Intro to Buffers - Video Tutorials & Practice Problems
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1
concept
Acid-Base Buffers
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Acid based 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 hydro 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 p the buffer has a ph around eight. What I can do to it is I start adding acid or base. If I start adding hydro Brom acid, hydro bom acid represents a strong acid. Remember in terms of neutralization reactions, what is the chemical opposite of this hydro Bromma acid? The opposite would be the sodium fluoride, the conjugate base. So as we add hydro brom acid to the solution, the fluoride ion which is basic would interact with the hydro 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 a 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 solely neutralizing it neutralizing, it does create some acid. This causes my PH to drop. But because it's a buffer, the PH is not gonna 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, its 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 hydro 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 fluid 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 goes up 8.2. Again, I'm just showing you that the addition of a strong acid or a strong base does change the PH. But it's not gonna 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.
2
concept
Buffer Creation
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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 m make a buffer is to have either a weak acid or base with its conjugate. So for example, here we have 0.40 molar of ammonia and 0.40 mole molar of ammonium ion. We can look at this two different ways. We could say that NH three 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 first 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 would be an ideal buffer. Now, the next two ways, the second 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 um sulfurous acid here, sulfurous acid represents a weak Dipro acid. Again, you wanna 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 two molar also if uric acid, right. So just remember a buffer is a acid and base together. And these are the three specific ways to make any type of buffer.
3
example
Intro to Buffers Example
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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. Second 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 hydro fric 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 a strong base? Next we have nitric acid and ammonia. Nitric acid represents a strong acid. Ammonia represents a weak base 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 hydro cyanic 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 A BR 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 and D would be the pairs that could form a buffer solution.
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Problem
Problem
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
5
concept
Buffer Capacity
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45s
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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 changed. Here. We're going to say the larger the concentration of buffer components than the greater the buffer capacity. And we're going to say higher concentrations of weak acid and conjugate base. Remember this is the most common pair for a buffer equals better buffer, right. So basically we want more mounts of the base and acid components of a buffer so that it can more effectively neutralize any additional acid or base added to it.
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example
Intro to Buffers Example
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Which of the following combinations would make a buffer with the greatest buffering capacity. Here, we're dealing with 1 L 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 and B. We're dealing with chloric acid, which is a weak acid and we're dealing with sodium chloride. It's conjugate base for C and D. We're dealing with nitrous acid and potassium nitrite. If we take a look here, if we compare A and 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 would have a greater buffering capacity. So B would be better than A if we look at CC also has weak acid and conjugate base and the mole amounts are even larger. So option C would be better than option B. And then finally, if we're comparing C and D, we have 0.35 moles versus 0.50 moles. 0.30 moles versus 0.48 moles. Option D would 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.
7
concept
Buffer Range
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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 above a range, we have a ratio of weak acid to conjugate base. It is effective if that ratio is a 10 to 1 ratio or a 1 to 10 ratio. Basically at max, one of them can only be 10 times more than the other in terms of amount. If it go goes all in that range, it's no longer going to be an effective buffer. Here, we're gonna 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 gonna 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 10 to 1 ratio or 1 to 10 ratio when comparing your weak acid to its conjugate. So to make sure that it will be as effective as possible
8
example
Intro to Buffers Example
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2m
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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 10 to 1 or 1 to 10 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 they could equal to one, that's the best type of buffer. So what we're gonna 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 close to one would be mo most ideal and therefore most effective buffer. So if we take a look here in all 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 plus. So this would be the conjugate base. All we're gonna do here is we're gonna 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 1.0 over 1.2 which comes out to 0.83. For me, 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 six 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 ratio, the one closest to one is option A option A would represent the pairing that is the most ideal buffer and therefore the most effective buffer. Now, if they asked 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, on the edge of our buffer range, right? So keep in mind for this particular one, the answer is option A.
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Problem
Problem
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
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