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Neutralization Titrations: The Determination of Soda Ash Essay

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 standards will be found 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 Calculations:

Titration of HCl with NaOH:
Complete Equation:
HCl (aq) + NaOH (aq)  H2O (l) + NaCl (aq)

Net Ionic Equation:
H+ + OH-  H2O(l)

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

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

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 + H2O

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

Calculations (0.3291g KHP, 18mL NaOH):

# mols/M NaOH: = = 0.089M NaOH

Determination of the Unknown Soda Ash Sample (Unknown # 67): Complete Equation: Na2CO3 (aq) + 2HCl  CO2 (g) + H2O (l) + 2NaCl (aq)

Net Ionic Equation:
CO32- + 2H+  H2O + CO2

Calculations (0.1887g Soda Ash, reaction completed with 22.80mL HCL total):

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

% Na2CO3 by wt = X 100 = 49.94%
III.Data and Results
All titrations done with micropipette #8. All masses found using 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.


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