Finding pH given molarity and volume

  1. 1. The problem statement, all variables and given/known data
    If you mix 200mL of a 1.8M HCl solution with 300mL of a 1.16M NaOH solution, what will be the pH of the solution?

    3. The attempt at a solution
    Well im really lost with this problem. Im pretty sure you need to convert each to moles.

    .2L HCl x 1.8moles HCl
    1L HCl

    .3L NaOH x 1.16 moles NaOH
    1L NaOH



    HCl + NaOH -> NaCl + H2O

    not too sure where u go from there
  2. jcsd
  3. symbolipoint

    symbolipoint 3,073
    Homework Helper
    Gold Member

    The acid and the base react 1:1, so which is in excess, and by how much?
  4. is it .36-.348=.012 moles of HCl which = number of H+ ions?

    pH=-log(.012) = 1.92?
  5. or do u have to change moles of HCl back to molarity?

    .012moles HCl
    .5L total


  6. symbolipoint

    symbolipoint 3,073
    Homework Helper
    Gold Member

    HCl in aqueous solution is strongly ionized, or completely ionized for most practical purposes. For pH, you want the hydrogen ion CONCENTRATION AS MOLARITY...., and then find the negative logarithm.
    Last edited: Apr 27, 2008
  7. yea so itd be 1.62 right?
  8. Borek

    Staff: Mentor

    Yep, 1.62 it is.
  9. chemisttree

    chemisttree 3,723
    Science Advisor
    Homework Helper
    Gold Member

    Welcome back, Borek! You were missed.
  10. Borek

    Staff: Mentor


    I am planning to spend some time here now ;)
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