Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: jbarradas on July 14, 2007, 02:49:28 PM
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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
please anyone could help me?
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You also have this equilibrium:
HCO3- <--> H+ + CO32-
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http://www.chembuddy.com/?left=pH-calculation&right=pH-amphiprotic-salt
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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
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pH=-log(SQRT(K1xK2) = 8.34 in this case, practically pH only slightly depends on concetration