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Math Help - math water problem

  1. #1
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    math water problem

    "you have a 55 gallon fish tank, which you want to keep at 34.5 ppt. How many kg of sea-salt should you add?"

    I can't figure this problem out and any help anyone could give would be much appreciated. thanks.


    also, there is a follow up question associated with this: "if 3 gallons of water evaporate from the tank, what is the salinity now?"
    Last edited by willowthewisp; August 31st 2012 at 07:57 AM.
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  2. #2
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    Re: math water problem

    Well, it's strange that the problem mixes gallons and kg, liters would be nicer. I'm guessing a mass fraction ratio for the problem (mass of salt:mass of water)?

    55 gallons converts to 208 litres of water, which means 208 kg of water.

    therefore: 208 kg * 34.5 * 10^-12 parts ~= 0.000000007176 kg of salt. (7.18 * 10^-9 kg)

    then for the follow up you do the mass of salt divided by the new mass of water, 52 gallons -> 197 kg

    7.18 * 10^-9 kg / 197kg = 3.64 *10^-11 -> 36.4 parts per trillion

    hope this helps.
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  3. #3
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    Re: math water problem

    thanks very much. this was helpful.
    Last edited by willowthewisp; September 1st 2012 at 05:55 AM.
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