# Chemical Forums

## Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: jbarradas on July 14, 2007, 02:49:28 PM

Title: pH of NaHCO3 solution why Ph=8 ???
Post by: jbarradas 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
Title: Re: pH of NaHCO3 solution why Ph=8 ???
Post by: Yggdrasil on July 15, 2007, 05:38:32 AM
You also have this equilibrium:

HCO3- <--> H+ + CO32-
Title: Re: pH of NaHCO3 solution why Ph=8 ???
Post by: Borek on July 15, 2007, 12:09:07 PM
http://www.chembuddy.com/?left=pH-calculation&right=pH-amphiprotic-salt
Title: Re: pH of NaHCO3 solution why Ph=8 ???
Post by: the17train 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
Title: Re: pH of NaHCO3 solution why Ph=8 ???
Post by: AWK on July 27, 2007, 01:27:26 AM
pH=-log(SQRT(K1xK2) = 8.34 in this case, practically pH only slightly depends on concetration