Intro to Buffers - Online Tutor, Practice Problems & Exam Prep

Buffers are solutions that maintain pH stability by neutralizing added acids or bases, containing both a weak acid and its conjugate base, or vice versa. Ideal buffers have equal concentrations of these components, maximizing resistance to pH changes. Buffer capacity refers to the amount of acid or base a buffer can neutralize without significant pH alteration, with higher concentrations enhancing capacity. The buffer range is determined by the concentration ratio of the weak species to its conjugate, remaining effective within a 10:1 to 1:10 ratio. Deviations from this range reduce buffer effectiveness, highlighting the importance of maintaining the correct concentration ratios for optimal buffering action.

Acid-Base Buffers

ACID base buffers are solutions that resist drastic changes in pH by neutralizing additional acid or base that might be added to it. Here we're going to say that a buffer itself contains both acid and base, and because of that it neutralizes any additional hydroxide ion or hydronium ions that are added respectively.

If we take a look here in this far left image here this beaker represents our buffer solution. Our buffer is composed of hydrofluoric acid and its conjugate base in the form of sodium fluoride. Here the PA. The buffer has a pH around 8.00. What I can do to it is I start adding acid or base if I start adding hydrobromic acid. Hydrobromic acid represents a strong acid. Remember, in terms of neutralization reactions, what is the chemical opposite of this hydrobromic acid? The opposite would be the sodium fluoride, the conjugate base.

So as we add hydrobromic acid to the solution, the fluoride ion, which is basic, would interact with the hydronium ion of hydrofluoric acid. They would bind together and as a result create hydrofluoric acid as well. Within the solution, we're creating acid. And then we're going to say here that the bromide ion and the sodium ion would still be at present as well. But there are spectator ions because they're neutral ions, right? So as I add strong acid, my buffer is slowly neutralizing it. My conjugate base is slowly neutralizing it. Neutralizing it does create some acid.

This causes my pH to drop, but because it's a buffer, the pH is not going to drop by much. So here this would be 7.8 as an example. So drop by, but not by much because we're assuming we're not adding too much of the strong acid. But let's say we added strong base. What would happen there? Well, if I had strong base, it's chemical opposite is an acid, so the hydrofluoric acid of the buffer would interact with that strong base being added.

Here we'd say that the hydroxide ion of the strong base and the hydronium ion of the hydrofluoric acid would interact. They would neutralize each other and we create water. Then we'd say that we have sodium ions that are free floating now and we'd have more fluoride ion freed up, so they'd be floating around. Fluoride ion is a basic ion, so it will cause my solution to become a little bit more basic. As a result, our pH maybe it goes up 8.2.

Again, I'm just showing you that the addition of a strong acid or strong base does change the pH, but it's not going to change it by much because the whole point of a buffer is to resist large changes in your pH as long as not a lot of strong acid or strong base is added.

Buffer Creation

At this point, we know that a buffer contains both an acid and a base. But let's be a little bit more specific here. We're going to say when it comes to buffer creation, there are three ways to create a buffer. Now, the first way to make a buffer is to have either a weak acid or base with its conjugate O. For example, here we have 0.40 molar of ammonia and 0.40 molar of ammonium ion. We can look at this two different ways. We could say that an H3 represents a weak base and the ammonium ion represents its conjugate acid. Or we could say that ammonium ion represents a weak acid because it's a positive amine and ammonia represents its conjugate base. Whichever way you look at it, you're technically correct, right?

So the 1st way to make a buffer is to have a weak acid or base with its conjugate, now an ideal buffer. Which is the best type of buffer? This is the one that makes the most resistance to changes in pH. This happens when your weak acid or base is equal in concentration to its conjugate. So here we have 0.40 of both of these compounds and ions. This will be an ideal buffer.

Now the next two ways, The 2nd way to make a buffer is to have a strong acid with a weak base. Here we'd say that the weak base needs to be greater or higher in concentration. OK, so we have something strong versus something weak. The weak species needs to be greater in amount. So for example, here we have 0.20 molar of hydrochloric acid, which is a strong acid. And then here we have methylamine. It's a neutral amine, so it represents a weak base. For us to have a successful buffer, the weak base must be higher in amount than the strong acid. So here let me put 0.30 molar. Here the weak base is greater in amount, so this could create a buffer.

Now the final way to make a buffer is to have the opposite. Now my base is strong and my acid is weak. But again the weak species. In this case the weak acid, needs to be higher in concentration or higher in amount. Here we have 1.3 molar of potassium amide which is a strong base and here we have sulfurous acid. Here sulfurous acid represents a weak diprotic acid. Again, you want to make sure that your weak species, in this case the weak acid, is greater in amount to ensure the creation of a buffer. So here let me put 2 molar. Also furious acid, right?

So just remember, a buffer is an acid and base together and these are the three specific ways to make any type of buffer.

Intro to Buffers Example

Select all pair or pairs that could form a buffer solution. Remember, a buffer has a acid and a base, but there are three specific ways to make a buffer. One way to make a buffer is to have a weak acid plus its conjugate base or a conjugate acid plus its weak base.

