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Determine amount of base to use for titration?

  1. Jun 9, 2014 #1
    1. The problem statement, all variables and given/known data
    How to find concentration of NaOH to titrate ASA with 30-40 mL

    I am doing a lab in which I need to use a base with a known concentration (a standard solution that I have to dilute to make a secondary standard) to react with an acid with an unknown concentration. I then have to find the mass of the acid.

    I am wondering how I am supposed to find what concentration my secondary standard is supposed to be. I need to use 30-40 mL of it per tablet of ASA (the acid we are using), which are 325 mg each. I guessed 0.1 mol/liter, which can be used, but doesn't follow under 30-40 mL. How do I determine the concentration of secondary standard that will give me 30-40 mL of NaOH (the base) which will dilute 325 mg of ASA dissolved in 10 mL of ethanol?

    Summary:
    - I have to make a standard solution and dilute to make a secondary standard
    - I must use NaOH (starting as a solid) as the base
    - I must use 325mg of acetylsalicylic acid as the acid with the unknown concentration
    - For best results, I should use 30-40 mL of the secondary standard to perform the titration
    - The ASA is dissolved in 10 mL of ethanol
    - I am trying to figure out the concentration of the secondary standard of NaOH that will titrate with 30-40 mL

    I tried using 0.1 mol/L of NaOH as it seemed dilute enough but not too dilute. I got values of 4g of initial NaOH. My teacher said to work backwards from the equation (ASA + NaOH -> H20 + NaASA-H) [If this is correct, I didn't type the actual chemical equation], but I do not know how that will help. He has not taught us how to calculate equivalence points.


    2. Relevant equations
    C = n/v
    n = m/M
    CiVi = CfVf


    3. The attempt at a solution
    4g of NaOH diluted to 250 mL after making a primary standard
    0.1 mol/liter --> teacher says it will work but is not optimal
     
  2. jcsd
  3. Jun 10, 2014 #2

    Borek

    User Avatar

    Staff: Mentor

    Do as your teacher said. You don't need to calculate equivalence points for that, just follow the stoichiometry.

    For that you will need to understand what is the reaction taking place. How does the acetylsalicylic acid react with NaOH?
     
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