March 29, 2024, 01:42:46 AM
Forum Rules: Read This Before Posting


Topic: Why can CaCO3 precipitate by utilizing bicarbonate?  (Read 1096 times)

0 Members and 1 Guest are viewing this topic.

Offline Uwe

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
Why can CaCO3 precipitate by utilizing bicarbonate?
« on: October 13, 2020, 08:24:17 PM »
It is sometimes stated that CaCO3 precipitation in seawater can occur either following

(1) Ca2+ + Co32- -> CaCO3


or

(2) Ca2+ + HCO32- -> CaCO3 + H+

In an abiotic system, in which CaCO3 precipitation only follows thermodynamics, why would CaCO3 precipitation follow equation 2?

It is sometime stated that this would occur as DIC at a the pH range of seawater is mainly composed of HCO32-. But the CaCO3 lattice is composed of Ca2+ and carbonate, not bicarbonate ions, so ultimately the precipitation reaction will again be equation 1

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Why can CaCO3 precipitate by utilizing bicarbonate?
« Reply #1 on: October 14, 2020, 03:04:05 AM »
Think about it this way: first equation refers to the overall process consisting of a dissociation followed by the precipitation.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links