November 21, 2024, 12:15:07 PM
Forum Rules: Read This Before Posting


« previous next »
Pages: [1]   Go Down

Topic: pH of NaHCO3 solution why Ph=8 ???  (Read 35376 times)

0 Members and 1 Guest are viewing this topic.

Offline jbarradas

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
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
please anyone could help me?
« Last Edit: July 14, 2007, 07:21:49 PM by jbarradas »
Logged

Offline Yggdrasil

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 3215
  • Mole Snacks: +485/-21
  • Gender: Male
  • Physical Biochemist
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-
Logged

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27852
  • Mole Snacks: +1813/-412
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: pH of NaHCO3 solution why Ph=8 ???
« Reply #2 on: July 15, 2007, 12:09:07 PM »
Logged
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline the17train

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
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
Logged

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7976
  • Mole Snacks: +555/-93
  • Gender: Male
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
Logged
AWK
Pages: [1]   Go Up
« previous next »
Sponsored Links