做乙醛被Cu（OH）2氧化实验时，有以下步骤：①加入0.5mL乙醛溶液；②加入2%硫酸铜溶液4-5滴；③加入10%NaOH溶液2mL；④加热至沸腾．其正确的操作顺序是（ ）
A．①②③④
B．③②①④
C．②③①④
D．①③②④
乙醛和新制的Cu（OH）2反应：CH3CHO+2Cu（OH）2
CH3COOH+Cu2O+2H2O；该反应的本质是：乙醛中的醛基具有还原性，新制的氢氧化铜具有氧化性，醛基与氢氧化铜中的+2价的铜发生氧化还原反应．做该实验先配制氢氧化铜悬浊液，然后加乙醛，加热
实验的步骤：因碱需过量所以第一步加入10%NaOH溶液2mL选③；然后加入2%硫酸铜溶液4-5滴，配制氢氧化铜选②；加入0.5mL乙醛溶液选①；加热至沸腾选④，
所以该实验中操作步骤的排列正确顺序为：③②①④，
故选：B．
Stop! Listen! What do you hear? You may hear many different sounds. Some of those sounds may be noisy. Noise is loud and unwanted sound. Noise can be caused by many kinds of machines, such as motorcycles, jet planes, tractors and so on. And, to some people, rock bands are also noise. What happened to people who live near noisy machines or use them over a period of time? Doctors find that these people have trouble in sleeping, But, most important, constant loud noise can cause a loss of hearing. Scientists use a unit of measure called a decibel to measure the loudness of a sound. The sound of a quiet room, for example, measures 35 decibels. Talking measures between 40 and 65 decibels. Sounds from traffic and from some rock bands can measure over 120 decibels. Noise at this high level causes the greatest hearing loss. 小题1: From the article we know noise is ___________. wanted sound B. loud and unwanted sound C. all sounds that you can hear D. comfortable sound 小题2: A “decibel” is a _________
help people sleep better B. stop machine C. cause a loss of hearing D. kill people 小题4:The main idea of this passage is that __________ noise pollution can be a serious problem rock bands are noisy noise can cause people to be mad some people hate noise deeply 小题5: Study the chart below, Which room would be the quietest?
C. Room C D. Room D |