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  • Dilution Calculator

    I am having a brain fart. I have a solution that is 37% formaldehyde, and 63% (inert ingredient). I wish to further dilute this solution to 10% formaldehyde. The simple answer in my mind is that one gallon presently would make 3.7 gallons at 10%, but I'm not sure. Besides, I want to do this about 8 ounces, 10% at a time. Could someone walk me through a simple calculation please.
    Arbo & Thor (The Junkyard Dog)

  • #2
    Originally posted by arbo View Post
    i am having a brain fart. I have a solution that is 37% formaldehyde, and 63% (inert ingredient). I wish to further dilute this solution to 10% formaldehyde. The simple answer in my mind is that one gallon presently would make 3.7 gallons at 10%, but i'm not sure. Besides, i want to do this about 8 ounces, 10% at a time. Could someone walk me through a simple calculation please.
    v1*c1 = v2*c2

    1*37 = v2*10

    37 / 10 = v2

    v2 = 3.7

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    • #3
      Originally posted by snowman View Post
      v1*c1 = v2*c2

      1*37 = v2*10

      37 / 10 = v2

      v2 = 3.7
      In case the gasses haven't dissipated yet, that's original solution volume (v1) times original solution concentration (c1) is proportional to (=) the secondary solution volume (v2) times the secondary solution concentration (c2). Units don't matter.

      An easier to get to where you want to be would be {sort of} new desired quantity (q1) times new desired concentration (c1) requires (=) quantity of original solution (q2) times the original solution concentration (c2). Again units don't matter as long as q1 and q2 are the same units - ounces, grams, gallons, etc.

      So:

      To get {sort of} 8 ounces of 10% concentration -

      q2 * c2 = q1 * c1

      q2 * .37 = 8 * .1

      q2 * .37 = .8

      q2 = .8 / .37

      q2 = 2.16.........

      Adding 2.16 oz of original concentration (37%) to 8 ounces of [inert] would yield 10.16 ounces of 10% solution. That's why I said sort of. Yes, you can perform the calculations to determine both quantities so as to yield exactly 8 ounces, but you said you wanted easy.
      Kevin

      More tools than sense.

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      • #4
        Simply...

        37% original is 37 parts formaldehyde plus 63 parts inert in 100 parts total

        10% solution is 37 parts formaldehyde in 370 parts total

        So must add 270 parts inert to 100 parts original to make 370 parts of 10%, as per OP.


        To make 8oz of 10%, add :-

        100/370 * 8oz original = 2.16 oz

        270/370 * 8oz inert = 5.84 oz


        Cheers

        .

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        • #5
          Originally posted by KJ1I View Post
          but you said you wanted easy.
          Easy you said? Go to wolframalpha.com (the guys who wrote mathematica) and type in

          8 * 0.10 = x * 0.37

          scroll down to find x = 2.16216. So dump 2.16216 ounces in 8 ounce cup and dilute to 8 oz and your good.

          You want 8 oz total at 10% concentration. So you want the total amount of "stuff" as 10% of 8 (in 8 of water). Now the stuff is currently 37% so an ounce has 37%*(x ounces) as you pour it into the little container.

          So 8 * 0.10 (aka 10%) = x * 0.37 (aka 37%) Both sides are the "actual amount of dissolved stuff you want" one measured as the finished product and one as the higher conc stuff.

          The biggest problem is remembering theres 128 ounces in a gallon. Or so google says. Metric would certainly be easier. I think 8oz is an old fashioned "cup". Before "cup" meaning was changed to two quart size "big gulp" of corn syrup soda except in NYC but I digress.

          There are engineering problems here. First of all you don't have 37%. That stuff (essentially) evaporates over time. You probably have somewhere over 35% but I guarantee they didn't ship anything more expensive than 37% to you. Unless you took quantitative chemical analysis class at uni like I did and you just tested it to get 37.0000000%... Also you don't have gear to measure to better than 1 or 2 sig figs anyway.

          The engineering way to do it is you've got stuff thats around four times too strong. To one sig fig or so, fill the bucket or whatever to about a quarter full and then fill to brim with water.

          A better question is why you're screwing around with formaldehyde. You're talking about measuring ounces worth of 37% and an ounce or so of that concentration will kill you if swallowed. Also its a known carcinogen aka you're gonna either die sooner or later. I hope you're not trying to preserve coolant with it; it'll work great, but in civilized areas its highly illegal because of the above kill you now or later thing. Civilized areas aka I know for a fact its highly illegal in .eu but not so sure about .us. As far as breathing the fumes you need to keep it in the single digit ppb (yes ppb not ppm) range to stay legal although WRT to "staying legal" being good enough, well, good luck suing a cancer cell if it starts growing "illegally", you're still gonna die anyway. If you work out the math for ppb and fooling around with ounces at a time, you need a pretty stiff wind and god help anyone living downwind (or you, when/if they sue you)

          There's no such thing as perfectly safe or perfectly dangerous. I'd rank this stuff as way worse than gasoline, probably around but a little worse than the exotic paints that folks wear space suits in, but not nearly as bad as some pesticide/nerve agents or organometallics. In other words if you try really hard you can find something more dangerous, but its gonna be difficult. In the lab I would not have screwed around with this stuff outside a hood and I'd wear gloves, but I'm hardly the ideal of lab safety.

          The good news about formaldehyde is if it doesn't outright kill you or kick off a lovely cancer, its pretty harmless in that it doesn't bioaccumulate like lead and stuff like that. You'll pee it right out (aka drinking lots of clean water before and after handling it would probably be wise-ish just on general principles). One interesting factoid about formaldehyde is methanol is mostly harmless to the body, at least not much worse than ethanol, until its metabolized by your liver resulting in formaldehyde, which promptly kills you (hey your liver don't know no better, it thought it was helping...) So the symptoms of drinking methanol poisoning vaguely resemble the symptoms of formaldehyde poisoning. If you get poisoned and somehow avoid dying and end up in the ER they're certain to misdiagnose you as methanol poisoned rather than formaldehyde (hear hooves, think horse not zebra, etc). One labmate who was more paranoid than myself wrote in sharpie pen on his arm that he's been exposed to formaldehyde in the optimistic hope that if the 2nd to worst case scenario happens the ER docs would have a better idea whats up. Not saying you should get out the sharpie pen but ...

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