[Inneedofhelp]

Hello. I am taking a beginner's chemistry course but I am lost doing a worksheet.

One question asks for the pH in a 0.1M solution of formic acid, given pKa = 3.75

I plugged in the values into the definition of pKa and got 0.004129 as the concentration of H3O⁺ ions.
This can be used to find the pH.

But I am unsure about the next problem.

It asks for a calculation of the pH in a solution of 10ml 0.10M formic acid and 11ml 0.10M NaOH.

My idea was to use the concentration of H3O+ from the first question, 0.004129, and multiply this by the volume (0.01L) of formic acid to find the molar amount of H3O+. On the basis of NaOH being a strong base, I assume 0.10 moles of OH-. Then I simply subtract the molar amount of OH- by the molar amount of H3O to find the resulting molar amount of OH-. I take this molar amount and divide by 0,021 to find M, plug this into the -log function for pOH, from which pH can be found.

This solution might be completely incorrect. Apologies for any mistakes and many thanks for any assistance.

[Borek]

I plugged in the values into the definition of pKa and got 0.004129 as the concentration of H3O⁺ ions.

No idea what you really did, burt the answer seems to be in a correct ballpark.

It asks for a calculation of the pH in a solution of 10ml 0.10M formic acid and 11ml 0.10M NaOH.

They reacted, didn't they?