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### Topic: pH of NaHCO3 solution why Ph=8 ???  (Read 34196 times)

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##### pH of NaHCO3 solution why Ph=8 ???
« on: July 14, 2007, 02:49:28 PM »
NaHCO3---> Na+   +    HCO3-

HCO3- H+---> H2CO3

so Ka H2CO3=4,2*10^-7

so[HCO3-]*[H+]/H2CO3 = 4,2*10^-7

thats why 0,1M NaHCO3 should make pH=12,3... but its only 8,1

I can not understand what I am missing
« Last Edit: July 14, 2007, 07:21:49 PM by jbarradas »

#### Yggdrasil

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##### Re: pH of NaHCO3 solution why Ph=8 ???
« Reply #1 on: July 15, 2007, 05:38:32 AM »
You also have this equilibrium:

HCO3- <--> H+ + CO32-

#### Borek

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##### Re: pH of NaHCO3 solution why Ph=8 ???
« Reply #2 on: July 15, 2007, 12:09:07 PM »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### the17train

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##### Re: pH of NaHCO3 solution why Ph=8 ???
« Reply #3 on: July 26, 2007, 05:47:56 PM »
Where did 12.3 come from? I'm getting 10.3 when using Ka=4.3*10^-7.
Ka=[OH-][H2CO3]/[HCO3-]=     x^2/(.1)
Therefore x=[OH-]=.000207
pOH=-log(.000207)
14-3.6833=10.32
pH=10.32

#### AWK

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##### Re: pH of NaHCO3 solution why Ph=8 ???
« Reply #4 on: July 27, 2007, 01:27:26 AM »
pH=-log(SQRT(K1xK2) = 8.34 in this case, practically pH only slightly depends on concetration
AWK