### 12.57

Posted:

**Mon Dec 04, 2017 11:40 pm**How do we know the answer in 12.57 will only be one sig fig? I used two and it gave a pretty different answer (.10 versus the book's .09). Thanks!

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=59&t=24529

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Posted: **Mon Dec 04, 2017 11:40 pm**

How do we know the answer in 12.57 will only be one sig fig? I used two and it gave a pretty different answer (.10 versus the book's .09). Thanks!

Posted: **Tue Dec 05, 2017 10:18 am**

Since the sigfigs in the question is all 2 or 4, i assume that your answer would be correct. I'm assuming it's just an error in the solution manual.

Posted: **Tue Dec 05, 2017 4:42 pm**

Can someone please explain how to do this problem? I've been trying to do it for over thirty minutes now.

Posted: **Tue Dec 05, 2017 5:21 pm**

For part a, since you are given the pH value of HClO2, you can first calculate the molarity of H3O+. Then, you get the molarity of its conjugate base as it is the same as the hydronium ions. The question you probably have when calculating Ka is the equilibrium concentration of HClO2, which you get by subtract the amount deprotonated from the original molarity. From here, you can get pKa. And part b is the same process of part 1.