Subjects

Careers

Open the App

Subjects

How to Make a Buffer Solution for A Level Chemistry - Easy Guide

Open

11

0

user profile picture

sheila

1/2/2023

Chemistry

Chapter 21.1 - Buffer Solutions

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 make a buffer solution, the components of buffer solutions, and methods for calculating the pH of buffer solutions.

  • Buffer solutions minimize pH changes when small amounts of acids or bases are added
  • They consist of a weak acid (HA) and its conjugate base (A-)
  • Two approaches for preparing buffer solutions: mixing weak acid with its salt or partial neutralization
  • pH calculations involve using the acid dissociation constant (Ka) and concentrations of acid and conjugate base
...

1/2/2023

233

21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

View

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 (CH3COOH), the conjugate base is the acetate ion (CH3COO-).

21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

View

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

Rearranging this equation gives:

[H+] = Ka × [HA] / [A-]

Highlight: The value of Ka provides the 'coarse tuning' of the buffer's pH, while the ratio of [HA] to [A-] 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 [HA] = [A-], 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 [HA] = [A-], 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.

21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

View

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

[CH3COOH] = (0.8 × 125) / 200 = 0.5 mol dm⁻³ [CH3COO⁻] = (1 × 75) / 200 = 0.375 mol dm⁻³

Step 2: Use the equation [H+] = Ka × [HA] / [A-]

[H+] = (1.74 × 10⁻⁵ × 0.5) / 0.375 = 2.32 × 10⁻⁵ mol dm⁻³

Step 3: Calculate pH

pH = -log(2.32 × 10⁻⁵) = 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.

Can't find what you're looking for? Explore other subjects.

Knowunity is the # 1 ranked education app in five European countries

Knowunity was a featured story by Apple and has consistently topped the app store charts within the education category in Germany, Italy, Poland, Switzerland and United Kingdom. Join Knowunity today and help millions of students around the world.

Ranked #1 Education App

Download in

Google Play

Download in

App Store

Knowunity is the # 1 ranked education app in five European countries

4.9+

Average App Rating

21 M

Students use Knowunity

#1

In Education App Charts in 17 Countries

950 K+

Students uploaded study notes

Still not sure? Look at what your fellow peers are saying...

iOS User

I love this app so much [...] I recommend Knowunity to everyone!!! I went from a C to an A with it :D

Stefan S, iOS User

The application is very simple and well designed. So far I have found what I was looking for :D

SuSSan, iOS User

Love this App ❤️, I use it basically all the time whenever I'm studying

 

Chemistry

233

Jan 2, 2023

4 pages

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
21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

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

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 (CH3COOH), the conjugate base is the acetate ion (CH3COO-).

21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

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

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

Rearranging this equation gives:

[H+] = Ka × [HA] / [A-]

Highlight: The value of Ka provides the 'coarse tuning' of the buffer's pH, while the ratio of [HA] to [A-] 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 [HA] = [A-], 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 [HA] = [A-], 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.

21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

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

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

[CH3COOH] = (0.8 × 125) / 200 = 0.5 mol dm⁻³ [CH3COO⁻] = (1 × 75) / 200 = 0.375 mol dm⁻³

Step 2: Use the equation [H+] = Ka × [HA] / [A-]

[H+] = (1.74 × 10⁻⁵ × 0.5) / 0.375 = 2.32 × 10⁻⁵ mol dm⁻³

Step 3: Calculate pH

pH = -log(2.32 × 10⁻⁵) = 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.

21.1-Buffer solutions
Key facts:
- buffer solution
a system that
minimises PH
Changes when smau
amounts of an acid/
alkali are added
- buffe

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:

  1. A weak acid (HA)
  2. Its conjugate base (A-)

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:

  1. 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
    • [H+] and pH are restored
  2. When alkali is added:

    • OH- ions are introduced
    • H+ + OH- → H2O reaction occurs
    • [H+] decreases
    • HA dissociates
    • The equilibrium shifts to the right
    • [H+] and pH are restored

Example: In a buffer solution containing acetic acid (CH3COOH) and acetate ion (CH3COO-), adding a small amount of HCl would cause the acetate ions to neutralize the added H+ ions, maintaining the pH.

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