1. Distinguish between the following pairs of terms as they pertain to this expe
ID: 557892 • Letter: 1
Question
1. Distinguish between the following pairs of terms as they pertain to this experiment. (a) monoprotic and diprotic acids (b) equivalence point and end point of a titration (c) half-equivalence point and equivalence point of a titration 2. Following the Procedure of this experiment, a student titrated 0.653 g of an unknown weak, monoprotic acid with 0.100M NaOH and monitored the titration with a pH meter. Her titration data were: volume of volume of NaOH solution NaOH solution added.ml added mL p 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 3.30 4.22 4.55 4.76 4.92 5.06 5.18 5.29 5.40 5.51 5.62 22.00 5.74 24.00 5.88 26.00 6.03 28.00 6.24 30.00 6.57 31.00 6.89 32.00 8.99 33.00 11.08 34.00 11.38 36.00 11.67 38.00 11.83 (a) Prepare a titration curve of this student data using the Logger Pro software as instructed on pages 89-90 of this experiment. (If you are having problems downloading Logger Pro, use Excel) Determine the mL of NaOH solution used at the equivalence point. Attach the pH curve and 1st derivative plots to this pre-lab assignment.Explanation / Answer
1a) Monoprotic acids are acids that can release only one proton in aqueous solution and have one equivalence point. Eg. HCl and HNO3
HCl (aq) -------> H+ + Cl-
Diprotic acids are acids that can donate two protons in aqueous solution and have two equivalence points. Eg. H2SO4 and H2CO3
H2SO4 (aq) ------> H++ HSO4- Ka1 = 1.0 x 10^3
HSO4- (aq) ------> H+ + SO42- Ka2 = 1.2 x 10^-2
b) Equivalence point: In a titration, the equivalence point is the point when the amount of titrant added is enough to completely neutralize the analyte solution. At the equivalence point, the moles of acid are equal to the moles of base in the stoichiometric ratio.
The endpoint: endpoint is that point at which the indicator changes color in a colorimetric titration. For a strong acid and a strong base such, when the final solution is neutral, indicators will change color at the equivalence point but for a weak base and a strong acid or strong base and a weak acid the final solution will not be neutral, indicators will not change color at the equivalence point.
c.
Half Equivalence Point: When a reaction in titration reaches to the half way. At half equivalence point, the concentrations of the acid and its conjugate base are equal. At this point pH = pKa
Henderson–Hassel Balch equation for pH calculation
pH = pKa + [base]/[acid])
So the [base]/[acid]) = 1
The log of 1 = 0
So, the pH = pKa
The equivalence point: At this point neutralization is complete.
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