Subjects

Subjects

More

Search

Download app

Subjects

/

Chemistry

/

Acids and bases

/

Ph and poh of strong acids and bases

/

Ph, poh, strong acids

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

View

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

sheila

@study_withsheila

·

306 Followers

Follow

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

177

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

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.

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

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

Similar Content

Know Acid and Alkalis thumbnail

16

292

10

Acid and Alkalis

acid and alkali book pages + other

Know Molecules thumbnail

7

172

College/11th

Molecules

These notes go over Lewis dot structures, valence electrons, covalent naming, polarity of bonds, electronegativity, molecular geometries, and molecular polarity.

Know Autopyrolysis of Water thumbnail

0

14

Autopyrolysis of Water

This study material contain information on the autopyrolysis of water. Formulas and sample problems are also included.

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

13 M

Students use Knowunity

#1

In Education App Charts in 12 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

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

13 M

Students use Knowunity

#1

In Education App Charts in 12 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

Subjects

/

Chemistry

/

Acids and bases

/

Ph and poh of strong acids and bases

/

Ph, poh, strong acids

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

user profile picture

sheila

@study_withsheila

·

306 Followers

Follow

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

177

 

12/13

 

Chemistry

10

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

Sign up to get unlimited access to thousands of study materials. It's free!

Access to all documents

Join milions of students

Improve your grades

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.

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

Sign up to get unlimited access to thousands of study materials. It's free!

Access to all documents

Join milions of students

Improve your grades

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

Sign up to get unlimited access to thousands of study materials. It's free!

Access to all documents

Join milions of students

Improve your grades

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

Sign up to get unlimited access to thousands of study materials. It's free!

Access to all documents

Join milions of students

Improve your grades

By signing up you accept Terms of Service and Privacy Policy

Similar Content

Chemistry - Acid and Alkalis

acid and alkali book pages + other

16

292

0

Know Acid and Alkalis thumbnail

Chemistry - Molecules

These notes go over Lewis dot structures, valence electrons, covalent naming, polarity of bonds, electronegativity, molecular geometries, and molecular polarity.

7

172

0

Know Molecules thumbnail

Chemistry AP® - Autopyrolysis of Water

This study material contain information on the autopyrolysis of water. Formulas and sample problems are also included.

0

14

0

Know Autopyrolysis of Water thumbnail

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

13 M

Students use Knowunity

#1

In Education App Charts in 12 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