What are the characteristics of buffers?

They have a definite pHThe pH will not change if left alone for long periods of timeThe pH won't change if the solution is dilutedThe pH will only change slightly if a small amount of acid or base is addedThey have a range for which they are the most effective at neutralization

Properties of Buffers

Q: What are buffer solutions?

A buffer (or buffer solution) is a solution whose pH will not change drastically when an acid or base is added.

Chemical Analysis

Chemical Reactions

Chemistry Branches

History of Chemistry

Inorganic Chemistry

Ionic and Molecular Compounds

Kinetics

Making Measurements

Nuclear Chemistry

Organic Chemistry

Physical Chemistry

The Earths Atmosphere

TABLE OF CONTENTS :

TABLE OF CONTENTS

Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken

Jetzt kostenlos anmelden

Nie wieder prokastinieren mit unseren Lernerinnerungen.

Jetzt kostenlos anmelden

Our stomachs contain gastric acid to break down food. This acid can even dissolve steel! How is it that such a potent acid is in our stomachs? Well, our body has a "safety" in place, so our stomach isn't acidic enough to dissolve itself! Stomach cells produce bicarbonate which buffers the acid to prevent it from getting too strong (which we will discuss below).

The buffer keeps the stomach pH stable (which we will also discuss later). This pH is between 1.5-3.5. It keeps stomach acid from getting too acidic, but it also prevents it from getting so basic that it can no longer dissolve food. In this article, we'll be diving into buffers and see about their preparation, their properties, and their applications.

This article is about the properties of buffers.
First, we will cover buffer properties.
Then we'll use the Henderson-Hasselbalch equation to calculate the pH of a buffer solution.
Thereafter, we'll learn about what is happening in a buffer solution.
Next, we'll walk through buffer preparation.
Lastly, we'll cover what makes a good buffer and buffer applications.

pH Measurements and the Properties of Buffers

I talked a lot about buffers and pH, but what are they?

A buffer (or buffer solution) is a solution whose pH will not change drastically when an acid/base is added. The buffer capacity is the amount of acid/base a buffer can absorb before the pH changes significantly.

The pH measures how acidic/basic a solution is. The pH scale ranges begin at 0 (most acidic) and go to 14 (most basic).

Now that we know the basic definitions, let's cover the properties of buffers.

Properties of Buffers

Buffers have an identifying set of characteristics, these are:

A definite pH
pH won't change over time
Dilution won't change pH
A slight pH change if a small amount of acid/base is added
A range where they are the most effective

As mentioned previously, buffers have a buffer capacity, which is the amount of acid/base that can be added until a significant pH change occurs. Typically, we consider this to be a change of 1 unit. (ex. from 3 to 4). A buffer's concentration determines its capacity. As concentration increases, more acid/base can be absorbed until a large change happens.

Properties and Buffers Effect of concentration on buffer capacity StudySmarter Figure 1: Buffer Capacity - the greater the concentration, the greater the buffer capacity. Study Smarter Orginal

As illustrated above, the greater the concentration of the buffer, the greater the capacity. The "spike" in the graph shows where the pH begins to significantly change (buffer isn't as effective). After the spike, it becomes an effective basic buffer.

The buffer range is the range of pH values where a buffer is most effective. The best solutions have a 50:50 ratio of acid to base. Generally, a buffer isn't effective when one component is >10% of the other. For example, a buffer is prepared that has 0.1 M acetic acid (CH₃COOH) and 0.008 M acetate (CH₃COONa). If more base is added, the buffer will be "overwhelmed" and the pH will change significantly.

Properties and Buffers The buffer range of acetic acid StudySmarter Figure 2: Once there is a 10:1 ratio of base to acid, the pH begins to change significantly as more base is added. StudySmarter Original.

As more base is added, the acetic acid converts to acetate. Once there is a 10:1 ratio of acetate to acetic acid (shown by the black dot), the pH starts changing significantly. From the data, we see that the acetic acid buffer loses effectiveness around pH = 6.

pH Measurements and the Henderson-Hasselbalch Equation

We measure a buffer's pH using the Henderson-Hasselbalch equation.

The Henderson-Hasselbalch equation measures a buffer's pH. The formula is: $$pH=pK_a+log_{10}(\frac{[A^-]}{[HA]})$$

pK_a: negative logarithm of the acid dissociation constant (K_a)

[A^-]: concentration of the conjugate base

[HA]: concentration of the acid

The acid dissociation constant measures an acid's strength. A larger constant means a stronger acid. For a general reaction: $$HA+B\leftrightarrow A^-+HB$$

The acid dissociation constant formula is:$$K_a=\frac{[A^-][HB]}{[HA][B]}$$

We measure the pH to see if our buffer is "working". If we add an acid/base, we want to ensure a minimal pH change, or else we would switch buffers.Let's say we have a buffer solution of CH₃COOH (weak acid) and CH₃COONa (conjugate base). Our acid equilibrium looks like:$$CH_3COOH\leftrightarrow CH_3COO^-+H^+$$

When a strong acid is added, its H⁺ ions combine with the CH₃COO^- ions and re-form the weak acid. This "neutralizes" the acid, preventing a large pH change.

