Explain why a mixture formed by mixing 100 mL of 0.100M CH3COOH and 50 mL of 0.100M NaOH will act as a buffer? in adittion to this, how do you identify if a an aqueous solution is a buffer solution, such as a solution with an acid and a base, but no common ion? is it possible to have such a buffer?
NaOH is a strong base; it reacts with CH3COOH, a weak acid, as follows:
CH3COOH + NaOH ==> CH3COONa + HOH
Since you began with 10 millimoles CH3COOH and 5 millimoles of NaOH, you will produce 5 millimols of the salt (CH3COONa) and you will have left over, at equilibrium, 5 millimoles CH3COOH un-reacted.
You have a solution of a weak base and its salt. So why is this a buffer?
Acetic acid ionizes like this:
CH3COOH + H2O ==> CH3COO^- + H3O^+
Sodium acetate ionizes like this:
CH3COONa ==> CH3COO^- + Na^+
Here's the skinny.
If you try to change the pH of the solution by adding a strong base (NaOH for example), the OH^- are neutralized by the free acetic acid in solution and the pH changes very little. If you try to change the pH by adding a strong acid (HCl for example), the acetate ions (from the sodium acetate) react as follows:
CH3COO^- + H^+ ==> CH3COOH to form acetic acid which just adds a little more acetic acid to what whatr there already. The pH changes little. Within reason, then, addition of strong acid or strong base changes the pH very little. That's why it's a buffered solution.
A buffered solution consists of a weak acid and its salt OR a weak base and its salt. An example of the first isl acetic acid and sodium acetate; an example of the second is ammonia and ammonium chloride.
The last part of your question is yes if you make it. That is, notice the problem started out with acetic acid (an excess) and a strong base (NaOH) which MAKES the salt and leaves some of the acetic acid around. The only other kind I can think of is ammonium acetate. This is the salt of a WEAK acid (acetic acid) AND a WEAK base (NH3)(aq).
thank you....i understand the concept clearly now.
Well, well, let's dive into the world of buffers, shall we? So, when you mix 100 mL of 0.100M CH3COOH (which is acetic acid for the non-chemistry enthusiasts out there) with 50 mL of 0.100M NaOH, a lovely little reaction takes place. The NaOH reacts with the CH3COOH to form CH3COONa (Acetate ion) and water. Now, here's the magic trick that makes this mixture a buffer: acetic acid and the acetate ion are a conjugate acid-base pair!
Now, why is this important? Well, buffers are marvelous concoctions that resist changes in pH. When an acid or base is added to a buffer solution, the conjugate acid-base pair in the buffer reacts and prevents a drastic change in pH. In this case, if an acid is added, the CH3COONa (the conjugate base) will react with it. And if a base is added, the CH3COOH (the conjugate acid) will react with it. So, you've got a dynamic duo keeping that pH in check!
Now, to recognize if an aqueous solution is a buffer, even without a common ion, we need two components: a weak acid (or weak base) and its conjugate base (or acid). You see, even if you don't have an excess of a common ion, as long as you have this acid-base pair, you've got yourself a buffer! It's like having Batman and Robin with matching capes, but without a third-wheel sidekick getting in the way.
As for the possibility of having a buffer without a common ion, you've got it! That's what we just talked about. As long as you have the lovely conjugate acid-base pair, you can enjoy the buffer party without worrying about any unwanted common ions crashing the scene. It's all about that dynamic duo chemistry!
So, mix up some acids and bases, and let those buffers do their pH-resisting magic!
To understand why the mixture formed by mixing 100 mL of 0.100M CH3COOH (acetic acid) and 50 mL of 0.100M NaOH (sodium hydroxide) acts as a buffer, we need to consider the properties of a buffer solution.
A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal concentrations. It has the ability to resist changes in pH when small amounts of acid or base are added to it.
In this case, CH3COOH is a weak acid, and when it reacts with NaOH, it forms its conjugate base, CH3COO-. The reaction can be represented as:
CH3COOH + NaOH -> CH3COO- + H2O
The resultant solution contains a significant amount of both CH3COOH and CH3COO-, making it a buffer solution.
To identify if an aqueous solution is a buffer, several criteria can be considered:
1. It contains a weak acid and its conjugate base (or a weak base and its conjugate acid).
2. The concentrations of the acid and base components are approximately equal or close to being equal.
3. The pH of the solution remains relatively constant even with the addition of small amounts of acid or base.
In this case, because we have mixed CH3COOH, a weak acid, and NaOH, a strong base, without any common ion, the solution initially does not meet the criteria of having a buffer solution. However, once the reaction between the weak acid and base occurs, it forms the weak acid's conjugate base, which allows the solution to act as a buffer.
Therefore, while it is not possible to have a buffer solution with just an acid and a base without any common ion, the addition of the base to the weak acid creates the necessary conjugate base, enabling the resulting solution to function as a buffer.
A mixture formed by mixing 100 mL of 0.100M CH3COOH (acetic acid) and 50 mL of 0.100M NaOH (sodium hydroxide) will act as a buffer because it contains both a weak acid and its conjugate base. In this case, acetic acid (CH3COOH) is the weak acid, and its conjugate base, acetate ion (CH3COO-), is formed when CH3COOH donates a proton (H+). Similarly, NaOH is a strong base that dissociates completely to produce hydroxide ions (OH-).
When the acidic acetic acid and basic sodium hydroxide are mixed, a neutralization reaction occurs, resulting in the formation of water and the acetate ion:
CH3COOH + NaOH -> CH3COO- + H2O
The presence of both the weak acid and its conjugate base allows the mixture to resist changes in pH when a small amount of acid or base is added. If an acid is added, it will react with the basic acetate ion, shifting the equilibrium to the left to restore the balance:
CH3COO- + H+ -> CH3COOH
If a base is added, it will react with the acidic acetic acid, shifting the equilibrium to the right:
CH3COOH + OH- -> CH3COO- + H2O
In this way, the buffer can maintain its pH within a certain range even when small amounts of acid or base are introduced.
To identify if an aqueous solution is a buffer solution, you need to check if it contains both a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer solution requires these two components to resist changes in pH. It is not possible to have a buffer solution without a weak acid and its conjugate base or a weak base and its conjugate acid. Without at least one of these components, the solution would not have the ability to "buffer" or resist pH changes effectively.