Determining the Percent Composition of Iron in an Unknown Salt

Abstract

In this lab, the percent composition of iron was found in a sample of an unknown ferric salt mixture. With the use of a burette, titration was used to add EDTA (the titrant) to the Fe3+ salt mixture until the solution changed from a dark purple to a light yellow. The dark purple is the iron-salicylate complex but EDTA, creates salicylate ions, creating the light-yellow color. The reaction is as follows: [Fe(HOC6H4 COO)3](aq) + H2C10H12N2O82- (aq) –> Fe(C10H12N2O8)(aq) + 2H+(aq) + 3HOC6H4COO-(aq).

This reaction demonstrates how the salicylate ions are originally a dark purple color but when EDTA is added, a light-yellow color and free salicylic ions are produced. This change from purple to yellow indicates an endpoint, allowing for the calculation of Fe3+ in the solution from the known concentration and volume of EDTA. Lastly, the means, standard deviations, and mole values of the titration samples in Erlenmeyer flasks were calculated to find the mass of EDTA and the percent composition of Fe3+ in the unknown ferric salt.

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The percent composition of Fe3+ in the unknown ferric mixture was 16.02039971% and the RSD% was 4.464636719%. However, the percent relative standard deviation turned out to be greater than 0.5%, the experimental titration performance was poor. This error can be resolved by utilizing better titration techniques as EDTA could have been added to the salicylate slower- allowing for more precise data.

Experimental Data

Procedure Overview

1. Titration of Fe3+ salt mixture with EDTA until a color change from dark purple to light yellow was observed.
2. Calculation of mean, standard deviations, and mole values from titration samples to find the mass of EDTA and percent composition of Fe3+.

Results Analysis

The titration method effectively determined the Fe3+ concentration, yielding a percent composition of 16.02%. The relatively high %RSD indicates a potential for improved precision in future titrations.

Sample Calculation

The percent composition was calculated using the formula:

% composition = (mass of Fe(III) titrated by V mL of EDTA) / (Mass of sample transferred in 25.00-mL pipette) * (100)

% composition = (0.014576962) / (0.09099 g) * 100

% composition = 16.02039971%

The %RSD was calculated as:

%RSD = (Sv/V) * 100%

%RSD = ((0.565803411 mL)/(12.673 mL)) * 100%

%RSD = 4.464636716%

The percent relative standard deviation yielded was 4.464636716, much higher than the given percent relative standard deviation of 0.5%. This 4.46% relative standard deviation is a lot higher than 0.5%, showing that the experimental data was very inaccurate. The titration proved to be poor as the percent relative standard deviation was extremely high.

An indicator in this titration was useful as the indicator allowed for the determination of how much Fe (III) was present in the unknown ferric mixture. The absence of the indicator would turn into the light-yellow color from the dark purple color, letting the solution to remain the dark purple color. It would be unknown at what amounts of EDTA titrated the Fe (III) in the salt mixture. The absence of the indicator would have led to an unknown percentage of iron present in the ferric salt, resulting in an unsuccessful experiment.

The net ionic equation is:

CH3COOH(aq) + OH-(aq) CH3COO-(aq) + H2O(l)

The consequence if an indicator forms a stronger complex with the Fe3+ than the FeEDTA- complex would be that no color change from a dark purple to a light-yellow would have been observed. The EDTA would not have been able to titrate the Fe3+.The reaction would not become a light-yellow color and hence, changing the reaction. In addition to no observed color change, the percent composition of iron would not have been found.

Discussion

The %RSD value of 4.464636716% indicates a deviation from optimal precision, suggesting the need for enhanced titration techniques. The color change facilitated by the indicator was crucial for determining the endpoint of the titration, directly impacting the accuracy of Fe3+ quantification.

Conclusion

This experiment demonstrated the utility of titration in determining the percent composition of iron in a ferric salt mixture. The calculated iron composition was 16.02039971%, with a %RSD of 4.464636719%, indicating a margin for methodological improvement. Future experiments should focus on refining titration techniques to reduce variability and improve the accuracy of the determined percent composition.