题干

下列说法正确的是(     )

A:欲分离硝酸钾和氯化钠的混合物(物质的量比为1:1),先将样品溶解,然后加热至表面出现晶膜后再冷却,过滤得硝酸钾晶体;再将母液加热至大量晶体析出后,用余热蒸干,得氯化钠晶体

B:摘下几根火柴头,浸于水中,片刻后取少量溶液于试管中,加AgNO3溶液、稀硝酸,若出现白色沉淀,就说明含有氯元素

C:实验室制取肥皂:将适量植物油、乙醇和NaOH溶液混合,并不断搅拌、加热,直到混合物变稠,即可得到肥皂

D:阿司匹林制备实验中,在粗产品中加入饱和NaHCO3溶液处理除去水杨酸聚合物

上一题 下一题 0.0难度 选择题 更新时间:2019-04-19 09:37:38

答案(点此获取答案解析)

D

同类题1

     A serious earthquake can be a terrible experience, and it is easy to forget safety measures(措施) in disorder(混乱). Fortunately, most earthquake safety measures are common sense, but if you forget everything else, re­member the following instructions: drop, cover, and hold on. Also, most of earthquake deaths hap­pen after the earthquake, so remember that the danger does not end when the shaking does!

     If you stay indoors during an earthquake, move away from unsupported areas and windows. Try to get under a doorway or another area of the building which is held up by strong beams(梁).  Stay under a table or desk only if it is very strong. Do not rush to lifts, because it is far safer to stay where you are. Cover your head with your arms around it and curl (蜷缩) into a ball, and wait for the shaking to stop.

     If you stay outdoors during an earthquake, move to an area which is as open as possible. Don't move to build­ings, electric poles and other objects which may fall during an earthquake and injure you. Protect your head and stay low to the ground till the shaking ends and it is safe to move.

     After an earthquake, many buildings are less strong, although they appear safe. If you stay indoors, move people from the building quickly and help disabled or injured people. Once outdoors, move well away from the building so that if it falls down, you will not be injured. Wait till public safety officials an­nounce that it is safe to stay indoors.

     By planning ahead and keeping calm during an earthquake, you can greatly increase your chances of survival(生存) without injury.