Question

EXPERIMENT #6 DETERMINATION OF THE CONCENTRATION OF TARTARIC ACID IN WINE

1. Why must the sodium hydroxide concentration be reported to four significant figures? Why not use only two significant figures?

2. In the procedure, you added approximately 15 mL of water to each Erlenmeyer flask. Why did the exact volume of water not matter? What impact would accidentally adding 17 mL of water have on the results? Be prepared to explain.

3. Explain the significance of the value for relative standard deviation in the context of this experiment.

4. Explain the significance of the value for percent error in the context of this experiment.

5. The stoichiometric ratio in this experiment is 1:2. Determine how the calculation set-ups would change for the reaction between:

HNO3 (aq) + NaOH (aq) = H2O (l) + NaNO3 (aq) OR

H3C5H5O6 (aq) + 3 NaOH (aq) = 3 H2O (l) + Na3C5H5O6 (aq)

Answer 1

Experiment : determination of tartaric acid concentration by titration.

1. Sodium hydroxide is a hygroscopic salt. It absorbs moisture upon standing in air. Thus to minimize this error one must weight the sodium hydroxide to 4 significant figures for absolute reading.

2. In the method, the amount of water added to tartaric acid solution does not matter as the number of moles of tartaric acid present remains unchanged and is independent of the volume of solution.

3. Relative standard deviation in the experiment would ensure the values we obtain at the end have minimal error associated with it. The error values are taken care of by calculating the standard deviation of the trial runs.

4. Percent error for the experiment would be the value expected with respect to the value obtained in the experiment. The smaller is the percent error the more accurate is the value calculated and purer is the sample taken for measurement.

5. The stoichiometric ratio between HNO3 (monoprotic acid) and NaOH (base ) is 1 : 1.

On the other hand, the stoichiometric ratio between H3C5H5O6 (tripotic acid) and NaOH (base) is 1 : 3.