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Very Quick Chemistry Question

  1. Oct 31, 2011 #1
    Hey, I'd appreciated an answer to a really basic chemistry question.

    If I increase the volume of 1.0 mol/L hydrochloric acid from 50mL to 100mL, does that change the concentration?

    Will an antacid tablet dissolve more quickly in 50mL or 100mL of hydrochloric acid?
     
  2. jcsd
  3. Nov 1, 2011 #2

    Borek

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    Staff: Mentor

    What do you mean by "increase the volume"? Do you add more acid, or do you dilute it with water?

    Same concentration of acid?
     
  4. Nov 1, 2011 #3
    Either way, the concentration will change. Look at how you measure concentration: moles per litre. More moles of HCl will make the fraction bigger => higher concentration. If you add more water, the fraction will be smaller, and your concentration will be lower.

    On a side note, HCl in aqueous solution exist as H+ and Cl-. That's why it's a strong acid, total protonation.


    As to your tablet question. Consider this: when you dissolve something in water, you have a finite "bonding places". When that number is reached, your solution is saturated, and you can't solve more. The closer you get to your saturation point, the slower the solving will take. This rate is decreasing exponentially. Not sure if that made any sense....
     
  5. Nov 1, 2011 #4

    Borek

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    Staff: Mentor

    Not necessarily, although I see what I posted was ambiguous. What I meant by "adding more acid" was "adding more acid solution". Concentration is an intensive property and doesn't depend on the amount of the solution.

    It is not wrong, but to know if it applies you will have to check the stoichiometry and solubility. Could be we are very far from the saturation.
     
  6. Nov 1, 2011 #5
    We have 10mL 1M HCl.

    1. add 30mL 1M HCl to original solution: won't affect concentration of HCl.
    2. add 30mL 2M HCl to original solution: will affect concentration of HCl to 1,333M
    3. add 30mL pure water to original sollution: will reduce [HCl] to 0,04M

    If one tablet will saturate 5mL water, then there probably won't be much difference in the dissolving rate in 50mL water and 100mL water. Should one tablet, however, saturate 105mL water, then I guess there will be. Just an example of course.
     
  7. Nov 2, 2011 #6
    Check your calculations for 2 and 3, but the direction of the effect is right.
     
  8. Nov 2, 2011 #7
    Ohh, yeah, too fast in the turns!


    2. is supposed to be 1.75M
    3. is supposed to be 0,25

    Not sure what I was doing, lol
     
  9. Nov 5, 2011 #8
    [tex]concentration = \frac{mol}{Volume}[/tex]

    What do you think what happens to concentration if you duplicate volume?
     
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