Find the pH of each mixture of acids.

Question

Find the pH of each mixture of acids.

0.020 M HBr and 0.015 M HClO4.

They are both strong acids Si they dissociate completely. Si do I just add 0.020 and 0.015 and take the -log of that concentration to get the pH?

Like thus....
0.020+0.015=0.035
pH=-log(0.035)
pH=1.46

Would this be right?

Answer 1

Well, if I were an acid, I'd say your calculation is a bit acidic itself. Let's look at it again.

Since both HBr and HClO4 are strong acids, they will dissociate completely. So, the concentration of hydrogen ions (H+) in the mixture will be the sum of the individual concentrations.

0.020 M HBr + 0.015 M HClO4 = 0.035 M H+.

But remember, the pH is calculated using the negative logarithm of the concentration of H+ ions. So, the pH of the mixture would be:

pH = -log(0.035) ≈ 1.46.

Great job, you got it right! Just remember to always keep a pHlan on hand for all your acid calculations.

Answer 2

No, that would not be correct. When you have a mixture of strong acids, you cannot simply add their concentrations together. The pH of a solution depends on the individual concentrations of each acid and their respective dissociation constants.

In this case, you need to consider the individual dissociation constant (Ka) of each acid and calculate the concentration of H+ ions from each acid separately. Then you can combine the concentrations of H+ ions to determine the pH of the mixture.

For HBr:
HBr → H+ + Br-
The dissociation constant (Ka) for HBr is very high, so it can be assumed that it dissociates completely. Therefore, the concentration of H+ ions from HBr is equal to the concentration of HBr itself, which is 0.020 M.

For HClO4:
HClO4 → H+ + ClO4-
Again, the dissociation constant (Ka) for HClO4 is very high, so it dissociates completely. The concentration of H+ ions from HClO4 is equal to the concentration of HClO4 itself, which is 0.015 M.

Now, you can combine the concentrations of H+ ions:
[H+] = [H+ from HBr] + [H+ from HClO4]
[H+] = 0.020 M + 0.015 M
[H+] = 0.035 M

Finally, you can find the pH using the equation pH = -log[H+]:
pH = -log(0.035)
pH ≈ 1.46

So the correct pH of the mixture of 0.020 M HBr and 0.015 M HClO4 is approximately 1.46.

Answer 3

To find the pH of an acidic solution, you need to calculate the hydrogen ion concentration ([H+]) first. Since both HBr and HClO4 are strong acids that dissociate completely, you can assume that the concentration of [H+] from each acid is equal to the initial concentration of the acid itself.

So, in this case, you can find the [H+] concentration of each acid separately and then add them together.

For HBr:
[H+] = 0.020 M

For HClO4:
[H+] = 0.015 M

To find the total [H+] concentration, you add these two values:
[H+]total = [H+]HBr + [H+]HClO4
[H+]total = 0.020 M + 0.015 M
[H+]total = 0.035 M

Now that you have the total [H+] concentration, you can use the formula pH = -log[H+] to find the pH:
pH = -log(0.035)
pH ≈ 1.46

So your calculation is correct, and the pH of the mixture of 0.020 M HBr and 0.015 M HClO4 is approximately 1.46.

Answer 4

There is something missing in these problems; namely, how much of each is being mixed. It's obvious that if I take 1 L of 0.020 M HBr and mix it with 1 mL of 0.015M HClO4 that the pH will be different from a mixture of 1L 0.015 M HClO4 + 1 mL 0.020 M HBr. From the previous posts on this same kind of question, I think you have done this right but I still don't like the question. It's ignoring the dilution factor of each acid on each other. And it's giving the student the idea that all we need is the molarity to calculate pH of mixtures. The earlier problems (with HCOOH + CH3OOH as well as with HClO4 + HCOOH) the volume didn't matter as much. In the HClO4/HCOOH mixture the HCOOH contribution was so small it was not added in; however, it still would have diluted the strong acid.