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chemistry

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1.) How much ethanol, C2H5OH, in liters (d=0.789g/ml) must be dissolved in water to produce 190.5 of 1.65 M C2H5OH? (Molarity problem.)


2.) How much concentrated hydrochloric acid solution (36.0% HCl by mass, d = 1.18g/mL}), in milliliters, is required to produce 11.0 L of 0.296 M HCl?

  • chemistry -

    1.) How much ethanol, C2H5OH, in liters (d=0.789g/ml) must be dissolved in water to produce 190.5 of 1.65 M C2H5OH? (Molarity problem.)

    190.5 WHAT for crying out loud?barrels, freight cars, lakes, I will assume you meant mL. If not that, adjust values below to what you should have written.
    M = moles/L and moles = grams/molar mass.

    1.65M = moles/0.1905. Calculate moles.
    moles = gram/molar mass.
    You know moles and molar mass, calculate grams.
    From the density, calculate volume of ethanol to use and convert to liters.

  • chemistry -

    molarity=mass/molmass*volumeinLiters

    1) massEthanol=density*volumeEthanol

    so volumeEthanol=molarity*molmass*Volumesolution/density

    Watch units.

    2)work out the similar steps for the HCL.

  • chemistry -

    2.) How much concentrated hydrochloric acid solution (36.0% HCl by mass, d = 1.18g/mL}), in milliliters, is required to produce 11.0 L of 0.296 M HCl?

    First calculate the molarity of the concentrated HCl.
    1.18 g/mL x 1000 mL - mass of 1 L = 1180 g.
    How much of that is HCl? 36% so,
    1180 x 0.36 = 424.8 g HCl.
    How many moles is that?
    424.8/36.5 = 11.6 M
    Now use the dilution formula to determine what you want to prepare.
    mL x M = mL x M
    Check my work. I estimated the molar masses and rounded here and there so you need to go through the problem yourself and do those numbers right.

  • chemistry -

    The second one is correct. Regarding the first one though, I calculated the grams to 6.8 g of C2H5OH. I don't quite understand the next step (regarding the density, etc)

  • chemistry -

    that was me who posted the comment above. my friend had the same question.

  • chemistry -

    I don't know how you obtained 6.8 g.
    The part about the density:
    The problem asks for VOLUME of ethanol to add to make ?? soln of ??M.
    mass = volume x density
    You calculate mass from above, substitute density here of 0.789, and solve for volume (in mL). Then convert to L. Look at your math. I don't get 6.18 grams (more like 15 g or so--in round numbers).

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