Neutralization Titrations: The Determination of Soda Ash

I.Purpose: The goal of this experiment is to determine the weight % of Na2CO3 through the preparation of NaOH and HCl standards. The molarity of the requirements will be discovered through titration of KHP for NaOH, HCl vs the known NaOH, and the unknown Soda Ash sample vs the known HCl.

II.Equations and Sample Estimations:

Titration of HCl with NaOH:
Total Formula:
HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq).

Net Ionic Formula:.
H+ + OH- H2O( l).

Calculations (10mL 0.1 M HCL, 100mL H20, 7.8 mL NaOH):.

# mols NaOH = 0.1 M (recognized concentration) x 0.0078 L (titrated volume) = 0.00078 mol.

1:1 ratio mol NaOH to HCL = 0.00078 mol HCl.

M HCl= = 0.078 M HCl.

Standardization of NaOH vs KHP.
Complete Equation:.
NaOH + KHC8H4O4 KNaC8H4O4 + WATER.

Net Ionic Equation:.
OH- + HC8H4O4- C8H4O42- + H20.

Estimations (0.3291 g KHP, 18mL NaOH):.

# mols/M NaOH: = = 0.089 M NaOH.

Decision of the Unknown Soda Ash Sample (Unidentified # 67): Total Equation: Na2CO3 (aq) + 2HCl CO2 (g) + WATER (l) + 2NaCl (aq).

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Net Ionic Equation:.
CO32- + 2H+ WATER + CO2.

Estimations (0.1887 g Soda Ash, reaction finished with 22.80 mL HCL total):.

#mols HCL = 0.0228 L x 0.078 M (standardized HCL M) = 0.00117 mol #moles Na2CO3 = 2:1 HCl: Na2CO3= = 0.00089 mol.
Grams Na2CO3 = 0.00089 mol x 106.0 g/mol = 0.094 g.

% Na2CO3 by wt = X 100 = 49.94%.
III.Data and Results.
All titrations finished with micropipette # 8. All masses found utilizing balance # 16.

Standardization of HCl with NaOH
10mL 0.1M HCl diluted in 100mL H2O, Titrated with NaOH

Volume NaOH (mL)Description of Color at volume added
Flask #17.8Dark pink, fast change
Flask #27.85Light pink, fast change
Flask #37.9Light pink, slow change

Mean Volume NaOH: 7.85 mL
SD: 0.05
RSD: 0.64%
Standardization of 0.1M NaOH
Quantity of KHP added to 100mL H20, Phenolphthalein indicator then titrated with NaOH

Weight KHP (g)Volume NaOH
(mL)Molarity NaOH in titration
Flask #10.3291180.0895M
Flask #20.207211.20.0893M
Flask #30.246113.40.0894M
Mean Molarity: 0.0894 M
SD: 7.071 x 10-5
RSD: 0.07%

Determination of the Unknown (#67) Soda Ash Sample
Quantity of Soda Ash sample added to 50mL H20, Phenolphthalein indicator then titrated with HCl to the first equivalence point (Eq). Methyl Orange indicator added for second Eq.

Weight Soda Ash (g)Volume HCl (mL) Eq Point 1Volume HCl (mL) Eq Point 2Total Volume HCl (mL)% Na2CO3 in Soda Ash Sample Flask #10.229914.51428.551.24
Flask #20.14218.88.7517.651.20
Flask #30.188711.511.7522.849.94

Mean % Na2CO3 by weight: 50.79%
SD: 0.74%
RSD: 1.45%

IV.Conclusion

The standardization of both HCl and NaOH yielded Relative Standard Deviations of 0.64% and 0.07% respectively. Following the procedure for the determination of the Soda Ash sample utilizing these standards provided for an accurate and precise measurement of the Na2CO3 weight percentage. Given the data collected and calculations performed, unknown Soda Ash sample #67 is approximately 50.79% Na2CO3 by weight with a 95% confidence interval of 50.79% 1.66%.

This value, however, has a distinct possibility of being incorrect or off target due to error such as incorrect calibration/use of the micropipettes for titration, either personal or environmental error in the weigh by difference method on the analytical balances, or the possibility of having trouble with differentiating the different equivalence points by color during titration. Overall, as long as there was no unforeseen outside influences on the procedure, the values determined are well within the 95% confidence interval and thus can be accepted.