chemistry

A 2.118 g sample of a solid mixture containing only potassium carbonate ( MM=138.2058 g/mol ) and potassium bicarbonate ( MM=100.1154 g/mol ) is dissolved in distilled water. A volume of 30.20 mL of a 0.763 M HCl standard solution is required to titrate the mixture to a bromocresol green end point. Calculate the weight percent of potassium carbonate and potassium bicarbonate in the mixture.

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  1. The HCl reacts completely with both as follows:
    K2CO3 + 2HCl ==> 2KCl + H2O + CO2
    KHCO3 + HCl ==> KCl + H2O + CO2
    You set up two equations and solve them simultaneously.
    Let x = grams K2CO3
    and y = grams KHCO3.
    eqn 1 is x + y = 2.118
    --------------------------------------
    eqn 2 comes from
    mols HCl to titrate K2CO3 + mols HCl to titrate KHCO3 = mols HCl used.
    (2x/MM K2CO3) + (y/MM KHCO3) = mols HCl x L HCl

    Solve these two equations simultaneously. When you get x and y then
    % K2CO3 = (g K2CO3/wt sample)*100 = ?
    % KHCO3 = (g KHCO3/wt sample)*100 = ?
    Post your work if you get stuck.

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    DrBob222
  2. @DrBob222
    I am stuck,
    x=1.590 g of k2CO3=> x+y=2.118
    1.590+y=2.118 => y=0.528 g of KHCO3
    then 0.528 g to moles
    2x+0.00527 mole=0.0230 mol => x=1.225 g of KCO3

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