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Homework Help: Confusing Chem

  1. Sep 9, 2010 #1
    1. The problem statement, all variables and given/known data
    25 cm3 of 1 mol/dm3 ethanoic acid requires a smaller amount of sodium hydroxide for complete neutralisation than 25 cm3 of 1 mol/dm3 hydrochloric acid.
    True or False?

    2. The attempt at a solution

    I selected true, but I was wrong. Both of them require the same amount of sodium hydroxide. How can this be?

    Question 2:

    In a dilute sugar solution, sugar molecules are widely separated, moving at random while water molecules are close together, moving at random.
    True or False?

    Attempt

    I selected False. But I was wrong AGAIN! What's the reason?

    Could you all help me with my questions. Thanks!
     
  2. jcsd
  3. Sep 9, 2010 #2

    Borek

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    Staff: Mentor

    Why do you think they need different amount of base?

    Similarly, try to explain your reasoning behind the answer to the second question.

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  4. Sep 9, 2010 #3
    I think they need different bases cause ethanoic acid is a weak acid while HCL is a strong acid, thus you need more NaOH to neutralise a strong acid than a weak acid.

    I figured out the second qns though, but I remember a qns vaguely about alcohol being dissolved into water and the mixture seems to have mass that didn't add up to the mass of water and alcohol or something like that. I didn't know whether it is the mass, density or volume that didn't add up.
     
  5. Sep 9, 2010 #4

    Borek

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    Staff: Mentor

    Write reaction equations both for HCl and acetic acid neutralization with NaOH.

    How much base needed to neutralize 1 mole of each acid?

    Volume is not additive. Mass is additive, that's mass conservation in action. But I fail to see how volume being not additive is relevant to the question.
     
  6. Sep 9, 2010 #5
    Both require 1 mole... But even if both acids have 1 mole of particles, HCL would have more hydrogen ions since ethanoic acid dissociates partially and there would be CH3COOH molecules left intact in the water.

    I figured out qns 2. Thanks.
     
  7. Sep 9, 2010 #6

    Borek

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    Staff: Mentor

    You are mistaking dissociation with neutralization. Yes, pH of HCl solution is lower than pH of acetic acid solution, no, it doesn't mean it requires more base for neutralization.

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