Compare and contrast the titration curves. Specifically explain how and why the

Question

Compare and contrast the titration curves. Specifically explain how and why the concentration of the acid affects the pH of the solution prior to the equivalence point when the acid is strong, but not when the acid is weak. Discuss why equivalence points occur at the same volume of titrant in all cases and why the curves are the same after the equivalence point.

14 12 10 F HC1-NaOH 0.1 000M 0.01 000M 0.001000 M 20 A0 60 80 Milliliters of strong base added 100 FIGURE 11-1 (a) Curves for the titration of 50.00 ml of hydrochloric acid with a strong base [concen- trations as in Fig. 11-1 (b)]. 1A 12 10 FIGURE 11-1 (b) Curves for the titration of 50.00 ml of acetic acid with a a strong base concentrations 6 as in Fig. 11-7 (a)]. H0Ac NaOH 0.1000 M 0.01 000M 0,00 1000 M 40 80 60 20 Milliliters of strong base added 100

Explanation / Answer

We are comparing strong acid/weak acid with strong base titration curves.

First we will start with strong acid HCl.

a)

We can see three distinct graphs of three molarities viz.0.001M, 0.01 M and 0.1 M.

As the HCl dissociates completely in the water. Since pH is directly proportional to concentration. Therefore, we can see so much gap in three lines.

pH = - log [H+]

As HCl dissociates completely, 0.1 M HCl gives 0.1M H+.

pH =-log [0.1] = 1

Same in all other cases

pH =-log [0.01] = 2

pH =-log [0.001] = 3

In case of, acetic acid, which is weak one. It does not dissociate completely. Thereby having very little effect on pH of solution.

In calculation of pH of weak acid we need to know pKa of acid. It is 4.76 for acetic acid.

pKa = -log[H+] + 2*pH

4.76 = -log[0.1] + 2*pH

4.76+1=2*pH

5.76/2 = pH

pH = 2.88

Same in all other cases.

4.76 = -log[0.01] + 2*pH

4.76+2=2*pH

6.76/2 = pH

pH = 3.38

and

4.76 = -log[0.001] + 2*pH

4.76+3=2*pH

7.76/2 = pH

pH = 3.88

b)

After the equivalence point all the graphs are same because the main differentiating factor was strength of acid and all the acid is neutralized after equivalence point. pH/strength plays the important role in this point. Therefore, after equivalence point graphs are same.

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.