Ag+(aq) + Cl-(aq) → AgCl(s)
The equipment that will be needed for this experiment is:
- A hot plate
- Weighing bottle
- Stir rod
-
160°C oven
- scoopula
- 250mL beaker
- filter crucible with suction beaker
- wash bottle
- rubber policeman
- analytical balance
Procedure:
Note: This analysis was carried out in duplicate.
1. A 0.25 gram sample of unknown 547 was weighed accurately on an analytical balance using a clean, dry weighing bottle.
2. 0.2638 grams of the unknown was transferred into a 250mL beaker and 100mL of distilled water and was added. A stirring rod was used to dissolve the unknown solid.
3. Five drops of concentrated Nitric Acid (HNO3) was added to the solution to acidify it using an eyedropper.
4. 40mL of 0.1M silver nitrate was added to the solution in attempt to precipitate solid silver chloride. There was a slight excess of silver nitrate added to ensure that all of the silver chloride formed a precipitate.
5. The beaker was then heated using a hot plate until it was nearly boiling. It was left at the near boiling point for 2-3 minutes. This allowed the precipitate to coagulate.
6. The solution was removed form the hot plate and cooled until room temperature.
7. Then an extra drop of silver nitrate solution was added to the solution to see if any further precipitate formed. It did not.
8. A clean dry filter crucible was then weighed on an analytical balance.
9. The solution was then filtered through the crucible. A rubber policeman was used to ensure all the solid was out of the beaker (which would result in weight measurement errors). The remaining solid that was stuck to the beaker, the policeman, and the stirring rod were rinsed off using distilled water into the crucible.
10. 40mL of 0.02M nitric acid was rinsed over the precipitate and through the filter.
11. Then 25mL of acetone was washed over the precipitate and through the filter in attempt to dry it.
12. The precipitate was then placed in an oven at 160ºC for 15 minutes.
13. The crucible was cooled time, then weighed on an analytical balance.
14. The precipitate was places back in the oven for another five minutes, cooled and then reweighed. This step was repeated until the weighings were within 0.002g of the previous.
Observations and Data:
Molar Mass of silver chloride: 107.9 + 35.5 = 143.4g
Calculations:
Run 1 Run 2
1. Mass of silver chloride: 0.5682 ± 0.0002g 0.5274 ± 0.0002g
Mass of chloride ion in
the mass of silver chloride: 0.1407 ± 0.0002g 0.1306 ± 0.0002g
Work for Run 1:
0.5682g AgCl X 1mol AgCl X 1mol Cl X 35.5g Cl = 0.1407 ± 0.0002g Cl
143.4g AgCl 1mol AgCl 1mol Cl
Run 1 Run 2
2. Mass of unknown: 0.2638 ± 0.0002g 0.2539 ± 0.0002g
Percent chloride in
Unknown: 53.34 % 51.44%
Work for Run 1:
% Cl = mass of Cl- = 0.1407 ± 0.0002g X 100 = 53.34 %
mass of unknown 0.2638 ± 0.0002g
Average percentage chloride in unknown: 53.34 + 51.44 = 52.39%
2
Discussion:
The percentage of the chlorine ion in the unknown sample #547 was 52.39%. After finding the weight of the sample and calculating the weight of chlorine in the sample, this percentage was determined.
In this lab, there were a number of possible errors that may have occurred, resulting in an alteration of data. The first common error in data may have occurred by simple human error. There might have been some over or under measuring that could have occurred or some of the sample may have gotten spilled. There may have been some of the silver chloride precipitate still stuck on either the beaker, the rubber policeman or the stirring rod that may not have been washed into the crucible. This would result in a slight error in the weight of the precipitate. Another source of possible error would be that when carrying the crucible, if held in hands rather than in a beaker or tongs, fingerprints and oils from hands may have gotten onto the crucible and would also alter the weight.
Conclusion:
It was found that the unknown sample #547 contained 52.39% of the chloride ion. This was determined by dissolving the sample in distilled water, acidifying the solution, adding silver nitrate to form a precipitate (silver chloride), weighing the precipitate and calculating the mass of chloride present in the silver chloride. Then using the mass of silver chloride and the mass of the unknown sample, the percentage of chloride ion present in the sample was calculated.
