Report sheet Exp. 8 Phosphoric Acid in Cola Name: Partner\'s name: Date: Lab Sec
ID: 572504 • Letter: R
Question
Report sheet Exp. 8 Phosphoric Acid in Cola Name: Partner's name: Date: Lab Section: 2. What are the percent errors for your values of Kai and Kai? %Error Kar %Error Ka, 3. If your percent error is greater than 10%, explain what would contribute to such a large percent error. If you had less than 10% error. Explain what techniques you employed to obtain such a small error. 4. A carbonated beverage maker claims that none of their colas contain more than 30 mg of phosphorus per 6-oz serving. Calculate the mg of phosphorous in a 6- oz serving of cola, according to your experimental data. I fl. Oz -29.5735 mL 5. Explain why the cola that you used in this experiment has to be flat" with all the carbonation removed. What would happen if the cola was not flat?Explanation / Answer
H3PO4 titration with NaOH
2. Percent error
pKa1 by graph = 4.2
literature pKa1 = 2.15
%error = (4.2 - 2.15) x 100/4.2 = 48.81%
pKa2 by graph = 6.7
literature pKa1 = 7.2
%error = (7.2 - 6.7) x 100/7.2 = 6.94%
3. the error in pKa2 is large. The reason could be incorrect measurement of the titration end point. We may have added excess NaOH so the pKa1 also shifts.
4. 6 oz = 6 x 29.5735 ml
= 177.441 ml
From titration,
moles of P = moles H3PO4
= 0.05 M x 2.3 ml
= 0.115 mmol
mg of P in 6 oz serving = 0.115 mmol x 98 g/mol = 11.27 mg
5. The cola has to be flat as the CO2 was released from the system by opening the cork of the bottle.
Formulas,
moles = molarity (M) x volume (L)
grams = moles x molar mass