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lab 9 - acid CH 3 COOH(aq ↔CH 3 COO(aq H(aq the K a was...

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Lab #9 Purpose: The purpose of this lab is to find values of acid ionization constants by measuring the pH. Also we learn to prepare buffer solutions and observe their resistance to pH change. Procedure: In part I we found K a of acetic acid by using a pH meter to find the titration curve and compared it to the correct K a , 1.76E-5. We found the K a to be 2.0*10E-5. Errors could have been caused by not adding 1mL at a time but instead adding a little over or under each time. This error would have thrown off the ability to tell when the pH was increasing rapidly, thus changing the mLs needed to reach the half equivalence point and equivalence point. For part II we found the dissociation constant of acetic acid in different solutions. First we had 10mL of acetic acid, and found the K a to be 1.00317E-5. This error could be attributed to an error in the pH meter. When 25mL of NaA were added to 10mL of acetic
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Unformatted text preview: acid CH 3 COOH (aq) ↔CH 3 COO-(aq) +H + (aq) the K a was 3.15E-5. This discrepancy could be because of a not quite mixed solution, causing the pH to be too high. Next we had 5mL of NaA and 30mL of acetic acid. This time the K a was 2.098E-6. This could again be because the solution wasn’t mixed together all the way. In part III we found the buffering capacity of a buffer solution compared to an unbuffered solution. When a strong acid was added to an unbuffered solution the pH decreased from 7 to 1.4 and when a strong base was added the pH went to 12.1. In a buffered solution the pH when acid was added was from 4.5 (sometimes DI water is slightly acidic) to 4.4. And when a strong base was added it went from 4.5 to 4.7. The buffered solution resisted pH change much better than the unbuffered....
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