2nd way to make it is to have a strong acid with a weak base. But in this instance, because it's strong and weak, the weak species needs to be greater in amount, greater in concentration and then finally the last way to make one is to have a weak acid and a strong base. Again, the weak species needs to be greater in amount, so we take a look here.

In the first one we have acetic acid. This is a weak acid and hydrophoric acid, which is another weak acid. The only time a weak acid could help make a buffer is if that weak acid is with its conjugate base. Neither one of them is a conjugate of each other. Also, we could have a weak acid with a strong base. Yes, we have weak acids, but where's the strong base?

Next, we have nitric acid and ammonia. Nitric acid represents a strong acid. Ammonia represents a weak. Here strong acid, weak base is one of the three combinations. We're not talking about the amount of each, but we're assuming that the weak species is greater in amount. Therefore a buffer would be created. So this is an answer.

Next we have hydrochloric acid, which is a strong acid. Sodium chloride has one less hydrogen than hydrochloric acid, so this is the conjugate base of the strong acid. Now this does not mean it's a buffer because remember, it's a weak acid plus its conjugate base, not a strong acid and its conjugate base.

Next we have potassium hydroxide, which is a strong base with hydrocyanic acid, which is a weak acid. Again, this is one of the combinations that could create a buffer. So this is an answer.

Then finally we have sodium bromide and sodium hydroxide. Well, sodium bromide here is a strong base and the only way a strong base could help make a buffer is it linked up with a weak acid. And ABR is basically a neutral ionic salt, it's not even a weak acid so this could not work. So out of my choices, option B&D would be the pairs that could form a buffer solution.

Which pairs of compounds are capable of making a buffer? Select all that apply.

a) 1.3 M LiOH and 1.7 M HCOOH                        c) 0.35 M CH₃CO₂H and 0.35 M NaOH

b) 0.784 M NH₄⁺ and 0.800 M HClO₄                  d) 0.80 HNO₃ and 0.15 MgO

• A. 1.3 M LiOH and 1.7 M HCOOH
• B. 0.784 M NH₄⁺ and 0.800 M HClO₄
• C. 0.35 M CH₃CO₂H and 0.35 M NaOH
• D. 0.80 HNO₃ and 0.15 MgO

Buffer Capacity

When we refer to buffer capacity, it's just the amount of acid or base that a buffer can neutralize before the pH of the solution starts to noticeably change. Here we're going to say the larger the concentration of buffer components, then the greater the buffer capacity and we're going to say higher concentration of weak acid and conjugate base.

Remember, this is the most common pair for buffer equals better buffer, right? So basically we want more amounts of the base and acid components of a buffer so that it can more effectively neutralize any additional acid or base added to it.

Intro to Buffers Example

Which of the following combinations would make a buffer with the greatest buffering capacity? Here we're dealing with one liter of solution. If we take a look in options A to D, we have different mole amounts of weak acid and conjugate base for both A&B. We're dealing with chlorous acid, which is a weak acid and we're dealing with sodium chloride, it's conjugate base for C&D. We're dealing with nitrous acid and potassium nitrite.

If we take a look here, if we compare A&B to one another, we have 0.25 moles versus 0.35 moles for our weak acids, 0.20 moles of our conjugate base, 0.25 moles of our conjugate base. B has higher values for weak acid and conjugate base, so it have a greater buffering capacity, so B would be better than A.

If we look at C, C also has weak acid and conjugate base and the mole amounts are even larger. So option C will be better than option B. And then finally, if we're comparing C&D, we have 35 moles versus 50 moles, 30 moles versus 48 moles. Option D will be the better answer since our weak acid and conjugate base have higher values, therefore giving them the greater buffering capacity.

So here our final answer for this question will be option D.

Buffer Range

When taking into consideration a buffer, we must also look at buffer range. Here we're going to say that a buffer is effective as long as it has the right concentration ratio of weak species to its conjugate. Here for buffer range, where we have a ratio of weak acid to conjugate base, it is effective if that ratio is a 1250 ratio or a one to 10 ratio.

Basically at max, one of them can only be 10 times more than the other in terms of amount. If it goes beyond that range, it's no longer going to be an effective buffer. Here we're going to say a buffer is ideal or most effective when the concentration or amount of weak acid is equal to the amount of conjugate base.

Here we're going to say the larger the difference in concentrations between weak species and its conjugate, then the less effective a buffer will be. So again, you always want to play around with that 1250 ratio or one to 10 ratio when comparing your weak acid to its conjugate so to make sure that it will be as effective as possible.

Intro to Buffers Example

Which of the following combinations would create the most effective buffer? So remember with a buffer we talk about buffer range. A buffer is effective as long as the ratio between weak acid and conjugate base is a 12:50 or 1:00 to 10:00 ratio. And we know that the most effective or ideal buffer is when the amount of weak acid is equal to the amount of conjugate base. So weak acid to conjugate base. If you get equal to one, that's the best type of buffer.

