Hi,
The problem is:
"Calculate the concentration of OH- and the pH value of an aqueous solution in which [H30+] is 0.014M at 25C. Is this solution acidic, basic, or neutral?"
I have calculated the OH- concentration to be: 7.1 X 10^-14
When I calculate the pH (using H30+), I get a pH of .85. Is that possible? If I calculate using OH-, I get a pH of 13.15. With such widely different answers, I want to be sure I am doing this right.
This is an online class, so no lecture to rely on for help! Thanks!
You're right to be confused. I get 1.85 for pH (which makes it an acid solution).
pH = -log(H^+) = -log(0.014) = -(-1.85) = 1.85. Then for OH^-, I do it this way.
pH + pOH = pKw = 14
1.85 + pOH = 14 which makes pOH = 14 - 1.85 = 12.15
Then solve pOH = -log(OH^-)
12.15 = -log(OH^-)
(OH^-) = 7.14 x 10^-13
Thank you!
To determine the concentration of OH- and the pH value of the aqueous solution, you can use the equation:
Kw = [H3O+][OH-]
Where Kw is the ion product of water, which is equal to 1.0 x 10^-14 at 25°C. Since you have the concentration of H3O+ as 0.014M, you can rearrange the equation to solve for OH- concentration:
[OH-] = Kw / [H3O+]
[OH-] = (1.0 x 10^-14) / (0.014)
Calculating this value, you should get [OH-] = 7.14 x 10^-13 M, which is different from your result of 7.1 x 10^-14 M. It's important to double-check your calculation for the OH- concentration to ensure accuracy.
Now, let's calculate the pH value. The pH is a logarithmic measure of the hydrogen ion concentration, defined as:
pH = -log[H3O+]
Using your given H3O+ concentration of 0.014M, you can calculate the pH:
pH = -log(0.014)
pH ≈ 1.85
So, it seems that your calculation of pH as 0.85 is incorrect. The correct result should be approximately 1.85.
As for calculating the pH using the OH- concentration, it can be done using the equation:
pOH = -log[OH-]
Since you have already calculated [OH-] as 7.14 x 10^-13 M, you can determine the pOH:
pOH = -log(7.14 x 10^-13)
pOH ≈ 12.15
Now, to find the pH, you can use the equation:
pH = 14 - pOH
pH ≈ 14 - 12.15
pH ≈ 1.85
Notice that both methods yield the same pH value of approximately 1.85. This is expected as pH and pOH are complementary parameters representing the acidity or basicity of a solution.
Therefore, this aqueous solution with a pH of approximately 1.85 is considered acidic, since it has a higher H3O+ concentration compared to the OH- concentration.