How to measure concentration

  1. I was wondering if anyone knows how to measure concentration.
    I'm gonna have a lab prac. where we design an experiment to investigate the effect of concentration in the rate of reaction of calcium carbonate and hydrochloric acid.
    I already know that increasing the concentration will increase the rate of reaction but I have no idea how to design a fair test to prove that hypothesis!!
    Help me out if you can plz.....

    Thanx 2 any who rply....
    From:
    <<o:) De LiL AgeLu o:) >>
     
  2. jcsd
  3. Hootenanny

    Hootenanny 9,681
    Staff Emeritus
    Science Advisor
    Gold Member

    If you are only required to investigate the effect of concentration of rate, it is not nesscary to calculate the concentration of either reactants. It is usually enough simply to determine the relationship between the two. Here, you should vary the concentration of one of the reacants, while keeping the other one constant (I would recommend varying the HCl conc and keeping the calcium carbonate chips of roughly equal surface area).

    ~H
     
  4. Even if you do not calculate the concentration in this experiement it could be interesting for you to find out. Here are some good links for the concept of concentation:

    http://en.wikipedia.org/wiki/Concentration
    http://chemistry.about.com/library/weekly/aa081003a.htm
    http://www.google.se/search?hl=sv&q=define:concentration&btnG=Google-sökning&meta=

    Concentration can be calculated via two forumlae, depending on if you are diluting a substance or if you want to find the concentration of eg. a certain amount (in mole) of a substance dissolved in a certain amount of solvent.

    Don't hesitate to ask if there is something you do not understand completely :smile:

    A basic knowledge of the concept of mole is good to have if one is dealing with concentration.

    [tex]n[/tex] = [tex]m/M[/tex]

    [tex]n[/tex] = number of mol
    [tex]m[/tex] = Amount of mass (in grams)
    [tex]M[/tex] = Relative molar mass / Relative Atomic mass (look at the O for Oxygen in a periodic table and you will see "16" (or "15.9994" depending on the accuracy of it).

    [tex]n[/tex] = [tex]V * C[/tex]
    [tex]V_1 * C_1[/tex] = [tex]V_2 * C_2[/tex]

    [tex]n[/tex] = number of mol
    [tex]V[/tex] = Volume in [tex]dm^3[/tex] ([tex]V_1[/tex] = Volume before, [tex]V_2[/tex] = Volume after)
    [tex]C[/tex] = Concentration in [tex]mol/dm^3[/tex] ([tex]C_1[/tex] = Concentration before, [tex]C_2[/tex] = Concentration after)

    Here are two examples of the usage of these formulae:

    I have 10 grams of table salt in 1 [tex]dm^3[/tex] water. If I increase the volume to 2 [tex]dm^3[/tex] what concentration will the final mixture have?

    [tex]m_(NaCl)[/tex] = 10 g
    [tex]V_1[/tex] = 1 [tex]dm^3[/tex]
    [tex]V_2[/tex] = 2 [tex]dm^3[/tex]

    [tex]M_(NaCl)[/tex] = 11 + 17 = 28 g/mol
    [tex]n_(NaCl)[/tex] = 10/28 mol
    [tex]C_(NaCl)[/tex] = (10/28)/1 = 10/28

    [tex]V_1 * C_1[/tex] = [tex]V_2 * C_2[/tex] =>

    [tex]C_2[/tex] = [tex]V_1 * C_1/V_2[/tex] = [tex]1 * (10/28) / 2[/tex] = 0.17....[tex]mol/dm^3[/tex]
     
    Last edited: May 27, 2006
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