Lab Report: Determination of Na2CO3 Weight Percentage

Categories: Chemistry

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Abstract

The purpose of this experiment was to determine the weight percentage of Na2CO3 in an unknown soda ash sample (#67). This was achieved through the standardization of NaOH and HCl solutions, followed by titration of the soda ash sample against the standardized HCl. The standardization process yielded precise results with relative standard deviations of 0.07% for NaOH and 0.64% for HCl. The determination of the unknown soda ash sample revealed a weight percentage of approximately 50.79% Na2CO3 with a 95% confidence interval of 50.

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79% ± 1.66%. Despite potential sources of error, the results are within an acceptable range and can be considered accurate.

Introduction

The goal of this experiment is to determine the weight percentage of Na2CO3 in an unknown soda ash sample (#67) by performing a series of titrations and standardizations. To achieve this, we standardized both NaOH and HCl solutions and then utilized these standardized solutions to titrate the soda ash sample. The weight percentage of Na2CO3 was calculated based on the amount of HCl consumed during the titration.

The accuracy and precision of the results were assessed through relative standard deviations.

Materials and Methods

Titration of HCl with NaOH:

The reaction involved in this titration is as follows:

HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)

The net ionic equation is:

H+ + OH- → H2O (l)

Calculations for this titration:

Moles of NaOH = 0.

1 M (known concentration) x 0.0078 L (titrated volume) = 0.00078 mol

Moles of HCl = 1:1 ratio with NaOH = 0.00078 mol HCl

Molarity of HCl = 0.078 M HCl

Standardization of NaOH vs. KHP:

The reaction involved in this standardization is as follows:

NaOH + KHC8H4O4 → KNaC8H4O4 + H2O

The net ionic equation is:

OH- + HC8H4O4- → C8H4O42- + H2O

Calculations for this standardization:

Moles of NaOH = 0.089 M

Determination of the Unknown Soda Ash Sample (#67):

The reaction involved in this determination is as follows:

Na2CO3 (aq) + 2HCl → CO2 (g) + H2O (l) + 2NaCl (aq)

The net ionic equation is:

CO32- + 2H+ → H2O + CO2

Calculations for this determination:

Moles of Na2CO3 = 0.00089 mol

Weight of Na2CO3 = 0.094 g

Weight percentage of Na2CO3 = 49.94%

Data and Results

All titrations were conducted using micropipette #8, and all mass measurements were performed with balance #16.

Standardization of HCl with NaOH

Volume NaOH (mL)	Description of Color at Volume Added
7.8	Dark pink, fast change
7.85	Light pink, fast change
7.9	Light pink, slow change

Mean Volume NaOH: 7.85 mL

Standard Deviation (SD): 0.05

Relative Standard Deviation (RSD): 0.64%

Standardization of 0.1 M NaOH

Weight KHP (g)	Volume NaOH (mL)	Molarity NaOH in Titration
0.3291	18.0	0.0895 M
0.2072	11.2	0.0893 M
0.2461	13.4	0.0894 M

Mean Molarity: 0.0894 M

Standard Deviation (SD): 7.071 x 10^-5

Relative Standard Deviation (RSD): 0.07%

Determination of the Unknown (#67) Soda Ash Sample

Weight Soda Ash (g)	Volume HCl (mL) Eq Point 1	Volume HCl (mL) Eq Point 2	Total Volume HCl (mL)	% Na2CO3 in Soda Ash Sample
0.2299	14.5	14.5	28.5	51.24%
0.1421	8.8	8.75	17.65	51.20%
0.1887	11.5	11.75	22.85	49.94%

Mean % Na2CO3 by weight: 50.79%

Standard Deviation (SD): 0.74%

Relative Standard Deviation (RSD): 1.45%

Discussion

The standardization of both HCl and NaOH solutions demonstrated high precision with relative standard deviations of 0.64% and 0.07%, respectively. These results indicate that the concentrations of the solutions were accurately determined. The determination of the unknown soda ash sample (#67) revealed a weight percentage of approximately 50.79% Na2CO3, with a narrow 95% confidence interval of 50.79% ± 1.66%. This suggests that the method used was both accurate and precise.

Potential sources of error in this experiment include possible inaccuracies in the calibration and use of micropipettes for titration, errors in the weigh-by-difference method when measuring the soda ash sample, and difficulties in distinguishing between different equivalence points by color during titration. Despite these potential sources of error, the results obtained fall well within the 95% confidence interval, indicating the reliability of the findings.

Conclusion

In conclusion, the standardization of NaOH and HCl solutions followed by the titration of the unknown soda ash sample (#67) allowed for the determination of its Na2CO3 weight percentage with high precision. The results suggest that the sample contains approximately 50.79% Na2CO3 by weight, with a 95% confidence interval of 50.79% ± 1.66%. The experiment demonstrated the accuracy and reliability of the analytical techniques employed, despite potential sources of error.

Recommendations

For future experiments, it is recommended to pay close attention to the calibration and proper use of micropipettes to minimize potential errors during titration. Additionally, further investigation into methods to improve the distinction between equivalence points during titration could enhance the accuracy of results. Overall, the experiment provided valuable insights into the determination of Na2CO3 weight percentage and the standardization of solutions for analytical chemistry applications.