1.題目翻譯：
①某有機物含有C、H、S元素.質量為1.886g的樣品在氧氣中燃燒,生成CO2,H2O和SO2.
②這些氣體被通入313.3ml濃度為0.0200mol/L的酸性KMnO4溶液,使得SO2被氧化為SO4 2-,同時一部分KMnO4被還原為Mn 2+.
③然后將向31.33ml的剩余溶液樣品（仍含有未被還原的KMnO4）中加入31.33ml濃度為0.0300mol/L的SnCl2溶液,其中的SnCl2為過量,足以將剩余的KMnO4全部還原為Mn 2+.
④反應后用0.0100mol/L的KMnO4溶液滴定測量溶液中剩余的SnCl2,使用0.02242L的該KMnO4溶液恰好達到滴定終點.
根據(jù)上述條件,求被燃燒的有機物樣品中S元素的質量分數(shù).
依次發(fā)生反應：
①CxHySz+(x+0.25y+z)O2→xCO2+(0.5y)H2O+zSO2
②5SO2+2(MnO4 -)+2H2O=2(Mn 2+)+5(SO4 2-)+4(H +)
③2(MnO4 -)+5(Sn 2+)+16(H +)=2(Mn 2+)+5(Sn 4+)+8H2O
④2(MnO4 -)+5(Sn 2+)+16(H +)=2(Mn 2+)+5(Sn 4+)+8H2O
其中③④反應一樣,其中③是在使用SnCl2還原剩余的KMnO4時發(fā)生的,④是在使用KMnO4滴定剩余的SnCl2時發(fā)生的.
由于題干按照實驗順序進行,而且求初始量,因此用逆推法.
最后滴定恰好完成時,使用KMnO4物質的量為0.02242×0.01=0.0002242mol
由反應④可知被滴定的剩余SnCl2物質的量為0.0005605mol
而此前加入的SnCl2總物質的量為0.03×0.03133=0.0009399mol≈0.00094mol
因此在③中反應掉的SnCl2物質的量為0.00094-0.0005605=0.0003794mol≈0.00038mol
由③可知參加反應的KMnO4物質的量為0.00015176mol≈0.000152mol
又因為第③步只取了第②步剩余溶液的10%,因此在第②步過后剩余的KMnO4總物質的量應為0.00015176×10=0.0015176mol≈0.00152mol
又因為最初KMnO4總物質的量為0.3133×0.02=0.006266mol
因此在①中反應掉的KMnO4物質的量為0.006266-0.0015176=0.0047484mol
由反應①可知,被氧化的SO2物質的量為0.011871mol,因此S原子也為0.011871mol,質量為0.379872g
因此S的質量分數(shù)為0.379872/1.886×100%≈20.14%
2.題目翻譯：
焊錫是一種含有錫和鉛的合金.取1.50g的該合金樣品溶于酸中,其中的錫都轉化為+2價氧化態(tài)（即變?yōu)镾n 2+離子）.然后發(fā)現(xiàn),需要0.368g的Na2Cr2O7將Sn 2+全部氧化為Sn4+；在該反應中,Cr元素被還原為Cr 3+離子.要求寫出配平后的在酸性溶液中,Sn 2+與Cr2O7 2-反應的離子方程式.
3(Sn 2+)+(Cr2O7 2-)+14(H +)=3(Sn 4+)+2(Cr 3+)+7H2O
我很困惑如果只要寫一個方程式的話為什么題目中要給出具體數(shù)據(jù)……我原以為它應該是會要答題者求出合金中Sn的質量分數(shù).如果要求這個的話,因為已知Na2Cr2O7的質量為0.368g,可算出其物質的量,再由方程式可求Sn 2+物質的量；由于原合金中的Sn單質全部轉化為離子,因此再求出Sn元素的質量即可.
數(shù)字有一些麻煩,我的思路是沒錯的,但可能會出現(xiàn)一點運算錯誤,建議你可以再檢查一下.BTW,難道這就是傳說中的SAT II的考題么?
兩個題
兩個題
就是氧化還原那塊的~第一個An organic compound contains carbon,hydrogen,and sulfur.A sample of it with a mass of 1.886 g was burned in oxygen to give gaseous CO2,H2O,and SO2.These gases were passed through 313.3 mL of an acidified 0.0200 M KMnO4 solution,which caused the SO2 to be oxidized to SO42-.Only part of the available KMnO4 was reduced to Mn2+.Next,31.33 mL of 0.0300 M SnCl2 was added to 31.33 a mL portion of this solution,which still contained unreduced KMnO4.There was more than enough added SnCl2 to cause all of the remaining MnO4- in the 31.33 mL portion to be reduced to Mn2+.The excess Sn2+ that still remained after the reaction was then titrated with 0.0100 M KMnO4,requiring 0.02242 L of the KMnO4 solution to reach the end point.Based upon all this data,the the percentage of sulfur in the original sample of the organic compound that had been burned is %.
第二個Solder is an alloy containing the metals tin and lead.A particular sample of this alloy weighing 1.50 g was dissolved in acid.All the tin was then converted to the +2 oxidation state.Next,it was found that 0.368 g of Na2Cr2O7 was required to oxidize the Sn2+ to Sn4+ in an acidic solution.In the reaction the chromium was reduced to Cr3+ ion.
Write a balanced net ionic equation for the reaction between Sn2+ and Cr2O72- in an acidic solution.
就是氧化還原那塊的~第一個An organic compound contains carbon,hydrogen,and sulfur.A sample of it with a mass of 1.886 g was burned in oxygen to give gaseous CO2,H2O,and SO2.These gases were passed through 313.3 mL of an acidified 0.0200 M KMnO4 solution,which caused the SO2 to be oxidized to SO42-.Only part of the available KMnO4 was reduced to Mn2+.Next,31.33 mL of 0.0300 M SnCl2 was added to 31.33 a mL portion of this solution,which still contained unreduced KMnO4.There was more than enough added SnCl2 to cause all of the remaining MnO4- in the 31.33 mL portion to be reduced to Mn2+.The excess Sn2+ that still remained after the reaction was then titrated with 0.0100 M KMnO4,requiring 0.02242 L of the KMnO4 solution to reach the end point.Based upon all this data,the the percentage of sulfur in the original sample of the organic compound that had been burned is %.
第二個Solder is an alloy containing the metals tin and lead.A particular sample of this alloy weighing 1.50 g was dissolved in acid.All the tin was then converted to the +2 oxidation state.Next,it was found that 0.368 g of Na2Cr2O7 was required to oxidize the Sn2+ to Sn4+ in an acidic solution.In the reaction the chromium was reduced to Cr3+ ion.
Write a balanced net ionic equation for the reaction between Sn2+ and Cr2O72- in an acidic solution.
英語人氣：435 ℃時間：2020-08-30 10:49:18
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