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Homework Help: Test question: Water has pH of 7. Which solution has a [H+] concen

  1. Feb 10, 2013 #1
    Test question: "Water has pH of 7. Which solution has a [H+] concen.."


    2. First of all, increasing [H+] concentration will give something more acidic. Since every jump between pH numbers is a 10 fold difference, I thought that to make a 100 fold difference, you would have to do 10x10, which would cause the pH number to go down by two steps.

    That's why I chose A (bananas with a pH of 5).

    The actual answer is B (milk with a pH of 6).

    How does pH decrease by only 1 step?
    Would you please explain this to me?

    Thank you so much! :)
  2. jcsd
  3. Feb 10, 2013 #2


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    Staff: Mentor

    Re: Test question: "Water has pH of 7. Which solution has a [H+] conce

    IMHO your answer (pH 5, bananas) is a correct one.

    At pH 5 [itex][H^+] = 10^{-5}[/itex], at pH 7 [itex][H^+] = 10^{-7}[/itex], [itex]\frac {10^{-5}}{10^{-7}} = 100[/itex].
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