Chemistry

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How much 5M KOH must be added to 1.0 L of 0.1M glycine (pKa 9.6) at pH 9.0 to bring its pH to exactly 10.0?

  • Chemistry -

    Use the Henderson Hasselbalch equation twice.

    First set of conditions:
    pH=9.0
    pka=9.6

    Solve for the ratio
    pH=pka+log[A-/HA]

    9.0=9.6+log[A-/HA]
    10^(9.0-9.6)=[A-/HA]
    0.25=[A-/HA]

    Meaning 25% of the solution is protanated, or 0.025 moles is A- and 0.075 moles HA

    Second set of conditions
    pH=10.0
    pka=9.6

    Solve for the ratio
    pH=pka+log[A-/HA]

    10=9.6+log[A-/HA]
    10^(10.0-9.6)=[A-/HA]
    25.0=[A-/HA]

    Meaning 25% of the solution is deprotanated, or 0.025 moles is HA and 0.075 moles A-

    I need to go from 0.025 moles of A- to 0.075 moles of A-, and I need to go from 0.075 moles of HA to 0.025 moles of HA. This means that I need 0.05 moles of KOH.

    5M KOH=0.05 moles of KOH/L

    Solve for volume,

    0.05 moles of KOH/5M=L of KOH

  • Chemistry -

    Typos---

    Change 0.025 to 0.25
    change 0.075 to 0.75
    change 0.05 to 0.5

    Everything is correct.

  • Chemistry -

    Never mind, I was correct the first time.

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