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Chapter 21.1 - Buffer Solutions
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28 Jun 2025
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How to Make a Buffer Solution for A Level Chemistry - Easy Guide
Preparing Buffer Solutions
This section discusses two approaches to prepare buffer solutions in the lab, which is an essential skill for A Level Chemistry students.
Approach 1: Mixing Solutions
The first method involves mixing a solution of a weak acid with a solution containing the salt of the weak acid.
Example: To create an acetate buffer, you might mix a solution of acetic acid with a solution of sodium acetate .
Approach 2: Weak Neutralization
The second method involves adding an aqueous solution of alkali to an excess of a weak acid.
Highlight: In this approach, the weak acid is partially neutralized, resulting in a solution containing both unreacted HA and the A- salt.
Example: To prepare a phosphate buffer, you could add a calculated amount of sodium hydroxide to a solution of phosphoric acid .
Both methods result in a solution containing a weak acid and its conjugate base, which is the essence of a buffer solution.
Vocabulary: Conjugate base - The species formed when an acid donates a proton. In the case of acetic acid , the conjugate base is the acetate ion .
Calculating pH of Buffer Solutions
Understanding how to calculate the pH of buffer solutions is crucial for A Level Chemistry students, particularly when dealing with buffer calculations in AQA A Level Chemistry questions.
The calculation of buffer pH involves the use of the Henderson-Hasselbalch equation, which is derived from the acid dissociation constant expression:
Ka = /
Rearranging this equation gives:
= Ka × /
Highlight: The value of Ka provides the 'coarse tuning' of the buffer's pH, while the ratio of to allows for 'fine tuning'.
Key points to remember:
- The pH of a buffer depends on the Ka value and the ratio of concentrations of HA and A-
- When = , pH = pKa
- For more precise calculations, use the actual concentrations rather than assuming a 1:1 ratio
Example: For a buffer made from a weak acid with pKa = 4.7, if = , the pH would be 4.7.
Vocabulary: pKa - The negative logarithm of the acid dissociation constant . It's a measure of the strength of an acid in solution.
Practical Example: Calculating Buffer pH
This section provides a practical example of how to calculate the pH of a buffer solution, which is a common type of question in A Level Chemistry buffer calculations.
Example: Ethanoic acid buffer
Given:
- 125 cm³ of 0.8 mol dm⁻³ ethanoic acid
- 75 cm³ of 1 mol dm⁻³ sodium ethanoate
- Ka of ethanoic acid = 1.74 × 10⁻⁵ mol dm⁻³
Step 1: Calculate new concentrations after mixing
= / 200 = 0.5 mol dm⁻³ = / 200 = 0.375 mol dm⁻³
Step 2: Use the equation = Ka × /
= / 0.375 = 2.32 × 10⁻⁵ mol dm⁻³
Step 3: Calculate pH
pH = -log = 4.63
Highlight: This example demonstrates how to prepare a buffer solution with a specific pH and how to calculate pH of buffer solution given molarity and volume.
Example: If you needed to prepare a pH 4 buffer solution, you would adjust the ratio of acid to conjugate base to achieve this pH.
Understanding these calculations is crucial for mastering buffers in A Level Chemistry OCR and other exam boards.
Understanding Buffer Solutions
Buffer solutions play a crucial role in maintaining stable pH levels in various chemical and biological systems. This section explores the fundamental concepts of buffer solutions and their mechanisms.
Definition: A buffer solution is a system that minimizes pH changes when small amounts of an acid or alkali are added.
The key components of a buffer solution are:
- A weak acid
- Its conjugate base
Highlight: Buffer solutions require a large reservoir of both HA and A- to effectively resist pH changes.
The mechanism of buffer action can be understood in two scenarios:
- When acid is added: H+ ions are introduced to the solution The large reservoir of A- reacts with excess H+ The equilibrium shifts to the left and pH are restored
- When alkali is added: OH- ions are introduced H+ + OH- → H2O reaction occurs decreases HA dissociates The equilibrium shifts to the right and pH are restored
Example: In a buffer solution containing acetic acid and acetate ion , adding a small amount of HCl would cause the acetate ions to neutralize the added H+ ions, maintaining the pH.
