问题 实验题

.(12分)某铝合金(硬铝)中含有镁、铜、硅,为了测定该合金中铝的含量,某同学设计如下试验:

(1)取样品 ag ,称取时使用的仪器名称为          

(2)将样品溶于足量的稀盐酸中,过滤,滤渣中含有        ,在溶解过滤时使用的玻璃仪

器有         

(3)往滤液中加入过量的NaOH溶液、过滤,写出该步操作中有关的离子方程式                        

(4)在第( 3 )步的滤液中通入足量CO2,过滤。有关反应的离子方程式是                                 

(5)步骤(4)过滤后的滤渣用蒸馏水洗涤数次后,烘干并灼烧至质量不再减轻为止,冷却后称量,质量为bg,则原样品中铝的质量分数是                   

(6)若步骤(3)中加入氢氧化钠的量不足,则实验结果偏      (填“高”、“低”或“不影响”,下同);若步骤(5)中滤渣没有洗涤,则实验结果偏      ;若滤渣燃烧不充分,则实验结果偏         

答案

(1)托盘天平     (2)硅、铜;烧杯、漏斗、玻璃棒

(3) Al3+ + 4OH = [Al(OH)4]、Mg2+ + 2OH = Mg(OH)2

(4) [Al(OH)4]+ CO2 = Al(OH)3↓+ HCO3 (5) 9b/17a      (6) 低 ;高 ;高

(1)称量固体药品使用托盘天平。

(2)铜、硅和盐酸不反应,所以滤渣是铜和硅。溶解过滤时使用的玻璃仪器有烧杯、漏斗、玻璃棒。

(3)加入强酸生成氢氧化镁和氢氧化铝沉淀,但氢氧化铝是两性氢氧化物,能溶于强碱中。有关的方程式为Al3+ + 4OH = [Al(OH)4]、Mg2+ + 2OH = Mg(OH)2↓。

(4)滤液中含有偏铝酸盐,通入CO2生成氢氧化铝沉淀,方程式为[Al(OH)4]+ CO2 = Al(OH)3↓+ HCO3

(5)沉淀是氢氧化铝,灼烧得到氧化铝,所以铝放热质量分数为=9b/17a。

(6)若步骤(3)中加入氢氧化钠的量不足,则滤液中偏铝酸盐的量就偏低,最后结果偏低。若步骤(5)中滤渣没有洗涤,则实验结果偏,则氢氧化铝的质量偏大,结果偏高。若滤渣燃烧不充分,则氧化铝就偏高,结果偏高。

完形填空
完型填空。
     Throughout history man has had to accept the fact that all living things must die. But people now live
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they form do not function as well as they    5  in childhood and teenage years. The body provides less    6  against disease and is more   7  to have an accident.
     A number of related causes may   8   to aging. Some cells of the body have a fairly long life, but they
are not   9   when they die. As a person ages,    10  of brain cells and muscle cells decreases.   11   body
cells die and are replaced by new cells. In an aging person the   12   cells may not be as workable or as
capable   13   growth as those of a young person.
     Another   14   in aging may be changes within the cells    15  . Some of the protein chemicals in cells are known   16   with age and become less elastic (有弹性). This is why the skin of old people wrinkles and
  17  . This is also the reason why old people   18   in height. There may be other more important chemical changes in the cells. Some complex cell chemicals, such as DNA and RNA, store and   19   information
that the cells need. Aging may affect this   20   and change the informationcarrying molecules so that they
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