What is the pH of the solution if 0.26 mol of CH₃COOH and 0.23 mol of CH₃COONa are combined, with a total volume of 4 L? What is the new pH and change in pH if 0.14 mol of HCl is added, making the total volume 5 L? K_a= 1.75 X 10^-5.

First we calculate the pH. To get the concentration of our acid/base, we divide the number of moles by the total volume for each:

$[CH_3COOH]=[HA]=(0.26\,mol\,4)=0.065\,M$

$[CH_3COONa]=[A^-]=(0.23\,mol/4)=0.0575\,M$

Now we convert from K_a to pK_a:

$pK_a=-log[K_a]$

$pK_a=-log[1.75X10^-5]=4.76$

We plug these values into our main equation:

$pH=pK_a+log_{10}(\frac{[A^-]}{[HA]})$

$pH=4.76+log_{10}(\frac{[0.0575\,mol]}{[0.065\,mol]})$

$pH=4.71$

For the second part of the problem, we must calculate the new concentrations of acid/base. The base concentration is the molar amount divided by the new volume. The acid concentration is equal to moles of weak acid plus moles of strong acid divided by volume.

$[HA]=[HCl]+[CH_3COOH]=(0.26\,mol+0.14\,mol)/5L=0.08\,M$

$[A^-]=[CH_3COONa]=(0.23\,mol/5\,L)=0.046\,M$

We plug these concentrations into the equation:

$pH=pK_a+log_{10}(\frac{[A^-]}{[HA]})$

$pH=4.76+log_{10}(\frac{[0.046\,mol]}{[0.08\,mol]})$

$pH=4.52$

Our change in pH is:

$4.71-4.52=0.19$

Despite a strong acid being added, the pH didn't change much.

Structure and Properties of Water pH Buffers

There are two types of buffers: weak acids + their conjugate base, or weak bases + their conjugate acid. Buffers are aqueous solutions (dissolved in water).

The previous example was a weak acid and its conjugate base. (acetic acid/acetate). We covered what happens when this type has a strong acid added to it, but what about a strong base?

~~$CH_3COOH\leftrightarrow CH_3COO^-+H^+$~~

$CH_3COOH+OH^-\leftrightarrow CH_3COO^-+H_2O$

The base adds OH^- ions which react with the weak acid to produce water, so the pH is unchanged.

Now for weak base/conjugate acid pairs. The main difference between the types is there is a weak base equilibrium, instead of a weak acid one. Let's look at the NH₄OH/NH₄Cl pair as an example. The equilibrium equation is:

$$NH_4OH\leftrightarrow NH_4^+ + OH^-$$

If an acid is added, the H⁺ ions combine with the weak base to form water

$$NH_4OH+H^+\leftrightarrow NH_4^+ +H_2O$$

When a base is added, the OH^- ions will react with the NH₄⁺ ions to form the weak base.

$$NH_4^+ + OH^-\leftrightarrow NH_4OH^+$$

Determination of Appropriate Indicators & Preparation and Properties of Buffers

Now that we've covered how a buffer works, we'll cover how to make and choose a buffer.

Determining an Appropriate Buffer

When choosing a buffer, you want to ensure that it can buffer the system you want. The buffer range should cover the pH you wish to stabilize. Some common buffers are:

Buffer	pK_a	pH range
Phosphoric acid	2.1	1.1-3.1
Formic acid	3.8	2.8-3.8
Acetic acid	4.8	3.8-5.8
Carbonic acid	6.4	5.4-7.4
Phosphate	7.2	6.2-7.2
Bicarbonate	10.3	9.3-11.3

For example, if you want to keep a system neutral (pH=7), you would choose the phosphate buffer (phosphate + phosphoric acid).

Preparing a Buffer Solution

Once you have chosen your buffer, you can prepare the solution. Let's walk through the steps:

Step 1: Use the Henderson-Hasselbalch equation to calculate the acid/base concentration.

Plug in your desired pH and the buffer pK_a into the equation, solving for the ratio of base to acid.

Calculate the ratio of formate to formic acid needed if the buffer is to keep the pH at 3.2. pK_a=3.8.

We plug our values into the Henderson-Hasselbalch equation and solve for the ratio of acid to base.

