-
Finished your HSC? Check out our University Discussion, Non-School forums or help out next year's HSC students! -
YOU can help the next generation of students in the community! Share your trial papers and notes on our Notes & Resources page
Why does acid strength not matter in neutralisation reactions and the volume required to neutralise is same for a weak strong acid (1 Viewer)
- Thread starter SCREW L+S
- Start date
Eagle Mum
Well-Known Member
- Joined
- Nov 9, 2020
- Messages
- 551
- Gender
- Female
- HSC
- N/A
Your question is in two parts and neither makes sense as they are currently worded.
To try to help, let’s first clarify some definitions:
The concentration of an acid or base is the amount of acid/base in a given amount of solution. A concentrated solution is one that contains a large amount of acid or base in a given volume. A dilute solution is one that contains a small amount of acid or base in a given volume.
The strength of an acid or base describes how much of the acid/base dissociates in solution.
A strong acid essentially dissociates completely in solutions, whilst a weak acid only partially dissociates in solution.
When titrating a strong acid and a strong base, hydronium (H+) and hydroxide (OH-) ions will react to form water, leading to an equivalence point at a pH of 7. Since a strong acid and a strong base will completely dissociate and react with each other to form water at neutral pH 7, to determine the concentration of an unknown strong acid/base, we can take a specific volume of it and slowly add a strong base/acid of known concentration until the solution reaches neutral pH. By measuring the added volume and knowing the concentration of the known solution (titrant), as well as predetermining the volume of the unknown acid/base, we can calculate the concentration of the unknown acid/base.
When a weak acid is titrated with a strong base, the equivalence point is at a pH > 7 and when a strong acid is titrated with a weak base, the equivalence point is at a pH < 7, so the strength of the acid or base does affect the equivalence point of the titration curve which is contrary to your first statement.
WRT to your second statement, ‘a weak strong acid’ is an oxymoron. ‘Weak’ & ‘strong’ are on opposite ends of the spectrum of acid strengths. I am guessing that what you are asking is why the volume (of the same concentration of the same strong base) required to ’neutralise’ a weak or strong acid (of the same concentrations and stoichiometric ratios of reaction with the base) is the same. The answer is that at equivalence point, all of the weak or strong acid has completely reacted with the base with only concentrations and volumes of the solutions being relevant to how much base was required to reach equivalence point. As explained above, there is however a difference between the two scenarios - when the strong base reacts with the weak acid, the conjugate base of the weak acid is formed, so the pH at equivalence point is basic, whereas the reaction product of the strong base & strong acid is water, so pH is neutral at the equivalence point.
To try to help, let’s first clarify some definitions:
The concentration of an acid or base is the amount of acid/base in a given amount of solution. A concentrated solution is one that contains a large amount of acid or base in a given volume. A dilute solution is one that contains a small amount of acid or base in a given volume.
The strength of an acid or base describes how much of the acid/base dissociates in solution.
A strong acid essentially dissociates completely in solutions, whilst a weak acid only partially dissociates in solution.
When titrating a strong acid and a strong base, hydronium (H+) and hydroxide (OH-) ions will react to form water, leading to an equivalence point at a pH of 7. Since a strong acid and a strong base will completely dissociate and react with each other to form water at neutral pH 7, to determine the concentration of an unknown strong acid/base, we can take a specific volume of it and slowly add a strong base/acid of known concentration until the solution reaches neutral pH. By measuring the added volume and knowing the concentration of the known solution (titrant), as well as predetermining the volume of the unknown acid/base, we can calculate the concentration of the unknown acid/base.
When a weak acid is titrated with a strong base, the equivalence point is at a pH > 7 and when a strong acid is titrated with a weak base, the equivalence point is at a pH < 7, so the strength of the acid or base does affect the equivalence point of the titration curve which is contrary to your first statement.
WRT to your second statement, ‘a weak strong acid’ is an oxymoron. ‘Weak’ & ‘strong’ are on opposite ends of the spectrum of acid strengths. I am guessing that what you are asking is why the volume (of the same concentration of the same strong base) required to ’neutralise’ a weak or strong acid (of the same concentrations and stoichiometric ratios of reaction with the base) is the same. The answer is that at equivalence point, all of the weak or strong acid has completely reacted with the base with only concentrations and volumes of the solutions being relevant to how much base was required to reach equivalence point. As explained above, there is however a difference between the two scenarios - when the strong base reacts with the weak acid, the conjugate base of the weak acid is formed, so the pH at equivalence point is basic, whereas the reaction product of the strong base & strong acid is water, so pH is neutral at the equivalence point.
Eagle Mum
Well-Known Member
- Joined
- Nov 9, 2020
- Messages
- 551
- Gender
- Female
- HSC
- N/A
I think the short answer you were looking for is that at equivalence point, all of the weak or strong acid has completely reacted with the base with only concentrations and volumes of the solutions being relevant to how much base was required to reach equivalence point. It took a while to work out what you were asking from the wording of your question.