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Homework Help: AP Chem Acid and Base Equilibria

  1. Apr 15, 2010 #1
    1. The problem statement, all variables and given/known data

    OK so this is my first time actually posting but I have lurked around. I need help with two of my chemistry problems.

    Problem 1

    Decide which one(s) of these answer choices are correct.
    A buffered solution is one which can be desribed by which of the following:

    I. a solution which resists pH
    II. may contain a weak acid and its salt
    III. contains species which can react with both H+ and OH-

    Problem 2

    Which of the following salts will form a basic solution in water?
    a. KCl
    b. Na2SO4
    c. CuCl2
    d. Na2CO3
    e. NH4NO3

    2. Relevant equations

    No equations for question 1.

    Question 2 wouldn't the products have to have the OH ion or will water autoionize?

    3. The attempt at a solution

    For problem 1 I already know that answer choices "I and II" are correct. My question is about the third. I don't understand what the statement is saying and whether it is true or not.


    For question 2 I thought that what reacts with water will have to have an OH- to become a basic salt.

    Thanks to those who can help
     
  2. jcsd
  3. Apr 15, 2010 #2
    a buffered solution is a solutions which resists change in pH. So what you have initially say is a weak acid and a weak base. Lets say you add a strong acid like HCl, which has a low pH, and will generally make your solution more acidic. Once you do this, your weak base will react with the strong acid, creating a weak acid and possibly water. So now that strong acid will in a way be converted to a weak acid, only slightly decreasing the pH.


    For the second one, you basically want to split up the two components of each molecule. It seems that a bunch of them have strong acid components, and a bunch of them have strong base components. You might have to do some log[OH] and log[H] calculuations. So basicaly we know NaOH is a strong base, so chances are that one will create a strong base. we Know HNO3 is a strong acid, so that one will not be basic. and so on.
     
  4. Apr 15, 2010 #3

    Borek

    User Avatar

    Staff: Mentor

    Imagine solution of acetic buffer. It contains both CH3COO- and CH3COOH. What happens when you add base? What happens when you add acid?

    Do you know what is Broensted definition of a base? Do you know how ammonia reacts with water and why its solutions are basic? Can you write reaction equation? Or perhaps you have neard about hydrolysis?

    --
    methods
     
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