Qualitative Analysis of Anions
Written by Denise Tram
In this lab, we are to analyze the different processes that will be used in laboratory to help us gain experience in identifying different anions and how we can become familiar with different anions by observations of the reactions and products. In this lab we separated precipitates and by doing this we were able to confirm the reactions that create a precipitate and we used this to identify which anions can be reacted in which a gas formation and a color change appears. By being able to correctly proceed in this lab, we will be able to use this information in future experiments in which the solutions would be unknown.
1) Begin this section by summarizing your results from the screening tests. Do his by creating table modeled after the one below.
|
Anion |
Test II (18 M H2SO4) |
Test III (AgNO3) |
Test IV (BaCl2/CaCl2) |
Test V (K2MO4) |
|
Cl– |
White bubbling. Blue litmus turned red immediately. White fogging on watch glass. @ 10 min. a little yellow powder left. |
Blue litmus turned red. White Cloudy PPT. formed immediately. |
Blue litmus stayed blue. Cloudy white PPT. turned yellow. |
Transparent pink soln.; after three mins and stirring soln turned bright clear pink. |
|
Br– |
Blue litmus turned red immediately from gas that formed. Bubbling white and @ 10 min. dark orange left over. |
Blue litmus turned red. Cloudy light green-yellow PPT formed immediately |
Blue litmus stayed blue. A little white cloudy ppt. |
Purple on top, yellow clear solution on bottom. At 3 mins. Top turned brown. Stirring made soln light brown color. |
|
I– |
Blue litmus paper turned red. Burning orange brown reaction. Turned silver/gray on top and burnt on the bottom. Fogging on watch glass. @ 10 min orange-yellow and gray left over. |
Blue litmus paper turned red. Cloudy intense green like mucus PPT. formed |
Blue litmus stayed blue. Cloudy white PPT. formed. |
Dark purple ppt form on top. Yellow soln under it. @ 5 min, soln turned brown on top and clear yellow in color. Stirring creates light brown orange color. |
|
SO42- |
No gas and no reaction occurred. Very light blue |
Blue litmus turns red. Silver nitrate added and soln turns light clear blue mist ppt. Ammonia added makes blue ppt on bottom and @ 5 mins. Ppt turns white. |
Ammonia added has no real rxn and soln is clear. Intense white cloudy(milky) ppt formed instantly that settled on bottom. Basic. |
3M sulfuric acid has no rxn and is acidic. Adding potassium makes clear bright purple and acidic. |
|
C2O42- |
No gas formation and no reaction occurred. |
Blue to Red litmus paper. Silver nitrate added makes white cloudy PPT. form. Ammonia added and @ 5 min. ppt. turns clear. |
Ammonia added no rxn. White cloudy PPT formed when barium chlorine and calcium chlorine added. Basic. |
3M sulfuric acid has no rxn and is acidic. Potassium makes clear bright clear color and makes acidic. |
|
CO32- |
Bubbling gas immediately and gas formed turns blue litmus red. |
Red to Blue litmus. Bubbles formed but @ 2 min. stopped. Silver nitrate added white cloudy ppt. appeared on top and yellow mucus color. Ammonia added ppt disappears. |
Ammonia added is clear. Barium added creates jellylike ppt, light white ppt and calcium added white jelly form and translucent. |
3M sulfuric acid makes bubbling and fizzing immediate but stops @ 3mins. Potassium added makes clear bright purple basic. |
|
NO3– |
No gas formed so no reaction. @ 5 min. blue litmus turned red. |
No reaction. |
Working soln: Acidic. Ammonia added makes basic. Barium added and white cloudy ppt formed instantly. Calcium added and no rxn. |
3 M sulfuric acid has no rxn but is acidic. Potassium added creates clear bright purple and red litmus turns to blue so it turned basic. |
2) For each screening test, write a balanced chemical equation for the reaction of each of the seven anions. If an anion does not react for a specific screening test, state “no reaction” for the anion/screening test combination. The equations may be written as net ionic equations or as complete equations. [The background of the experiment uses net ionic equations.]
