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Effectiveness of makeshift titration setup

  1. Apr 17, 2012 #1
    Hello, I have to preform a titration on a alkali substance but do not have the neccesary equipment to do so. I was hoping a strip of litmus paper submerged in the solution could be used as an indicator and a small plastic syringe could be used instead of a buret. The exact concentration does not have to be known, just a simple percentage, so im not looking for anything fancy. Let me know if this will work and if there are other methods that will work better but do not use expensive equipment.
     
  2. jcsd
  3. Apr 17, 2012 #2

    Borek

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    Staff: Mentor

    Never tried it, but I don't see why it shouldn't work within a few percent error.

    How are you going to standardize your titrant?
     
  4. Apr 17, 2012 #3
    Well, I was going to use some 32 percent hydrochloric acid as a titrant. I'm thinking of diluting it to something like .005 mole per ml for easy calculations.
     
  5. Apr 18, 2012 #4

    Borek

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    Staff: Mentor

    As I wrote - I don't see why it shouldn't work in principle, although accuracy would be low. Comparing two samples - that one contains more base. this one contains less - should work OK.

    You may try red cabbage juice for an indicator.
     
  6. Apr 22, 2012 #5
    I often do simple titrations with a plastic eyedropper that has a 1.0 ml marking, and a pH indicator solution used for swimming pools (Phenol Red, Yellow to red pH 6.5-8.0), Aquarium test kits can also be obtained that will have similar indicator if there is a alkalinity test. The red cabbage juice also works, though the back titration from alkaline to acid has be slow since the bluish form tends to precipitate and has to be redissolved during back titration with standard acid.

    I make my acid (from simple muratic acid from the hardware store) about 100+-50 millimolar, and make a caustic solution from aq 45% KOH to be approximately the same millimolarity.
    I standardize against an aliquot of "distilled white vinegar" (not distilled but made from distilled alcohol -Wiki has this mistaken at least here in the US). This is mandated in the US to be not less than 5% by volume acetic acid, and I use a drop counting method to get my factors for drops per ml titrant (typically about 30-32 drops per ml). I use a forward titration with unstandardized base and the Phenol red to a stable just beginning pinkish orange, note the number, and overtitrate to red. I find that economics would suggest that the manufacturer won't sell vinegar that exceeds the minimum by even two sig figs (vinegar is made concentrated at about 8-12% from microbial oxidation of spirits and nutrient according to Othmer's Chemical Processes, and diluted to standards for sale) so it makes a good standard that can be calculated after converting the aliqot to the number of millimole acetic acid. After overshooting , I then use the vinegar to back titrate, and record the amounts. A titration that involves about 60 drops titrant will give a figure that is good to two sig figs. The HCL is then titrated against the standardized base, and can be used for back titrations.

    In this way I have been able to monitor and adjust pH for feedstocks (syrups, hydrolyzates, etc..) used for biofuel fermentations. The processes scale up and can be monitored cheaply, and Phenol red can be readily seen even with some brownish starting materials.

    I keep the caustic titrant in a closed bottle to prevent reaction with CO2, and will re-standardize weekly.
     
    Last edited: Apr 22, 2012
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