# Titration Curves for the Dilution of Ethanoic Acid

I am really having trouble answering these titration curve questions. I have not been taught how titration curves differ, i.e. strong acid-weak base, weak acid-strong base etc, but have been researching this by myself.
For part 1; I am very confused how I should plot the titration curve for a solution that is 0.0001 M, from the point where no base has been added, up to the point where 1 mole of OH- has been added on the graph attached. I am very eager to understand this topic fully and want to learn, I am just struggling a little as I have not encountered questions concerning the effect of dilution on the degree of dissociation of a weak acid.
I do understand for a weak acid-strong base curve to begin with there are only H+ ions present in solution from the dissociation of CH3COOH.
However, as the volume of the alkali added increases, the pH of the ethanoic acid solution slightly increases as more H+ ions react with the OH- to form water. Therefore, the change in pH is not too great until the volume added nears the equivalence point, the vertical section at which all H+ ions have been neutralised by the OH- ions.
For a diluted 0.0001 mol dm^-3 solution I believe using the data in the table the curve will begin at a pH of 4.2 instead of ~2.7. Beyond this I do not know how to plot the curve using the information I have been given.
For part 2 I have faced a similar problem in plotting the curve for HOCl on the same diagram.
I would be very grateful for any help that anyone can provide, in as great detail as possible so that I am able to understand this question. Thank you in advance 👍

1. Use the values for the measured pH (from the table attached) to sketch the titration curve for a solution that is 0.0001 M, from the point where no base has been added, up to the point where 1 mole of OH- has been added. Show the initial pH and the pH where the mole equivalent of OH- added is 0.5 and include all of your calculations.

2. A student conducts the the same titration but uses chloric (I) acid HOCl. The acid dissociation constant =
3.2 × 10^–8. Calculate the pH when half of this is neutralised by sodium hydroxide, sketch the pH curve for this titration on the same diagram. Comment on the feasibility of this titration.

3. The equivalence point of the ethanoic acid titration, pH = 8.7. The ionic product of water KW =
1.0 × 10^–14 mol^2 dm^–6. Calculate the hydroxide ion concentration at the equivalence point.
(edited 1 year ago)
Original post by LukeWatson4590
I am really having trouble answering these titration curve questions. I have not been taught how titration curves differ, i.e. strong acid-weak base, weak acid-strong base etc, but have been researching this by myself.
For part 1; I am very confused how I should plot the titration curve for a solution that is 0.0001 M, from the point where no base has been added, up to the point where 1 mole of OH- has been added on the graph attached. I am very eager to understand this topic fully and want to learn, I am just struggling a little as I have not encountered questions concerning the effect of dilution on the degree of dissociation of a weak acid.
I do understand for a weak acid-strong base curve to begin with there are only H+ ions present in solution from the dissociation of CH3COOH.
However, as the volume of the alkali added increases, the pH of the ethanoic acid solution slightly increases as more H+ ions react with the OH- to form water. Therefore, the change in pH is not too great until the volume added nears the equivalence point, the vertical section at which all H+ ions have been neutralised by the OH- ions.
For a diluted 0.0001 mol dm^-3 solution I believe using the data in the table the curve will begin at a pH of 4.2 instead of ~2.7. Beyond this I do not know how to plot the curve using the information I have been given.
For part 2 I have faced a similar problem in plotting the curve for HOCl on the same diagram.
I would be very grateful for any help that anyone can provide, in as great detail as possible so that I am able to understand this question. Thank you in advance 👍

1. Use the values for the measured pH (from the table attached) to sketch the titration curve for a solution that is 0.0001 M, from the point where no base has been added, up to the point where 1 mole of OH- has been added. Show the initial pH and the pH where the mole equivalent of OH- added is 0.5 and include all of your calculations.

2. A student conducts the the same titration but uses chloric (I) acid HOCl. The acid dissociation constant =
3.2 × 10^–8. Calculate the pH when half of this is neutralised by sodium hydroxide, sketch the pH curve for this titration on the same diagram. Comment on the feasibility of this titration.

3. The equivalence point of the ethanoic acid titration, pH = 8.7. The ionic product of water KW =
1.0 × 10^–14 mol^2 dm^–6. Calculate the hydroxide ion concentration at the equivalence point.

Do you know how to determine the pH of buffer solutions?
Would I use pH = pKa + log10([A-]/[HA])?

pKa=acid dissociation constant of the weak acid
[A-]=is the concentration of conjugate base
[HA]=is the concentration of weak acid
Original post by charco
Do you know how to determine the pH of buffer solutions?
Original post by LukeWatson4590
Would I use pH = pKa + log10([A-]/[HA])?

pKa=acid dissociation constant of the weak acid
[A-]=is the concentration of conjugate base
[HA]=is the concentration of weak acid

You could, but I would use

ka = [H+][A-]/[HA]

therefore

[H+] = ka * [HA]/[A-]

and pH = -log10[H+]

-----------------------------------

So its a matter of determining the concentrations of [HA] and [A-] after each addition of base.

Personally, I would set it up in Excel to do all of the calculations automatically.