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Chemistry

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Find the pH of a buffer that consists of 0.82 M methylamin (CH3NH2) and 0.71 M CH3NH3Cl (pKb of methylamine (CH3NH2) = 3.35.)

I keep getting 3.41, but it says that it's wrong...

  • Chemistry -

    CH3NH2=0.71M=B
    CH3NH3Cl=0.82M=BH

    B+H2O--->BH +OH


    kb=[OH][BH]/{B}

    kb=[OH]*([BH]/[B])

    -logkb=-log[OH]*-log([BH]/[B])

    pkb=pOH-log([BH]/[B])

    pOH=pKb+log([BH]/[B]

    pH=14-pOH

  • Chemistry -

    Essentially, I was thinking this problem out by deriving the Henderson-Hasselbalch equation. You only need the following information to calculate your answer:

    CH3NH2=0.71M=B
    CH3NH3Cl=0.82M=BH


    pOH=pKb+log([BH]/[B]

    pH=14-pOH

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