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9/22/2025
Chemistry
Chapter 21.1 - Buffer Solutions
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Sep 22, 2025
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How to Make a Buffer Solution for A Level Chemistry - Easy Guide
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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 (CH3COOH) with a solution of sodium acetate (CH3COONa).
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 (NaOH) to a solution of phosphoric acid (H3PO4).
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 (Ka) 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 (Ka). 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 (CH3COOH)
- 75 cm³ of 1 mol dm⁻³ sodium ethanoate (CH3COONa)
- 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 (HA)
- 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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Brad T
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Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
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Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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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
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This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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 (CH3COOH) with a solution of sodium acetate (CH3COONa).
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 (NaOH) to a solution of phosphoric acid (H3PO4).
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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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 (Ka) 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 (Ka). It's a measure of the strength of an acid in solution.
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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 (CH3COOH)
- 75 cm³ of 1 mol dm⁻³ sodium ethanoate (CH3COONa)
- 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 (HA)
- 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 specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the 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.
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Mock Exam
Quiz
Flashcards
Essay
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user