Identification of an Organic Acid

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Discussion: The average NaOH concentration was 9.465x10-2 M NaOH. Since 1 mole of NaOH = 1 moles of KHP, there is a 1:1 ratio of moles of KHP and NaOH (GSU Lab Manual 32).

Titration of 10.00 mL HCL with 9.465x10-2 M NaOH

Trail

1

2

3

NaOH Vi

0.00 mL

21.20 mL

23.40 mL

NaOH Vf

21.00 mL

42.20 mL

44.25 mL

Volume of NaOH used

21.00 mL

21.00 mL

20.85 mL

mol NaOH

1.99x10-3 mol

1.99x10-3 mol

1.97x10-3 mol

mol HCL

1.99x10-3 mol

1.99x10-3 mol

1.97x10-3 mol

Concentration HCL

1.99x10-1 M

1.99x10-1 M

1.97x10-3 M

Calculations:

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Discussion: The moles of NaOH was found to be 1.99x10-3 moles. Since 1 mole of NaOH = 1 moles of HCL, there is a 1:1 ratio of moles of HCL and moles of NaOH, aiding in the calculation of the molarity of HCL (GSU Lab Manual 32). The average molarity of HCL was 1.98 x10- 1 M.

Titration of Unknown Acid with 9.465x10-2 M NaOH

Trial

1

2

3

Mass Unknown Acid

0.2992g

0.2906g

0.2952g

Volume NaOH used

16.50 mL

16.00 mL

16.13 mL

Volume NaOH corrected

0.01650 L

0.01550 L

0.01563 L

mol OH-

0.0156 mol

0.0147 mol

0.0148 mol

Equivalent Weight

191.6 g/mol

198.3 g/mol

199.5 g/mol

Calculations

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Discussion: The final solvent for the unknown acid was a 2:1 ethanol and water ratio. The average equivalent weight of the unknown organic acid is about 196.47 g/mol.

Sodium Fusion Test:

Observation

Results

Nitrogen test

Clear solution

Negative for Nitrogen

Halogen test

White precipitation

Positive for Halogen

Discussion: A clear solution was observed during the Nitrogen test, concluding that the results were negative for the presence of nitrogen. A white precipitation was observed in the Halogen test, resulting in a positive result for the presence of a halogen (Cl-, Br-, or I-).

Conclusion: After comparing the data obtained from this series of experiments to the computer search, the unknown organic acid #8122361-HF-15 has been identified to be 2,4-dichlorobenzoic acid, Cl2C6H3COOH. The experimental melting point of the unknown acid was determined to be 168˚C - 171˚C and the average equivalent weight of the unknown organic acid is about 196.47 g/mol. The determining factor that narrowed down the results to from three to one was the sodium fusion test which had tested positive result for a halogen. Two of the three possible organic acid were easily eliminated since they did not contain a halogen in their formulas. That left only 2,4-dichlorobenzoic acid, Cl2C6H3COOH as a possible organic acid with a chloride halogen present. From the results of the experiment, the unknown acid had a melting point of 168˚C - 171˚C and a equivalent weight of 196.47 g/mol, which are in close range of the melting point (164 ˚C -165 ˚C) and equivalent weight (191 g/mol) of 2,4-dichlorobenzoic acid. The percent deviation calculated of each data set were insignificantly low, which means the data is accurate and therefore effective.

Appendix:

Results of your search for organic acids with:

Melting Point:

166 ± 7 oC

Equivalent Weight:

191 ± 15 g/eq

Chemical Name

Formula

Melting Point

(oC)

Equivalent Weight

(g/eq)

Amide Melting Point

(oC)

pka1

4-tert-butylbenzoic acid

(CH3)3CC6H4COOH