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8.8 Properties of Buffers

4 min readjanuary 9, 2023

Dylan Black

Dylan Black

Jillian Holbrook

Jillian Holbrook

Dylan Black

Dylan Black

Jillian Holbrook

Jillian Holbrook

In this section, we review what are and how they form, including why we care about in the first place. For chemistry, we often look for solutions with unique properties, whether that be a specific compound, reaction, or observation made. In the case of , these solutions resist changes in pH. This means that adding strong acids or strong bases to them does not impact the pH as much.

It is important to note, however, that are not immune to changes in pH and do have a certain that we will talk about later. 

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-jrHYgH8pXKBj.gif?alt=media&token=b2900019-2e3e-49db-9080-919a1804778d

Get it? Buffering? We're hilarious. Image from GIPHY

Buffers Review

As we mentioned, are special solutions that are resistant to when adding acids or bases to them. are formed in a very specific way: creating a solution of a and its (or a and its , but the former is much more common).

It is important that the acid you create a buffer with is weak because otherwise, the would not be a . For example, a mixture of HCl and NaCl would not be a buffer despite being a combination of an acid (HCl) and its (Cl-).

You may be asking then why any isn't a buffer. At , there is so much more acid than the (assuming a low Ka) that the buffer effects are negligible. In order for a buffer to be effective, you must have comparable concentrations of acid and . In fact, the maximum buffer, the point at which the buffer most effectively resists pH change, occurs when the concentration of acid is equal to the concentration of the .

Solidify this concept by doing a few practice problems. For each of the pairs of compounds given, identify them as a pair that would form a buffer or not form a buffer:

  • NaOH and Na+:

    • The answer to this question is no. Although NaOH and Na+ are a base- pair, remember that NaOH is a . This means that Na+ is not a significant acid and will not form a buffer.

  • CH3COOH and Ca(CH₃COO)₂:

    • The answer to this question is yes! When dissolved together, this pair will form a buffer. CH3COOH is a (acetic acid AKA vinegar) with a Ka=1.8 * 10^(-5). Ca(CH3COO)2 is calcium acetate, which will dissociate into Ca2+ (a as far as the buffer is concerned), and two moles of CH3COO-, the of CH3COOH! Because acetic acid is a , CH3COO- is a , meaning that we will have a buffer.

  • NH3 and NH4NO3:

    • This pair does form a buffer. NH3 is a , and NH4+ is a significant acid (and its ), meaning this pair forms a buffer. In this case, like Ca2+ in the previous example, the nitrate ion is simply a spectator.

  • HI and I:

    • Like example one, this pair does not form a buffer. HI is a and cannot form with its I- because I- is not a .

  • KI and PbNO3:

    • It should be pretty easy to see that this pair does not form a buffer. There are no acids or bases involved. In fact, when you mix KI and PbNO3, you get the "golden rain" reaction, a precipitation reaction that forms PbI2 and KNO3. Take a look!

    https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-FYkiYWIj5KIV.jpg?alt=media&token=9f1cabbf-a0ca-44bc-ad75-d5a135444bd1

Image From ChemTalk

    What Makes Buffers Cool: pH Resistance

    Why do have , and what makes them so interesting and useful to study? have because of the presence of an acid and a base that do not actively react together at . This graphic shows what happens when an acid or a base is added to a buffer:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-nwhcAp4s83sZ.png?alt=media&token=3da51e99-25fa-46ed-9a24-4b99de1ab0a1

Image From LibreTexts

When a is added to a buffer, the eats it up and forms HAn (An = ). In the case of no buffer, the would completely dissociate into H+, increasing [H+] to a much higher degree. Similarly, if OH- from a is added to a buffer, the HAn present in the solution reacts with it to form An- and H2O instead of letting it produce pure OH-. These two reactions lead to being resistant to pH!

