:若改变实验方案,在溶液Ⅰ中直接加氨水至沉淀完全,滤去沉淀,其溶液经蒸发浓缩、冷却结晶也可得到纯净CaCl2•6H2O

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答案(点此获取答案解析)

D

同类题1

阅读理解

    Time flies, or so they say. No matter where you are, humans are constantly measuring and checking time. Some of us are good at it—planning and doing things ahead of time—while others are always trying to beat the clock and do things at last. What about if you are behind time?

    Delay can be serious. If you were one minute late for work, would you resign? It may sound extreme to many of us, but that is exactly what occurred in the UK upper chamber of parliament, the House of Lords, in January 2018. International development minister Lord Bates arrived one minute late, and, as a result, was unable to answer a scheduled question. Instead of trying to make up for lost time, he resigned on the spot. He apologised for his discourtesy and stated that he was ashamed. His resignation, though, was not accepted by the UK prime minister.

    So, how late is too late? Many cultures take punctuality very seriously, whereas others seem to accept lagging behind as just the normal way of things. BBC employees from Latin America, Rwanda and Sri Lanka said that there are more flexible attitudes to timekeeping in their cultures. In Latin America, things may happen five minutes, 20 minutes, an hour or even two after they were planned. Whereas, in Sri Lanka, lateness is a part of the daily routine. This is because of poor infrastructure and heavy traffic conditions. In Rwanda, those who attend to deadlines with strick timekeeping are said to be “like a typical European”.

    On the other hand, German and Japanese employees mentioned a stricter adherence to time. In Japan, it is common to make an effort to arrive with time to spare for an appointment. Those who arrived at the stroke of nine to a meeting starting at 9 am would be considered late. In Germany, however, if a dinner party were to begin at eight, a person who had arrived five minutes prior, may walk around the block to make sure that they arrive at eight on the dot.

同类题4

阅读理解

    It was dangerously cold. A few drivers slipping and sliding off the road and back on again had cut deep ruts(车辙)in the mud. And the ruts became frozen solid. The drum of our truck's aging engine worried us.

    Trees and bushes heavy with snow bent to form an icy tunnel. We inched along the scary route as Howard grasped the steering wheel(方向盘)tightly, trying to keep the truck in the ruts. We were now riding through a nightmare with no going back. I kept praying the truck would not quit.

    However, the engine's coughing grew worse. We came to a bumping stop. Hot tears ran down my face. We noticed a small house off in the distance. “I will go for help.” Howard's words ruined my common sense and panic took over. We would take the children — we would walk to that house together!

    But the snow was deep, and our two children, asleep in the cab, were too heavy to carry. My husband convinced me to let him go alone. If no one was home or they didn't answer the door, he would come back and we'd try to hike out to a main road. For now, it was safer in the truck. I wish I could say I have faith, but when he walked away, I was mad at the world.

    It seemed as if hours had passed before I heard a familiar voice and a kind laugh of another man as they approached in the snow. The older fellow invited us to go up to the house where his wife was waiting. Two wide-awake kids moved across the seat, ready for adventure. Their voices and laughter carried in the cold night air. When we finally got close, a cheerful woman opened the door. Warm air and the smell of hot buttered popcorn and chocolate drew us in.

     Relieved, my prayers were heard!