CHM 144M Section C

Dr. Zhu

Charles Dotse

Aileen Decker

8 October 2015

The Quantitative Determination of an Acid in Carbonated Beverages

Abstract:

The basis of this lab was to juxtapose two different titration methods in their ability to identify the end point, calculate the molarity of citric acid in the two sodas, and apprehend the differences between polyprotic and monoprotic acids. In order to accomplish this, a traditional titration, with phenolphthalein, and a modern titration, with a pH probe, were executed. Through the use of the equation for molarity and stoichiometry, the molarity of citric acid was able to be calculated from V_NaOH, which was found in the traditional titration by subtracting Vi from Vf and

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Use a 20ml volumetric pipet to measure the required volume of decarbonated soda and put it in a 250ml beaker. Add distilled water using a graduated cylinder. Place pH probe in the soda solution. Put beaker on a magnetic stir plate (keep probe away from the stirrer). Fill buret and align the tip right above the drop counter. Record the initial volume of NaOH (Vi). Turn on the stir plate to 300rpm and program Measurenet. Carefully open stopcock so it drips at 1 drop per second. Stop the titration when the pH reaches 10.5. Save data and repeat this process 2 more times. Record the final volume (Vf) as well as the volume of the soda sample. Remove probe and rinse it with distilled water. Put it back in the storage solution. Then, perform all proper

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Table 3: Modern Titration Values (Jones Green Apple)

Trial Initial Volume (Vi) Final Volume (Vf) Volume of Soda (Jones Green Apple) Volume of NaOH Used (Vf-Vi)

1 0.4ml 24.30ml 20.0ml 23.9ml

2 o.oml 24.60ml 20.0ml 24.60ml

3 0.0ml 24.60ml 20.0ml 24.60ml

These values are used in the calculation of the molarity of citric acid.

Table 4: Modern Titration Molarity, Mean, and Standard Deviation Values (Jones Green Apple)

Trial Molarity of Citric Acid (Jones Green Apple)

1 0.0151

2 0.0147

3 0.0148

Mean Molarity: (∑▒X)/n Standard Deviation: √((∑▒(mean-x)^2 )/(n-1))

0.0149 2.12 X 〖10〗^(-4)

Finding the standard deviation and mean of the molarity of citric acid displays the modern titration’s precision in finding the endpoint.

Figure 1: Titration Curve

By finding the y-coordinate corresponding to the V_NaOH, x-coordinate from the first derivative graph, the pH at the end point is