问题 实验题

K3[Fe(C2O43]·3H2O[三草酸合铁(Ⅲ)酸钾晶体]易溶于水,难溶于乙醇,可作为有机反应的催化剂。实验室可用铁屑为原料制备,相关反应过程如下。请回答下列问题:

(1)铁屑中常含硫元素,因而在制备FeSO4时会产生有毒的H2S气体,该气体可用氢氧化钠溶液吸收。下列吸收装置正确的是               (填序号)。

(2)在得到的FeSO4溶液中需加入少量的H2 SO4酸化,目的是                  ,得到K3[Fe(C2O4)3]溶液后,加入乙醇的目的是                           

(3)晶体中所含结晶水可通过重量分析法测定,主要步骤有:①称量,②置于烘箱中脱结晶水,③冷却,④称量,⑤重复②~④至恒重,⑥计算。

步骤⑤的目的是                                                                 

(4)C2O可被酸性KMnO4溶液氧化为CO2气体,故实验产物中K3[Fe(C2O33]·3H2O含量测定可用KMnO4标准溶液滴定。

①写出滴定过程中发生反应的离子方程式                                            

②下列滴定操作中使滴定结果偏高的是             (填序号)。

A.滴定管用蒸馏水洗涤后,立即装入标准液

B.锥形瓶在装待测液前未用待测液润洗

C.滴定前滴定管尖嘴处有气泡,滴定后气泡消失

D.读取标准液体积时,滴定前仰视读数,滴定后俯视读数③取产物10.0 g配成100 mL溶液,从中取出20 mL于锥形瓶中,用浓度为0.1mol·L-l的酸性KMnO4溶液滴定,达到滴定终点时消耗酸性KMnO4溶液24.00mL,则产物中K3 [Fe(C2O43]·3H2O的质量分数为    [已知摩尔质量M{ K3[Fe(C2O43]·3H2O)="491" g·mol-l]。

答案

(1)A(2)抑制Fe2的水解 三草酸合铁酸钾难溶于乙醇,便于析出;(3)确保结晶水全部失去;

(4)①5C2O42+2MnO4+16H=2Mn2+10CO2↑+8H2O;②AC ③49.1%

题目分析::(1)该装置中硫化氢与氢氧化钠溶液接触面积大,从而使硫化氢吸收较完全,且该装置中气压较稳定,不产生安全问题,故A正确;硫化氢与氢氧化钠接触面积较小,所以吸收不完全,故B错误;没有排气装置,导致该装置内气压增大而产生安全事故,故C错误;该装置中应遵循“长进短出”的原理,故D错误;所以选A;

(2)硫酸亚铁易水解而是其气压呈酸性,加热稀硫酸能抑制亚铁离子水解;双氧水不稳定,温度高时,双氧水易分解,为防止双氧水分解,温度应低些,根据相似相溶原理知,三草酸合铁酸钾在乙醇中溶解度小,所以可以用乙醇使三草酸合铁酸钾析出;

(3)晶体易吸水,为防止吸水步骤③需要在干燥器中进行,步骤⑤的是检验晶体中的结晶水是否已全部失去;

(4)①化合价C:+3→+4,改变量(4-3)×2=2,Mn:+7→+2,改变量(7-2)×1=5,根据化合价升降总数相等,所以在C2O42前配5,MnO4前配2,根据C和Mn原子守恒,分别在CO2和Mn2前配10和2,根据电荷守恒,在H前配16,最后根据离子方程式两边的H个数相等在水前面配8,经检验离子方程式两边的氧原子相等,得到离子方程式为5C2O42+2MnO4+16H=2Mn2+10CO2↑+8H2O;

②A.滴定管没有用标准液润洗,浓度减小,消耗的标准液体积比实际体积变大,测定结果偏高;

B.锥形瓶未润洗,所取待测液的量没变,故不影响V(标准),所以滴定结果无影响

C.由于气泡的体积计入了标准液消耗的体积,使得标准液体积比实际体积增大,测定结果偏高;

D.读取标准液体积时,开始仰视读数,滴定结束时俯视读数,造成V(标准)偏小,测定结果偏低;

故选AC.

③  5K3[Fe(C2O4)3]·3H2O         ~              15C2O42-          ~             6MnO4

5×491g                                               6mol

x                                         24.00mL×10-3×0.1mol·L-l

x =0.982

K3 [Fe(C2O43]·3H2O的质量分数0.982/2×100%=49.1%

选择题
完形填空
完形填空。
     It was the night before the composition was due. As I looked at the list of topics, "The Art of Eating
Spaghetti (意大利面条)" caught my eye. The word "spaghetti" brought back the    1    of an evening at
Uncle Alien's in Belleville    2    all of us were seated around the table and Aunt Pat    3    spaghetti for
supper. Spaghetti was an exotic (外来的) treat in    4    days. Never had I eaten spaghetti, and    5    of
the grown-ups had enough experience to be    6    it. What laughing    7    we had about the    8   
respectable method for moving spaghetti from plate to mouth.    9   , I wanted to write about that, but
I wanted to   10   it down simply for my own   11   not for Mr. Fleagle, my composition teacher.   12  ,
I would write something else.
     When I finished it the night was half gone and there was no   13   left to write a proper composition
for Mr. Fleagle. There was no choice next morning but to   14   my work. Two days passed before Mr.
Fleagle returned the   15   papers. He said, "Now, class, I want to read you a composition," "The Art of
Eating Spaghetti".
     My words! He was reading my words out   16   to the whole class.   17   laughed, then the whole
class was laughing with open-hearted enjoyment. I did my best not to show   18  , but what I was feeling
was pure happiness,   19   my words had the power to make people   20  .

( )1.A.memory      
( )2.A.when         
( )3.A.cooked      
( )4.A.their       
( )5.A.none        
( )6.A.careful about
( )7.A.speeches     
( )8.A.nearly       
( )9.A.Especially  
( )10.A.settle      
( )11.A.work        
( )12.A.However      
( )13.A.time        
( )14.A.give up      
(     )15.A.written      
( )16.A.loud        
(     )17.A.People      
( )18.A.shock        
( )19.A.if          
( )20.A.excited      

B.thought   
B.where     
B.served    
B.past     
B.one       
B.good at   
B.lessons   
B.naturally 
B.Probable  
B.put       
B.story     
B.Therefore     
B.excuse   
B.continue  
B.graded    
B.fast     
B.Nobody   
B.wonder   
B.for       
B.satisfied 
C.knowledge 
C.since    
C.got       
C.last      
C.any      
C.fond of   
C.sayings   
C.officially
C.Suddenly  
C.bite      
C.luck     
C.As for him    
C.way       
C.hand in   
C.collected  
C.slowly   
C.Somebody  
C.worry     
C.while     
C.think     
D.experience       
D.after           
D.made              
D.those              
D.neither         
D.interested in     
D.arguments          
D.socially          
D.fortunately     
D.let                
D.joy           
D.Except for that                  
D.idea              
D.delay             
D.signed             
D.calmly           
D.I               
D.pleasure          
D.although          
D.laugh