$pH=pK_a+log_{10}\frac{[A^-]}{[HA]}$

$3.2=3.8+log_{10}\frac{[formate]}{[formic\,acid]}$

$-0.6=log_{10}\frac{[formate]}{[formic\,acid]}$

$10^{-0.6}=\frac{[formate]}{[formic\,acid]}$

$\frac{[formate]}{[formic\,acid]}=0.251$

Step 2: Mix the required amounts of the weak acid/base with its conjugate base/acid.

The conjugate base can be added directly to the acid or a strong base can be added to the weak acid, partially converting it to the conjugate base (the same can be done with a strong acid+weak base)

Continuing from the previous problem, if the buffer needs to be 0.20 M and 100.0 mL, how many grams of formate (CHO₂) and formic acid (CH₂O₂) must be combined?

Firstly, we calculate the total molar amount.

$100.0\,mL*\frac{1\,L}{1000\,mL}=0.1\,L$

$\frac{0.20\,mol}{L}*0.1\,L=0.020\,mol$

This means the sum of the moles of acid/base is equal to 0.020. The ratio of base to acid is 0.251, so we use that to solve for each molar amount.

$[formate]+[formic\,acid]=0.020\,mol$

$\frac{[formate]}{[formic\,acid]}=0.251$

$[formate]=0.251[formic\,acid]$

We substitute this expression into the first equation and solve for the moles of base

$[formate]+[formic\,acid]=0.020\,mol$

$0.251[formic\,acid] +[formic\,acid]=0.020\,mol$

$1.251[formic\,acid]=0.020\,mol$

$[formic\,acid]=0.0160\,mol$

$[formate]+[formic\,acid]=0.020\,mol$

$[formate]+0.0160=0.020\,mol$

$[formate]=0.004\,mol$

Our last step is to convert from moles to grams. We do this by calculating the molar mass of each species and multiplying it by our molar amounts.

Let's start with formic acid (CH₂O₂), first let's calculate its molar mass:

$H:\frac{1.01\,g}{mol}$

$C:\frac{12.01\,g}{mol}$

$O:\frac{16.00\,g}{mol}$

$12.01+2(16.00)+2(1.01)=\frac{46.03\,g}{mol}$

Since formate (CHO₂) is just formic acid minus one hydrogen, we subtract the mass of one hydrogen from formic acid's molar mass to get formate's.

$46.03-1.01=\frac{45.02\,g}{mol}$

Lastly, we multiply the molar amounts by their molar masses to convert to grams.

$0.0160\,mol*\frac{46.03\,g\,CH_2O_2}{mol}=0.736\,g\,CH_2O_2$

$0.004\,mol*\frac{45.02\,g\,CHO_2}{mol}=0.18\,g\,CHO_2$

Step 3 (optional): Adjust the pH.

When experimenting, there may be some error that makes the pH slightly off. Using a pH meter, you can monitor the pH as you add small amounts of strong acid/base to get the desired pH.

Characteristics of a Good Buffer

What makes a buffer "good"?

[HA] = [A^-]. The logarithm in the Henderson-Hasselbalch equation will be equal to zero, so the pH = pK_a. This means the system can equally absorb acids/bases.
If the desired pH is basic, then a weak base + its acid is the most effective. It's the opposite for acids.
The desired pH is within the buffer's range

Buffers want to keep the pH stable, so a "good" buffer is any buffer that can keep a system stable at the desired pH.

Applications of a Buffer Solution

Buffers have several applications. Enzymes must be kept in a specific pH range or else they will degrade\lose usefulness, so the body uses buffers to stabilize the pH. Buffers are also important in manufacturing and industry. They are used during fermentation and during the production of products like inks, dyes, and paper. They are also important for food preservation.

Properties of Buffers - Key takeaways

A buffer (or buffer solution) is a solution whose pH will not change drastically when an acid/base is added. The buffer capacity is the amount of acid/base a buffer can absorb before the pH changes significantly.
The pH measures how acidic/basic a solution is. The pH scale ranges begin at 0 (most acidic) and go to 14 (most basic)
The buffer range is the range of pH values where a buffer is most effective.
Buffers neutralize acids/bases by reacting with them to either form water or the weak acid/base depending on the system.
The Henderson-Hasselbalch equation measures a buffer's pH. The formula is: $$pH=pK_a+log_{10}(\frac{[A^-]}{[HA]})$$
To prepare a buffer, we use the Henderson-Hasselbalch equation to calculate the required ratio of base to acid. The ratio is used to calculate the amount of weak acid/base and its conjugate that needs to be mixed.
Buffers have many applications, such as keeping enzymes stable, manufacturing, and chemical analysis.

