Olivia SzydlikGeffrey Torres Morales
Chem 117: Section 31L, TA Genevieve Asselin
9 November 2018
Lab 7; Volumetric Iron Analysis
Titrations are used to be able to determine the concentration of a certain substance in a solution. In this experiment, we had the task of finding the concentration of iron in an unknown salt. Using titration and indicators, we were able to see when the reaction neutralizes when the color of the solution changed. The results of the titration gave us endpoints of 10.44ml and 11.42ml for the concentration. Some likely sources of error would come from the amount of EDTA that is added into the solution until the color changes and well as the amount of ferric salt that was added to the dilution of. Another error is that the EDTA was stronger than the indicator so that was the reason why there was a color change. The purpose of this experiment is to be able to practice using titrations as well as familiarize volumetric flasks and be able to create dilutions for solutions.
This table below shows the calculations made during the experiment.
EDTA concentration 0.02060 M
Mass of salt transferred into 25.00ml pipette 0.10010g
Titration of sample endpoint #1 10.44mL
Titration of sample endpoint #2 10.28mL
Titration of sample endpoint #3 9.68mL
Mean of endpoint volumes V = 10.13mL
Standard Deviation .4007mL
Millimoles of EDTA in volume V 0.2087 mmol
Millimoles of Fe(lll) titrated by Vml of EDTA 0.2087 mmol Fe(lll)
Mass of Fe(lll) titrated by Vml of EDTA 0.01165 g Fe(lll)
Percent Fe(lll) in ferric salt 11.64%
Millimoles of EDTA in the volume V;
10.13mL × 0.0206 mol EDTA1 L solution×1 L 1000mL×1000mmol1 mol =0.2087 millimolesMillimoles titrated;
0.2087mmol×1 mol1000mmol×55.845g1 mol Fe3+=0.01165 g Fe3+Percent composition;
0.01165 g Fe3+0.10010 g× 100%=11.64% Discussion Questions
% RSD=0.4007mL11.53ml× 100%= 3.5%The RSD percentage is about 3.5% with the calculation that were drawn. Since the technician is expected to perform the titration under 0.5%, it is close to the actual data that has been drawn. There is a little of a percent error of the experimental results due to the titrations that were measured within the experiment.
It is useful to use an indicator in the titration because it shows color change when there is a reaction occurring within the solution. In this experiment, the color changed when the acid that is formed with this reaction is eaten up and is neutralized. The consequence if the indicator was not used would be that too much EDTA would be poured into the solution and it would be impossible for it to be able to figure out the concentration of the iron in the unknown salt that was diluted.
The net ionic equation for the reaction is;
2H+2Na=2Na+H2The consequence if an indicator was chosen that forms a stronger complex with Fe3+ would be that it wouldn’t be able to change color. Since it is stronger than the Fe-EDTA, the indicator would not be able to react with the EDTA solution so as said, it would not be able to change color so that you could be able to calculate the concentration.
Chem 117 Lab Manual