Achieve 2 Question 3

[Tina Karami 2K]

Hi, I'm stuck on calculating the pH and pOH on question 3. I was able to solve for the percent ionized and used the quadratic equation to get the x value. However, when I do the -log(x), it says my value for the pH is wrong because I didn't use the quadratic formula. I was wondering if anyone can tell me where my error is?

[Ann_Ding_1J]

Hi,

It looks to me like it's just a matter of significant figures. Remember that when you take the log of a number, you count the sigfigs and keep that many decimal places in the answer. Therefore, in this problem, you would have 2 decimal places because the number you took the log of had 2 sigfigs. Hope that helps.

[Ann_Ding_1J]

To add as a quick note,
The pH and pOH you get with the quadratic formula and the pH/pOH you get without the quadratic formula are extremely close (it was a difference in the hundredths), so incorrectly counting the sigfigs can easily cause the achieve program to assume that you didn't use the quadratic formula in the feedback comments.