Comparing a hydronium with a hydroxide in a weak acid solution (0.1M)

In summary: H3O+.In summary, the conversation discusses the molarity of OH- and H3O+ in an aqueous solution of a 0.1M weak acid. There are two possible answers: 1) [H3O+]>[OH-] because there are no hydroxides involved and 2) [H3O+]=[OH-] due to water self-ionization. However, the correct answer is [H3O+]>[OH-] as the acid solution also contributes to the H3O+ concentration. The conversation also mentions the water autodissociation and the water ion product, Kw, as well as links to sources for further understanding. There is also a discussion
  • #1
HazyMan
51
3
TL;DR Summary
I am trying to find out why the hydronium molarity is greater than the hydroxide molarity in this solution of a weak acid "HA".
This question says: An HA weak acid solution with a molarity of 0.1M is dissolved in water. In the new solution, is the molarity of OH- greater than the H3O+ molarity, or the opposite? Or are they equal?

I came up with two possible answers:

1. [H3O+]>[OH-] because there are no hydroxides involved at all, but this leads me to the second answer, which IS wrong according to my solution book but i just wanted to mention it..

2 [H3O+]=[OH-]. I came up with this because if you replace "A" with a hydroxide, you will end up with HOH+H2O<->H3O+OH which is basically water self-ionization.

I'm just not sure if my first answer is correct either, because the solution book simply says that [H3O+]>[OH-], implying that hydroxides are indeed involved.

Is my answer (the first one) correct?
 
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  • #2
Are you aware of the water autodissociation? Do you know what the water ion product is?

(if not: google them)
 
  • #3
Borek said:
Are you aware of the water autodissociation? Do you know what the water ion product is?

(if not: google them)
That's what i thought of regarding the second answer i came up with. However if that was the case, wouldn't the hydronium molarity be equal to the hydroxide one? In the book it says that this is not the correct answer.
I didn't think of the ion product. If i substitute that in then i get Kw=([H3O+][OH-])/[HA]
 
  • #4
HazyMan said:
wouldn't the hydronium molarity be equal to the hydroxide one?

In a pure water - yes. But you have an acid solution, so there is more than one source of H+.

If i substitute that in then i get Kw=([H3O+][OH-])/[HA]

No idea what you did here nor how, but it is definitely wrong.
 
  • #5
Borek said:
In a pure water - yes. But you have an acid solution, so there is more than one source of H+.
No idea what you did here nor how, but it is definitely wrong.

Isn't the water ion product notated as Kw? Isn't it an equilibrium constant?
 
  • #6
HazyMan said:
Isn't the water ion product notated as Kw? Isn't it an equilibrium constant?

Yes to both, it still doesn't make the formula correct.

If it is equilibrium just for water, why do you put HA there?
 
  • #7
Borek said:
Yes to both, it still doesn't make the formula correct.

If it is equilibrium just for water, why do you put HA there?
i forgot that OH was substituted in A. So it's Kw=[H3O+][OH-] ?
 
  • #10
Wait, i think i realized something. All along i thought i had to replace A with OH but now i get what's going on. I'm supposed to compare the overall H3O+ concetration with the OH- concetration which is only produced by the water's self ionization, which as a phenomenon, is known to be quite rare. So it is obvious that H3O has a bigger concetration simply because of the HA acid being dissolved ALONG with the water
 

1. What is the difference between hydronium and hydroxide ions in a weak acid solution?

Hydronium (H3O+) and hydroxide (OH-) ions are both present in a weak acid solution. The main difference between them is their concentration and their role in the solution. Hydronium ions are formed by the reaction of the weak acid with water molecules, while hydroxide ions are formed by the dissociation of water molecules. In a 0.1M weak acid solution, the concentration of hydronium ions will be higher than that of hydroxide ions.

2. How do hydronium and hydroxide ions affect the pH of a weak acid solution?

The concentration of hydronium and hydroxide ions in a solution determines its pH. In a weak acid solution, the concentration of hydronium ions will be higher than that of hydroxide ions, making the solution acidic with a pH less than 7. However, as the weak acid dissociates, the concentration of hydroxide ions will increase, causing the pH to rise and become more alkaline.

3. Can you compare the strength of hydronium and hydroxide ions in a weak acid solution?

In a 0.1M weak acid solution, the concentration of hydronium ions will be higher than that of hydroxide ions. This indicates that hydronium ions are stronger than hydroxide ions in this solution. However, it is important to note that the strength of these ions can vary depending on the concentration of the weak acid and the temperature of the solution.

4. How does the concentration of the weak acid affect the concentration of hydronium and hydroxide ions in a solution?

The concentration of the weak acid directly affects the concentration of hydronium and hydroxide ions in a solution. As the concentration of the weak acid increases, more hydronium ions will be formed, leading to a decrease in the concentration of hydroxide ions. This will result in a lower pH and a more acidic solution.

5. What is the role of hydronium and hydroxide ions in a weak acid solution?

Hydronium and hydroxide ions play a crucial role in maintaining the pH of a weak acid solution. The concentration of these ions determines the acidity or alkalinity of the solution. In addition, hydronium ions also play a role in the dissociation of the weak acid, while hydroxide ions can neutralize excess hydronium ions to maintain a balance in the solution.

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