1- Which of the curves seems to have the most vertical line around the equivalen

Question

1- Which of the curves seems to have the most vertical line around the equivalence point? Explain why. (If you suspect that your data are inaccurate, explain which one you think should have been most vertical and why.)

2-Which of the curves seems to have the most sloping line around its equivalence point? Explain why. (If you suspect that your data are inaccurate, explain which one you think should have been most vertical and why.)

3-State the pH at the equivalence point for each of your four curves.

4-Write the equilibrium equations for each of the four titrations at their equivalence points. You may simply write the net ionic equations.

5-Is the pH at the equivalence point neutral for all of them? Explain why or why not for each of the four.

6-Which of the four systems formed a buffer (at least initially)? Explain why.

Explanation / Answer

1. Most vertical line at equivalence point is for strong acid vs strong base. The line is vertical, because there is sharp increase in pH after neutralization. As acid is strong, so pH is quite low, the acid is fully dissociated. After neutralisation, the pH is due to strong base which is also completely dissociated.

2. Most slopy line is for weak acid vs weak base. Both the acid and base are partially dissociated. So, pH is not defined. Ebven after neutralisation, pH is defined by base which is also very weak. So, the change is not sharp.

3. pH at equivalence point of strong acid vs strong base: 7

pH at equivalence point of weak acid vs strong base: 9

pH at equivalence point of weak acid vs weak base: 8

pH at equivalence point of strong acid vs strong base: 6

4. Net ionic equation for strong acid vs strong base:

H+(aq) + OH- (aq) --------> H2O (l)

Net ionic equation for weak acid vs strong base:

CH3COOH (l) + OH- (aq) ------> CH3COO-(aq) + H2O(l)

Net ionic equation for weak acid vs weak base:

CH3COOH (l) + NH3 (l) ------> CH3COONH4(l)

Net ionic equation for strong acid vs weak base:

H+(aq) + NH3 (l)--------> NH4+(aq)

5. pH is not neutral for all of them. For strong acid vs strong base, it is neutral, because in net ionic equations, water is formed, which is neutral.

In case of weak acid vs strong base, pH is determined by base after neutralisation, so pH is towards basic. In net ionic equation CH3COO- is formed, which is conjugate base of weak acid, thus pH is determined by conjugate base and pH is towards basic.

In case of weak acid vs weak base, salt is being formed, thus pH is 8, almost neutral.

In case of strong acid vs weak base, NH4+ is formed, which is strong conjugate acid of weak base, thus pH is around 6.

6. Buffer is formed by in case of titration of weak acid vs strong base and strong acid vs weak base. In case of weak acid vs strong base, CH3COO- is formed, which is a strong conjugate base of weak acid. Thus, after this even if we add more of NaOH, pH does not get affected, thus it acts as buffer. Similarly, in strong acid vs weak base, NH4+ is formed, which is strong conjugate acid of weak base. After this, addition of H2SO4 will not affect the pH of solution.

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