Ap Chem Lab Help: Unknown Sulfate Salt And Have To Find The Mass %?

this is for an AP prep question and says i have an unknown sulfate salt and aqueus BaCl2. The BaS is insoluble so will percipitate out. you then can filter out the percipitate and find the mass of it. how do you go from having the mass of BaS produced to originol mass percent that sulfur is in the salt? I am sorry about my spelling i know its horrible.

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One Response to “Ap Chem Lab Help: Unknown Sulfate Salt And Have To Find The Mass %?”

  1. I’m a little confused by your question. I don’t think that barrium sulfide (BaS) will be precipitating out of your solution. It’s much more likely to be barrium sulfate (BaSO4).
    Assuming that you’re looking for the % mass of sulfur by looking at how much BaSO4 you have, here’s what to do:
    Take your mass of BaSO4 and convert to moles (by dividing by molar mass).
    Determine the number of moles of sulfate based on the number of moles of barium sulfate (1:1 mole ratio, so should be same #).
    Now, determine the number of moles of S from number of moles of SO4^2-. (1 mole of S in every mole of sulfate, so 1:1 mole ratio, so should be same # again)
    You now have the moles of sulfur in you barium sulfate salt. All of the sulfate in barium sulfate must have come from you original unknown sulfate salt. That also means that all of the moles of S must have come from that original moles of sulfate.
    Ok, so now you know the moles of S. Convert this to grams (multiply by molar mass). This is the mass of S in your original sample.
    Now divide the mass of S by the total sample mass and multiply by 100 to get your % mass of S in unknown sulfate salt.