0.110 M in formic acid and 5.5×10−2 M in hypochlorous acid . How to find pH

Note: Dr Rebel has reversed the Ka values (as well as using my estimates instead of the tabular values for Ka) AND calculated as if the acids were alone and not in a mixture.

Look up Ka values. Formic acid is about 10^-4 and HClO is about 10^-8 so formic acid is a much stronger acid. Also there is more of it. I would be tempted to ignore the HClO and calculate pH from HCOOH alone.

Well, in order to find the pH, we need to take into account the dissociation of these acids. But hey, let's not go through all that boring chemistry stuff. Instead, let's call in our pH experts, the pHizards! These magical creatures will make it much more fun.

So, we have some formic acid floating around, doing its thing. And we also have hypochlorous acid, just chilling. Now, each of these acids will release some hydrogen ions (H+) when they dissociate in water. These little guys are the ones that determine the pH.

Since these acids have different dissociation constants, the pH of the solution will depend on the relative concentrations of the hydrogen ions released by each of them. So, it's like a fancy acid battle happening in your solution!

But wait, why don't we just add their concentrations together and call it a day? Well, because the pHizards won't let us. They want us to pay attention to how the acids behave individually. So, let's respect their wishes.

Now, to find the pH, we need to calculate the hydrogen ion concentration for each acid separately, using their respective dissociation constants. Then, we can add these concentrations together and find the overall concentration of hydrogen ions in the solution. And the best part is, once we have that, the pH is simply the negative logarithm of that concentration. Easy peasy lemon squeezy!

So, grab your calculator, channel your inner pHizard, and get ready to calculate the pH of this acid party!

To find the pH of a solution, you need to know the concentration of an acid and its dissociation constant (Ka) value. In this case, you have the concentrations of formic acid (HCOOH) and hypochlorous acid (HOCl).

To determine the pH, follow these steps:

1. Write the balanced equation for the dissociation of the acids:
a) HCOOH ⇌ H⁺ + HCOO⁻
b) HOCl ⇌ H⁺ + OCl⁻

2. Find the dissociation constant (Ka) values for both acids. For formic acid (HCOOH), the Ka value is 1.77 × 10⁻⁴. For hypochlorous acid (HOCl), the Ka value is 3.0 × 10⁻⁸.

3. Determine the concentrations of H⁺ (protons) for both acids. Since both acids fully dissociate in water, the concentration of H⁺ will be equal to the initial concentration of the acid.

For formic acid: [H⁺] = 0.110 M
For hypochlorous acid: [H⁺] = 5.5 × 10⁻² M

4. Use the Ka values and concentrations of H⁺ to calculate the pH using the Henderson-Hasselbalch equation:

For formic acid: pH = -log([H⁺]) = -log(0.110) = 0.96
For hypochlorous acid: pH = -log([H⁺]) = -log(5.5 × 10⁻²) = 1.26

Therefore, the pH of the formic acid solution is approximately 0.96, and the pH of the hypochlorous acid solution is approximately 1.26.

For weak acids in pure water ...

pH = -log[H^+]
[H^+] = SqrRt[(Ka)(Molar Conc of Acid)]

HClO:
[H^+]=(SqrRt[(10^-4)(0.055)])M
= 0.0024M
pH=-log(0.0024)=-(-2.63)=2.63

HCOOH:
[H^+]=(SqrRt[(10^-8)(0.110)])M
=3.32E-5M
pH=-log(3.32E-5)=-(-4.50)=4.50