So what we're going to do here is we're going to figure out what the ratio is for each of the weak acid conjugate base pairs. The one that has a ratio closest to one would be most ideal and therefore most effective buffer. So if we take a look here in all of these examples, what do we have? Well, we have here is methyl ammonium ion. It is a positively charged amine, which remember positively charged amines are weak acids and then methylamine is just its version with one less H. So this would be the conjugate base.

All we're going to do here is we're going to take the ratios of each of them and see which one comes closest to one that would represent the most ideal buffer. So for A, the ratio of weak acid to conjugate base equals 1.01.2, which comes out to 0.83. For B, what do we have? We have weak acid 0.78 divided by conjugate base 1.3, so this comes out to 0.60. For C, we have 1.5 molar of our weak acid divided by 0.25 molar. So this comes out to 6 and then D, we have 6.8 molar of our weak acid divided by 0.68 molar of our conjugate base. This comes out to 10.

Based on these ratios, the one closest to one is option A. Option A will represent the pairing that is the most ideal buffer and therefore the most effective buffer. Now if they ask us the opposite, which of these options would be the least effective buffer? We'd say option D because option D we have such a vast difference in their concentrations. It's right on the edge of our buffer range, right? So keep in mind for this particular one the answer is option A.

Determine which of the following actions will destroy a buffer composed of 0.50 L of 1.44 M H₃PO₄ and 0.60 L of 1.25 M NaH₂PO₄⁻.

a) Addition of 1.45 moles of KH₂PO₄

b) Addition of 0.85 moles of HCl

c) Addition of water

d) Addition of 0.30 moles of Ca(OH)₂

e) Addition of 0.70 moles of HIO₄

• A. Addition of 1.45 moles of KH₂PO₄
• B. Addition of 0.85 moles of HCl
• C. Addition of water
• D. Addition of 0.30 moles of Ca(OH)₂
• E. Addition of 0.70 moles of HIO₄

Here’s what students ask on this topic:

What are buffers?

Buffers are substances that help maintain and stabilize the pH levels of a solution by neutralizing small amounts of added acid or base. They are typically made up of a weak acid and its conjugate base or a weak base and its conjugate acid. When an acid (proton donor) is added to the solution, the buffer's base component will react with it to minimize the change in pH. Conversely, when a base (proton acceptor) is added, the acid component of the buffer will react to neutralize the base.

This ability to maintain pH is crucial in many biological systems where enzymes and other biochemical processes are highly sensitive to changes in acidity. For example, blood in the human body has a buffering system involving carbonic acid and bicarbonate to maintain pH within a narrow range, ensuring proper physiological function. In chemical applications, buffers are used in processes and reactions that require a constant pH.

How do buffers work?

Buffers are solutions that resist changes in pH when acids or bases are added to them. They work through a system of a weak acid and its conjugate base or a weak base and its conjugate acid. When an acid ($H^{+}$ ions) is added to a buffer, the conjugate base present in the buffer solution will react with the $H^{+}$ ions to form the weak acid, minimizing the change in pH. Conversely, when a base (${\mathrm{OH}}^{-}$ ions) is added, the weak acid in the buffer donates $H^{+}$ ions to neutralize the ${\mathrm{OH}}^{-}$ ions, forming water and the conjugate base, again preventing a significant shift in pH.

This balance is described by the Henderson-Hasselbalch equation, which relates pH to the pKa (acid dissociation constant) of the weak acid and the ratio of the concentrations of the conjugate base to the weak acid. Buffers are essential in biological systems and chemical reactions where maintaining a stable pH is critical for proper functioning or reaction outcomes.

How do buffers moderate pH change?

Buffers moderate pH change by absorbing excess hydrogen ions (H⁺) or hydroxide ions (OH^-) that are introduced into a solution. A buffer typically consists of a weak acid and its conjugate base, or a weak base and its conjugate acid. When the pH of a solution begins to drop because of the addition of H⁺, the weak base component of the buffer will react with the H⁺ to form the weak acid, thereby removing the excess H⁺ from the solution and minimizing the change in pH. Conversely, if the pH begins to rise due to the addition of OH^-, the weak acid component of the buffer will donate H⁺ to neutralize the OH^-, forming water and the conjugate base, again preventing a significant shift in pH. This ability to maintain a stable pH is crucial for many biological and chemical processes where the function of molecules is highly sensitive to the pH of the environment.

How do buffers resist changes in pH?

Buffers resist changes in pH by using a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid. When an acid (H⁺ ions) is added to a solution with a buffer, the conjugate base present in the buffer will react with the added H⁺ ions to form the weak acid, thus minimizing the increase in the hydrogen ion concentration and preventing a significant drop in pH. Conversely, when a base (OH^- ions) is added, the weak acid component of the buffer donates H⁺ ions to neutralize the OH^- ions, forming water and the conjugate base. This reaction reduces the amount of OH^- ions, preventing a significant rise in pH. Essentially, buffers work by absorbing excess H⁺ or OH^- ions, thereby maintaining a relatively constant pH level within a specific range. This is crucial for many biological and chemical processes that are sensitive to pH changes.