Key Terms to Review (16)

Acid Concentration

: Acid concentration refers to the amount of acid present in a solution, usually measured in moles per liter (Molarity).

Anion

: An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.

Base Concentration

: Base concentration refers to the amount of base present in a solution, typically measured as molarity.

Buffer Capacity

: Buffer capacity refers to the amount of acid or base that can be added to a buffer solution before its pH starts to change significantly.

Buffers

: Buffers are solutions that resist changes in their pH when small amounts of an acid or a base are added.

Conjugate Acid

: A conjugate acid is a species formed by the reception of a proton (H+) by a base—in other words, it is the base with a hydrogen ion added to it.

Conjugate Base

: The conjugate base is what remains of an acid after it has donated its proton during an acid-base reaction.

Equilibrium

: Equilibrium refers to the state in which both reactants and products are present in concentrations which have no further tendency to change over time. It's when forward and reverse reactions occur at equal rates so there's no net change observed.

pH Changes

: pH changes refer to shifts in the acidity or alkalinity of a solution, measured on the pH scale ranging from 0 (very acidic) to 14 (very basic).

pH Resistance

: pH resistance refers to how well a solution can resist changes to its pH when small amounts of an acid or base are added.

Significant Base

: In chemistry, there isn't really something called "Significant Base". However, we do have "Strong Base" which refers to bases that completely dissociate into their ions in water.

Spectator Ion

: Spectator ions are ions that exist in the same form on both the reactant and product sides of a chemical equation. They do not participate directly in the reaction.

Strong Acid

: A strong acid is a substance that completely ionizes (breaks down) into its ions in water. This means it donates all of its hydrogen ions (H+) when dissolved in water.

Strong Base

: A strong base is a substance that can completely dissociate in water, producing hydroxide ions (OH-) and the corresponding cations.

Weak Acid

: A weak acid is one that does not completely dissociate into its ions in water, meaning only some of its molecules donate protons when placed in water.

Weak Base

: A weak base is one that does not completely dissociate into its ions in water.

8.8 Properties of Buffers

4 min readjanuary 9, 2023

Dylan Black

Dylan Black

Jillian Holbrook

Jillian Holbrook

Dylan Black

Dylan Black

Jillian Holbrook

Jillian Holbrook

In this section, we review what are and how they form, including why we care about in the first place. For chemistry, we often look for solutions with unique properties, whether that be a specific compound, reaction, or observation made. In the case of , these solutions resist changes in pH. This means that adding strong acids or strong bases to them does not impact the pH as much.

It is important to note, however, that are not immune to changes in pH and do have a certain that we will talk about later. 

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-jrHYgH8pXKBj.gif?alt=media&token=b2900019-2e3e-49db-9080-919a1804778d

Get it? Buffering? We're hilarious. Image from GIPHY

Buffers Review

As we mentioned, are special solutions that are resistant to when adding acids or bases to them. are formed in a very specific way: creating a solution of a and its (or a and its , but the former is much more common).

It is important that the acid you create a buffer with is weak because otherwise, the would not be a . For example, a mixture of HCl and NaCl would not be a buffer despite being a combination of an acid (HCl) and its (Cl-).

You may be asking then why any isn't a buffer. At , there is so much more acid than the (assuming a low Ka) that the buffer effects are negligible. In order for a buffer to be effective, you must have comparable concentrations of acid and . In fact, the maximum buffer, the point at which the buffer most effectively resists pH change, occurs when the concentration of acid is equal to the concentration of the .

Solidify this concept by doing a few practice problems. For each of the pairs of compounds given, identify them as a pair that would form a buffer or not form a buffer:

  • NaOH and Na+:

    • The answer to this question is no. Although NaOH and Na+ are a base- pair, remember that NaOH is a . This means that Na+ is not a significant acid and will not form a buffer.

