What is the pH of a 0.400 molar HCl solution?
I did -log(.4)=.398. That seems too low. I think I need to find the molarity (M) of the solution, but I can't find it with the given information.
You can't? 0.400 molar is 0.400 M.
The pH looks ok to me. 1 M HCl has pH of 0 so 0.400 M should be just a bit higher and it is.
Okay thank you. I didn't realize they were the same.
But in "What is the pH of a 0.300 molar NaOH solution?" -log(.3)=.523 is incorrect. Why?
Because you calculate the pOH, not the pH. Since NaOH ==> Na^+ + OH^- then the OH is 0.3 M.
To convert from pOH to pH it is
pH + pOH = pKw = 14. Knowing pKw and either of the others, you can interchange pH ad pOH quickly and easily.
To calculate the pH of a solution of a strong acid like HCl, you don't need to know the molarity (M) of the solution. The pH of a solution can be determined using the concentration of the hydrogen ions (H+), which is given by the molarity of the acid.
Since HCl is a strong acid, it completely dissociates in water, and one mole of HCl produces one mole of H+ ions. Therefore, the concentration of H+ ions in the solution is equal to the molarity of HCl.
In this case, the molarity of the HCl solution is given as 0.400 M, which means there are 0.400 moles of HCl in 1 liter of the solution.
To calculate the pH, you can simply take the negative logarithm (base 10) of the H+ ion concentration.
Using the given concentration, the pH can be calculated as follows:
pH = -log[H+]
pH = -log(0.400)
pH ≈ 0.4
So, the pH of the 0.400 M HCl solution is approximately 0.4.