Screening Test II: Reaction with 18M H2SO4
| Anion | Equations |
| Cl– | Cl–(aq) + H+(aq)à HCl(g) |
| Br– | Br–(aq) + H+ (aq)à HBr(g) |
| I– | I– (aq)+ H+(aq)à HI(g) |
| SO42- | SO42-+ H2SO4 à No Reaction. |
| C2O42- | C2O42-+ H2SO4 à No Reaction. |
| CO32- | CO32-+ H2SO4 àNo Reaction. |
| NO3– | NO3– (aq)+ H+(aq)à HNO3(aq) |
Screening Test III: Reaction with AgNO3
| Anion | Equations |
| Cl– | Cl–(aq) + Ag+(aq)à AgCl(s) |
| Did not dissolve in NH3 | |
| Br– | Br–(aq) + Ag+(aq)à AgBr(s) |
| Did not dissolve in NH3 | |
| I– | I–(aq) + Ag+ (aq)à AgI(s) |
| AgI(s) + 2NH3(aq) àAg(NH3)2+(aq) +I–(aq) | |
| SO42- | No Reaction. |
| C2O42- | No Reaction. |
| CO32- | No Reaction. |
| NO3– | No Reaction. |
Screening Test IV: Reaction with BaCl2 and CaCl2
| Anion | Equations |
| Cl– | BaCl2 à No Reaction. |
| CaCl2à No Reaction. | |
| Br– | BaCl2 à No Reaction. |
| CaCl2à No Reaction. | |
| I– | BaCl2 à No Reaction. |
| CaCl2à No Reaction. | |
| SO42- | SO42- (aq) + Ba2+(aq) àBaSO4 (s) |
| SO42- (aq) + Ca2+(aq) àCaSO4(s) | |
| C2O42- | C2O42- (aq) + Ba2+(aq) àBaC2O4(s) |
| C2O42- (aq) + Ca2+(aq) àCaC2O4 (s) | |
| CO32- | CO32- (aq) + Ba2+(aq) àBaCO3(s) |
| CO32- (aq) + Ca2+(aq) àCaCO3(s) | |
| NO3– | BaCl2 à No Reaction. |
| CaCl2à No Reaction. |
Screening Test V: Reaction with Permanganate
| Anion | Equations |
| Cl– | No Reaction. |
| Br– | 2Br–(aq) + 2H+ (aq) + MnO4–(aq)àBr2(aq)+Mn2+(aq)+H2O(l) |
| I– | I–(aq) +2MnO4– (aq) + H2O(l)àIO3–(aq)+2MnO2(aq)+2OH–(aq) |
| SO42- | No Reaction. |
| C2O42- | C2O42-(aq) + 16H+(aq)+ 2MnO4–(aq)à2CO2(g)+2Mn2+(aq)+8H2O(l) |
| CO32- | No Reaction. |
| NO3– | No Reaction. |
3) Write the balanced chemical equations for the confirmation test on each anion. Use the same format and follow the same rules, given for the screening tests.
Confirmation Test for Cl-
| Anion | Equations |
| Cl– | AgCl(s) + 2NH3(aq)à Ag(NH3)2+(aq) + Cl–(aq) |
Confirmation Test for Br–
| Anion | Equations |
| Br– | 2Br– (aq) + S2O82-(aq) àBr2(l) +2SO42-(aq) |
Confirmation Test for I–
| Anion | Equations |
| I– | 2I– (aq) + S2O82-(aq) àI2(aq) + 2SO42-(aq) |
| I2(aq) + I–(aq) à I3–(aq) |
Confirmation Test for SO42-
| Anion | Equations |
| SO42- | Ba2+(aq) + SO42-(aq)àBaSO4(s) |
Confirmation Test for C2O42-
| Anion | Equations |
| C2O42- | C2O42- (aq)+ Ca2+(aq) à CaC2O4(s) |
| C2O42-(aq) + MnO4–(aq) + 8H+(aq) àMn2+(aq) + 2CO2(g)+ 4H2O(l) |
Confirmation Test for CO32-
| Anion | Equations |
| CO32- | CO32- (aq) + 2H+(aq) àCO2(g)+ H2O(l) |
| CO2(g) + Ba2+(aq) +2OH–(aq) à BaCO3(s) +H2O(l) |
Confirmation Test for NO3–
| Anion | Equations |
| NO3– | Fe2+(aq) + NO3–(aq) + 4H+(aq) à Fe3+(aq)+ NO(g) + 2H2O(l) |
| Fe2+(aq) + NO(g) à Fe(NO)2+(aq) |
4. Which of the seven anions in this experiment will be the easiest to detect if it is in your unknown? Why do you think this? Justify your opinion with the data you collected.]
I think that the easiest anion out of the seven anions we experimented on that will be the easiest to detect if it was in the unknown would be the iodide ion. It would be easiest to detect because it was easily seen to have a clear reaction with the 18 M sulfuric acid. When comparing tests, it shows that the iodide reacted very violently right away. With the strong reaction that occurs, it helps to detect iodide as the unknown. Another reason why iodide would be one of the easier anions to detect is seen when the confirmation was done on iodide. Iodide had instantly reacted right away with the work solution and changed color instantly. This is why I think that iodide would be one of the easiest anions to detect if it were to be the unknown given.
5. Which of the seven anions in this experiment will be the hardest to detect if it is in your unknown? Why do you think this? Justify your opinion with the data that you collected.
I think that the hardest anion to detect would be the nitrate anion because during the experiment , nitrate did not really react with anything added to it. In test III where a reaction with silver nitrate took place and in test IV where barium chloride and calcium chloride was added the nitrate anion did not show a big reaction to these test, so this shows that the reaction with nitrate anion will be hard to detect and this will affect how hard it is to find this anion.
6. Are all five screening tests necessary to identifying the anion present in the sample? Why or why not? Is one could be eliminated, which one? Justify your opinion with the data you collected.
No I feel that not all five screening tests were necessary to identify the anion present in this sample because I thought that some of them were redundant and found the same results with them. For example the first screen test that uses 3 M sulfuric acid is very similar with the second screen test in which 18 M sulfuric acid was used and because these two test were so similar we were able to skip the 3 M sulfuric acid screening test. Since these two test both use sulfuric acid, I felt that we could find the results with just the 18 M sulfuric acid which would be faster and would take less time. If we were to have proceeded with the screen test I, I would have assumed that the 3M sulfuric acid did not really react with the anions given and not until the 18 M sulfuric acid was used did a reaction occur. If one of these test could be eliminated, I would have to say that test one could be eliminated because test 2 using the 18 M sulfuric acid could result in similar reactions and that 3 M sulfuric acid would be inefficient.
