How to calculate pH of HCl in water?

Calculate [H+], [OH-], and the pH for this solution.?

• A solution is prepare by mixing 90.0 mL of 5.00 M HCL and 30.0 mL of 8.00 M HNO3. Water is then added until the final volume is 1.00 L. Calculate [H+], [OH-], and the pH for this solution.

• Answer:

  Calculate total H+ concentration 0.09L x 5 mol/L = 0.45 moles H+ from HCl 0.03L x 8 mol/L = 0.24 moles H+ from HNO3 Total H+ = 0.45 + 0.24 = 0.69 moles in 1 liter = 6.9x10^-1M So [H+] = 0.69 M = 6.9x10^-1M pH = -log [H+] = -log 0.69 = 0.16 [H+] x [OH-] = 1x10^-14 so [OH] = 1x10^-14 / 6.9x10^-1 = 1.45x10^-12M