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Samantha Klich
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
How to Make a Buffer Solution for A Level Chemistry - Easy Guide
Buffer solutions are essential in maintaining stable pH levels in various chemical and biological systems. This summary explores the concept of buffer solutions, their preparation, and pH calculations in A Level Chemistry. It covers key aspects of how to... Show more
Preparing Buffer Solutions
This section discusses two approaches to prepare buffer solutions in the lab, which is an essential skill for A Level Chemistry students.
Approach 1: Mixing Solutions
The first method involves mixing a solution of a weak acid with a solution containing the salt of the weak acid.
Example: To create an acetate buffer, you might mix a solution of acetic acid with a solution of sodium acetate .
Approach 2: Weak Neutralization
The second method involves adding an aqueous solution of alkali to an excess of a weak acid.
Highlight: In this approach, the weak acid is partially neutralized, resulting in a solution containing both unreacted HA and the A- salt.
Example: To prepare a phosphate buffer, you could add a calculated amount of sodium hydroxide to a solution of phosphoric acid .
Both methods result in a solution containing a weak acid and its conjugate base, which is the essence of a buffer solution.
Vocabulary: Conjugate base - The species formed when an acid donates a proton. In the case of acetic acid , the conjugate base is the acetate ion .
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Improve your grades
Join milions of students
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Calculating pH of Buffer Solutions
Understanding how to calculate the pH of buffer solutions is crucial for A Level Chemistry students, particularly when dealing with buffer calculations in AQA A Level Chemistry questions.
The calculation of buffer pH involves the use of the Henderson-Hasselbalch equation, which is derived from the acid dissociation constant expression:
Ka = /
Rearranging this equation gives:
= Ka × /
Highlight: The value of Ka provides the 'coarse tuning' of the buffer's pH, while the ratio of to allows for 'fine tuning'.
Key points to remember:
- The pH of a buffer depends on the Ka value and the ratio of concentrations of HA and A-
- When = , pH = pKa
- For more precise calculations, use the actual concentrations rather than assuming a 1:1 ratio
Example: For a buffer made from a weak acid with pKa = 4.7, if = , the pH would be 4.7.
Vocabulary: pKa - The negative logarithm of the acid dissociation constant . It's a measure of the strength of an acid in solution.
Practical Example: Calculating Buffer pH
This section provides a practical example of how to calculate the pH of a buffer solution, which is a common type of question in A Level Chemistry buffer calculations.
Example: Ethanoic acid buffer
Given:
- 125 cm³ of 0.8 mol dm⁻³ ethanoic acid
- 75 cm³ of 1 mol dm⁻³ sodium ethanoate
- Ka of ethanoic acid = 1.74 × 10⁻⁵ mol dm⁻³
Step 1: Calculate new concentrations after mixing
= / 200 = 0.5 mol dm⁻³ = / 200 = 0.375 mol dm⁻³
Step 2: Use the equation = Ka × /
= / 0.375 = 2.32 × 10⁻⁵ mol dm⁻³
Step 3: Calculate pH
pH = -log = 4.63
Highlight: This example demonstrates how to prepare a buffer solution with a specific pH and how to calculate pH of buffer solution given molarity and volume.
Example: If you needed to prepare a pH 4 buffer solution, you would adjust the ratio of acid to conjugate base to achieve this pH.
Understanding these calculations is crucial for mastering buffers in A Level Chemistry OCR and other exam boards.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Understanding Buffer Solutions
Buffer solutions play a crucial role in maintaining stable pH levels in various chemical and biological systems. This section explores the fundamental concepts of buffer solutions and their mechanisms.
Definition: A buffer solution is a system that minimizes pH changes when small amounts of an acid or alkali are added.
The key components of a buffer solution are:
- A weak acid
- Its conjugate base
Highlight: Buffer solutions require a large reservoir of both HA and A- to effectively resist pH changes.
The mechanism of buffer action can be understood in two scenarios:
- When acid is added: H+ ions are introduced to the solution The large reservoir of A- reacts with excess H+ The equilibrium shifts to the left and pH are restored
- When alkali is added: OH- ions are introduced H+ + OH- → H2O reaction occurs decreases HA dissociates The equilibrium shifts to the right and pH are restored
Example: In a buffer solution containing acetic acid and acetate ion , adding a small amount of HCl would cause the acetate ions to neutralize the added H+ ions, maintaining the pH.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user