Lab Report 11.pdf

# This table shows the recorded values for titration of

• Lab Report
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2. This table shows the recorded values for titration of acetic acid against NaOH using a pH meter. V-base V-base refers to volume of NaOH titrated. CpH/CV refers to change in pH divided by change in Volume. One example calculation of CpH/CV can be done for the first reading: CpH/cV = (3.35-3.04) / (1.13-0) = 0.27. V-base (mL) pH of solution CpH/CV (mL^-1) 0.0 3.04 ... 1.13 3.35 0.27 2.60 3.63 0.19 5.56 4.01 0.13 8.29 4.28 0.099 11.98 4.59 0.084 15.45 4.90 0.089 17.90 5.18 0.11 19.64 5.47 0.17 20.90 5.78 0.25 21.53 6.09 0.49 21.95 6.37 0.67 22.20 6.69 1.28 22.30 6.94 2.50

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22.42 22.60 7.26 9.05 2.67 9.94 22.62 9.30 12.5 22.80 9.58 2 22.85 9.83 5 23.00 10.13 2 Continued 23.20 10.37 1.2 23.50 10.65 .93 24.98 10.93 .58 25.08 11.22 .26 27.21 11.51 .14
3. The point at which CpH/CV reaches its maximum is at a value of 12.5, where pH= 9.30 and volume of NaOH is 22.62. 4. [HOAc]= (22.62 mL)*(0.22 M) / (25 mL--this is the original volume of HCl)= .20 M 5. pH is the pKa at half equilibrium point, which is 9.30/2= 4.65. The pKa for HOAc is 4.65, and the accepted value according to the lab manual is 4.75. Percent error= absolute value of ((4.65-4.75) / (4.75))*100%= 2.11% error Percent error for closest recorded value= 3.37% Discussion Questions 1. The major difference is the fact that because HOAc is a weak acid, it will only dissociate slightly while HCl, which is a strong acid, will dissociate completely. Also the pH at equivalence point is lower for titration with HCl since it is a stronger acid. 2. Buffers maintain small pH changes in a solution where a strong acid or base is involved. When the basic buffer was tested, the solution remained basic, responding with miniscule pH changes, staying within the range of 8.79-9.61. When the neutral buffer was tested, the solution remained abnormally basic, perhaps because our acidic and basic buffers weren’t neutralized before adding them together.

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