Redox Titration of Mohr's Salt Solution With Potassium Permanganate

Introduction

Titration is a process in which the concentration of an unknown acid or base is determined using the known molarity of another acid or base. This process includes taking a solution, known as the titrant, and slowly adding it to the unknown solution -the sample- through the use of a burette. The volume and molarity of the solution in the burette is known and is used to determine the unknown molarity of the substance in the Erlenmeyer flask.

The point at which the titration can be flagged as complete, is called the equivalence point. This is an indication that at that point, the moles of the titrant equal the moles of the solution in the flask. This point is also followed by a change in the sample solution’s color, pH, etc, and is called the endpoint of the titration. As such, the purpose of this lab was to determine the unknown molarity of Mohr’s salt solution by titrating it with potassium permanganate. The end point of this titration was observed when the colorless solution displayed a permanent faint pink color.

As well as using titrations for determining the unknown molarity of a substance, titrations can also be used to create a balance in pH levels in certain industries. One example of this is in commercial aquariums. Aquariums around the world use titrations to test the water pH levels and concentrations of elements such as ammonia in the water, to create a balance that can sustain marine life. Titration is relied upon heavily here because it is a matter of life and death and if they want to continue to allow large amounts of fish to live there, the water must contain a balance of the elements and the acidic or basic substances that are present in it. That being so, titration is a crucial process in this particular industry because of the part it plays in helping sustain the lives of many underwater sea creatures (What Are the Real Life Uses of Titration?).

Discussion

The titration of Mohr’s salt with standardized potassium permanganate solution was done to determine the concentration of the Mohr’s salt in the flask. The goal of the experiment was to pipette potassium permanganate solution into the salt solution drop by drop, until the endpoint was observed, where there would be a visible permanent faint pink color.

After observing a dark pink solution in trial one and four, light pink solutions were derived in both the second and third trials. This was an indication that just the right amount of potassium permanganate was added to the Mohr’s salt which caused it to change into the faint pink color. When using these values to find the molarity for the Mohr’s salt, the results were precise and very close to the actual concentration of the salt solution. However in trials one and four, the intensity of the solution was a dark pink. This indicated that too much of the potassium permanganate was added to the salt solution which caused it to display a dark pink colored solution. As for the results for trials one and four, the results were not very accurate and after calculations were done, they displayed higher concentrations for the salt solution than what was expected. This was due to the number of errors that could have taken place during the lab.

In this experiment, some accidents did occur, where the titrant was dropped into the sample far faster than it should have been, and thus most likely caused the solution to change to a dark pink before it had the chance to display a faint pink color. In titrations, one drop can make a big difference and as such, there was a point in the lab where the drops were falling too fast and so it caused the color to go straightaway to dark pink. This also meant that we had added too much KMnO4 and the calculations would show the molarity of the Mohr’s salt higher than expected. To avoid this problem in the future, it is best to set the tip so that it causes the drops to fall one by one and not at a very fast rate. This will allow the individual to be able to stop the drops right away if they start to see a faint pink color. Another source of error is either not rinsing the buret tube before the titration or rinsing it with the wrong solution.

First, not rinsing it with the correct solution could potentially cause it to react with the substance inside the tube, which could ultimately hinder the whole experiment and produce completely adverse results and an error in the titration. Also, rinsing the tube with the wrong solution can cause a reaction inside the burette and create a whole other set of problems, thus affecting the results of the titration. To avoid these errors, it is best to clean all the equipment beforehand, and also to pay attention to the solutions that are being used. Since most of them are colorless, it can be hard to tell them apart, and so it is best to pay attention. However, the percent error for this titration was 2.21%. Although this is a relatively low value, the goal is always to have a percentage less than 1 or none at all. Either one of the sources of error described above could have potentially affected the titration results, however, the experiment went well, with some hiccups along the way.

Conclusion

To conclude, the titration experiment yielded relatively expected results. Using the potassium permanganate, Mohr’s salt was titrated and its concentration values were determined using the data retrieved from the lab. The concentration values that were determined from the lab, proved to be very close to the actual concentration. Although there were some errors, the experiment proved to be a success.