Calculating pH and pOH of NaOH

[Aya Watson 2B]

How would I calculate the pH and pOH of the following:

13.6 mg of NaOH dissolved in 0.350 L of solution

I started by converting the mg to mols using the molar mass of about 40. This got me .54, and then I divided that by the volume .35L to find Molarity. I got 1.55 which gives me an incorrect pH and pOH.

[SarahOMalley1D]

Hi! I think you may have forgotten to convert from mg to g before converting from g to mol. There are 1000 milligrams in 1 gram, so 1000 mg=1g. You can use this conversion factor to convert your initial amount of NaOH before moving forward in the problem.

[Aya Watson 2B]

Hi! I think you may have forgotten to convert from mg to g before converting from g to mol. There are 1000 milligrams in 1 gram, so 1000 mg=1g. You can use this conversion factor to convert your initial amount of NaOH before moving forward in the problem.

Hi! I did originally convert it from 13.6 mg to .0136 g so I'm still not sure where I went wrong..

[Hayden Jackson]

If you have NaOH, you know that for 1 mole NaOH, you have 1 mole OH-, which is what you are trying to find the concentration of, not NaOH as a whole. Your molar mass should not be 40. That would mean that you are calculating the molarity of NaOH as opposed to just the molarity of OH-. The molar mass of OH- should be around 17, so use that when finding the number of moles of OH- and that should give you the right answer. Hope this helps!