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CHEMISTRY

My chem class just finished a lab in which the objective was to find the percentage of silver and barium in a nitrate salt mixture by precipitating the chromates, separating out the precipitate from the solvent and spectator ions via filtration, and analysis of the combined precipitate.

In the lab the salt was dissolved and the barium and silver ions were precipitated with excess potassium chromate solution. the precipitate was collected.

i am supposed to find the percentage of silver and barium in the original sample; however i am having a VERY difficult time calculating this.

my teacher suggested either using a system of equations (two unknown variables) or finding the moles and then working from there. but i am really lost.

here is the data:
30mL of K2CrO4 @ .25 M
mass of flask: 95.383g
mass of flask & sample: 96.336g

after the precipate was collected and dried it weighed 0.944 g

any help setting up the calculation is much appreciated. if i didn't explain it well enough i woudl be happy to elaborate. i'm just really struggling right now.

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Catie

  1. Let X = mass Ag
    Let Y = mass Ba
    ========================
    One equation you can use is:
    X(molar mass Ag2CrO4/2*atomic mass Ag) + Y(molar mass BaCrO4/atomic mass Ba) = 0.944
    Do you have the mass of the sample of nitrates you used? I hope so. Then the second equation would be as follows:
    X(molar mass AgNO3/atomic mass Ag) + Y(molar mass Ba(NO3)2/atomic mass Ba) = mass sample taken.
    When you find X and Y, then
    % follows from that. Let me know if you still have problems.

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    DrBob222

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