  • CH3COOH and Ca(CH₃COO)₂:

    • The answer to this question is yes! When dissolved together, this pair will form a buffer. CH3COOH is a (acetic acid AKA vinegar) with a Ka=1.8 * 10^(-5). Ca(CH3COO)2 is calcium acetate, which will dissociate into Ca2+ (a as far as the buffer is concerned), and two moles of CH3COO-, the of CH3COOH! Because acetic acid is a , CH3COO- is a , meaning that we will have a buffer.

  • NH3 and NH4NO3:

    • This pair does form a buffer. NH3 is a , and NH4+ is a significant acid (and its ), meaning this pair forms a buffer. In this case, like Ca2+ in the previous example, the nitrate ion is simply a spectator.

  • HI and I:

    • Like example one, this pair does not form a buffer. HI is a and cannot form with its I- because I- is not a .

  • KI and PbNO3:

    • It should be pretty easy to see that this pair does not form a buffer. There are no acids or bases involved. In fact, when you mix KI and PbNO3, you get the "golden rain" reaction, a precipitation reaction that forms PbI2 and KNO3. Take a look!

    https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-FYkiYWIj5KIV.jpg?alt=media&token=9f1cabbf-a0ca-44bc-ad75-d5a135444bd1

Image From ChemTalk

    What Makes Buffers Cool: pH Resistance

    Why do have , and what makes them so interesting and useful to study? have because of the presence of an acid and a base that do not actively react together at . This graphic shows what happens when an acid or a base is added to a buffer:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-nwhcAp4s83sZ.png?alt=media&token=3da51e99-25fa-46ed-9a24-4b99de1ab0a1

Image From LibreTexts

When a is added to a buffer, the eats it up and forms HAn (An = ). In the case of no buffer, the would completely dissociate into H+, increasing [H+] to a much higher degree. Similarly, if OH- from a is added to a buffer, the HAn present in the solution reacts with it to form An- and H2O instead of letting it produce pure OH-. These two reactions lead to being resistant to pH!

Key Terms to Review (16)

Acid Concentration

: Acid concentration refers to the amount of acid present in a solution, usually measured in moles per liter (Molarity).

Anion

: An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.

Base Concentration

: Base concentration refers to the amount of base present in a solution, typically measured as molarity.

Buffer Capacity

: Buffer capacity refers to the amount of acid or base that can be added to a buffer solution before its pH starts to change significantly.

Buffers

: Buffers are solutions that resist changes in their pH when small amounts of an acid or a base are added.

Conjugate Acid

: A conjugate acid is a species formed by the reception of a proton (H+) by a base—in other words, it is the base with a hydrogen ion added to it.

Conjugate Base

: The conjugate base is what remains of an acid after it has donated its proton during an acid-base reaction.

Equilibrium

: Equilibrium refers to the state in which both reactants and products are present in concentrations which have no further tendency to change over time. It's when forward and reverse reactions occur at equal rates so there's no net change observed.

pH Changes

: pH changes refer to shifts in the acidity or alkalinity of a solution, measured on the pH scale ranging from 0 (very acidic) to 14 (very basic).

pH Resistance

: pH resistance refers to how well a solution can resist changes to its pH when small amounts of an acid or base are added.

Significant Base

: In chemistry, there isn't really something called "Significant Base". However, we do have "Strong Base" which refers to bases that completely dissociate into their ions in water.

Spectator Ion

: Spectator ions are ions that exist in the same form on both the reactant and product sides of a chemical equation. They do not participate directly in the reaction.

Strong Acid

: A strong acid is a substance that completely ionizes (breaks down) into its ions in water. This means it donates all of its hydrogen ions (H+) when dissolved in water.

Strong Base

: A strong base is a substance that can completely dissociate in water, producing hydroxide ions (OH-) and the corresponding cations.

Weak Acid

: A weak acid is one that does not completely dissociate into its ions in water, meaning only some of its molecules donate protons when placed in water.

Weak Base

: A weak base is one that does not completely dissociate into its ions in water.


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© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.