Frequently Asked Questions about Properties of Buffers

They have a definite pH
The pH will not change if left alone for long periods of time
The pH won't change if the solution is diluted
The pH will only change slightly if a small amount of acid or base is added
They have a range for which they are the most effective at neutralization

They prevent the pH from changing significantly.

A buffer (or buffer solution) is a solution whose pH will not change drastically when an acid or base is added.

Some examples are: acetic acid/acetate, formic acid/formate, and bicarbonate/carbonic acid.

They have many applications, such as preventing enzymes from breaking down, preserving food, and calibrating pH meters. They are used because of their ability to minimize changes to the pH.

Final Properties of Buffers Quiz

Properties of Buffers Quiz - Teste dein Wissen

Question

What is a buffer?

Show answer

Answer

A buffer (or buffer solution) is a solution whose pH will not change drastically when an acid or base is added.

Show question

Question

What is buffer capacity?

Show answer

Answer

The buffer capacity is the amount of acid or base a buffer can absorb before the pH changes significantly.

Show question

Question

Which of the following is NOT a property of a buffer?

Show answer

Answer

Buffers are liquids

Show question

Question

True or False: An increase in buffer concentration means an increase in buffer capacity

Show answer

Answer

True

Show question

Question

What is the ratio of base to acid where the buffer starts to lose effectiveness?

Show answer

Answer

10:1

Show question

Question

What is the pH of a solution where 0.31 mol of H₃PO₄ and 0.33 mol of H₂PO₄ are combined, with a total volume of 1.5 L? The pK_a of phosphoric acid (H₃PO₄) is 2.1.

Show answer

Answer

2.13

Show question

Question

If a buffer solution is 0.34 mol H₃PO₄ and 0.38 mol H₂PO₄ with a volume of 2.3 L, what is the pH when 0.25 M HCl is added and the new volume is 2.5 L? The pK_a of phosphoric acid (H₃PO₄) is 2.1.

Show answer

Answer

1.70

Show question

Question

Which of the following buffers would be the best for a basic solution?

Show answer

Answer

Bicarbonate/carbonic acid: pH range 9.3-11.3

Show question

Question

What are the steps to preparing a buffer?

Show answer

Answer

Step 1: Use the Henderson-Hasselbach equation to determine the concentration needed for the acid and base.

Step 2: Mix the required amounts of the weak acid/base with its conjugate base/acid.

Step 3 (optional): Adjust the pH if needed.

Show question

Question

Calculate the ratio to bicarbonate to carbonic acid if the buffer system will be used to keep the pH at 10.1. The pKa of bicarbonate is 10.3.

Show answer

Answer

0.631

Show question

Question

If the ratio of H₂PO₄ to H₃PO₄ is 1.23 and the solution needs to be 0.50 M and 200 mL, how many grams of each need to be combined?

Show answer

Answer

5.35 g H₂PO₄

4.39 g H₃PO₄

Show question

Question

What is the ideal ratio of base to acid for a buffer?

Show answer

Answer

1:1

Show question

Question

Which of the following is NOT an application of buffers?

Show answer

Answer

Stabilize the pH of drinking water

Show question

More about Properties of Buffers

Select your language

Properties of Buffers

Properties of Buffers

pH Measurements and the Properties of Buffers

Properties of Buffers

pH Measurements and the Henderson-Hasselbalch Equation

Structure and Properties of Water pH Buffers

Determination of Appropriate Indicators & Preparation and Properties of Buffers

Determining an Appropriate Buffer

Preparing a Buffer Solution

Characteristics of a Good Buffer

Applications of a Buffer Solution

Properties of Buffers - Key takeaways

Frequently Asked Questions about Properties of Buffers

What are the characteristics of buffers?

What is the most important property of a buffer solution?

What are buffer solutions?

What are examples of buffers?

Why are buffers used?

Final Properties of Buffers Quiz

Properties of Buffers Quiz - Teste dein Wissen

More explanations about Physical Chemistry

Discover the right content for your subjects

Biology

Business Studies

Combined Science

Economics

English

English Literature

Environmental Science

Geography

History

Human Geography

Macroeconomics

Marketing

Math

Microeconomics

Physics

Politics

Psychology

Sociology

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Quizzes

Flashcards

Notes

Study Sets

Documents

Study Analytics

Weekly Goals

Smart Reminders

Rewards

Magic Marker

Smart Formatting

Join millions of people in learning anywhere, anytime - every day

This is still free to read, it's not a paywall.

You need to register to keep reading

This is still free to read, it's not a paywall.

You need to register to keep reading

Get FREE ACCESS to all of our study material, tailor-made!

StudySmarter bietet alles, was du für deinen Lernerfolg brauchst - in einer App!