Exp. 3 - Course Chem 221 Name Ashay Mehta Experiment#3...

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Course: Chem 221 Name: Ashay Mehta Experiment #3 – Determination of the Percentage of Na 2 CO 3 in a Sample Unknown Number: #392/372 Due Date: 10/9/09 Date Report Submitted: 10/9/09 Grade: Accuracy Presentation Total
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Determination of the Percentage of Na 2 CO 3 in a Sample Ashay Mehta October 7 th , 2009 Objective: To successfully titrate solutions and to find out the percentage of Na 2 CO 3 in an unknown sample using the indicator and pH probe methods. Theory: Using two different titration methods, HCl dissociates to form H + and Cl - . Carbonate in aqueous solution acts as a base. It accepts a proton from the bicarbonate. CO 3 2- + H + HCO 3 - Then the bicarbonate combines with another H + to form H 2 CO 3. HCO 3 - + H + H 2 CO 3 Using these equations, we can find the equilibrium equations for both. The equilibrium equations can be used to find the pH at different points on the titration curve which is a plot of the pH versus the amount of titrant added. Since we want to have a more accurate reading, we use the second end point where H 2 CO 3 dissociates to CO 2 . H 2 CO 3 H 2 O + CO 2 The solution is boiled to rid it of CO 2. As the carbonic acid is removed, the pH is controlled by a small concentration of HCO 3 - which is basic. If titration is resumed, the pH decreases rapidly since the concentration of carbonic acid is small. The indicator then gives a sharp color change from blue to yellow. Procedure: First, I weighed the container. Then I weighed both the known Na 2 CO 3 sample and the container in order to get 0.2500 grams. I did this three times. Then I poured out each sample into three separate Erlenmeyer flasks. After that, I added 50 mL of distilled water and swirled until the salt was dissolved. Then I added 4 drops of the indicator, bromocresol green. Using the HCl as the titrant, I titrated the solution until it
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Exp. 3 - Course Chem 221 Name Ashay Mehta Experiment#3...

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