Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: xshadow on October 04, 2020, 11:30:02 AM
-
Hi
If I have to calculate pH of Ca(OH)2 I get a basic pH...(using its Kps)
But I've stutied that a Ca2+ ion in a solution is coordinated by 6 (for example) molecules of water getting:
[Ca·(OH2)6]2+
Then my text says that this ""complex"" is acid and can loose H+ getting:
[Ca·(OH)6]4- + 6H+
But at this can it loose all the OH- ?
Because I've seen that Ca(OH)2 ----> Ca2+ + 2 OH-
Thanks!
-
It is true that Ca(OH)2 is a strong base.
It is also true that the hydrated calcium cation is a very weak acid, which means that it forms a very small amount of H3O+ ions in the aqueous solution.
What happens when you mix a small amount of weak acid with a large amount of strong base?
-
It is true that Ca(OH)2 is a strong base.
It is also true that the hydrated calcium cation is a very weak acid, which means that it forms a very small amount of H3O+ ions in the aqueous solution.
What happens when you mix a small amount of weak acid with a large amount of strong base?
It happens an acid-base reaction with a salt formation and a residual amount of strong (base) in excess that will give the pH
My doubt now is:
If I put Ca(OH)2 in water It dissociates forming Ca2+ ions
Now those Ca2+ ions will be coordinated by water molecule Ca(H2O)6 and it can lose H+
So is the same thing a Ca(OH)2 (the ionic compound) and a [Ca(OH)6]4-??
In the second one 6 -OH-coordinate the Ca2+ ion
While in the first case - Ca(OH)2- I think is a solid (ionic compound) with a different structure and ""bond type""
Thanks
-
There are many reactions that take place when you dissolve Ca(OH)2, but in the end what matters when calculating pH is _measured_ values of Ksp and/or Kb - they typically take everything into account. That's because we don't measure these values directly, we calculate them from measured equilibrium concentrations of ions involved, and they depend on all equilibria involved.
Sometimes it means the result is only approximate, but for most calculations it doesn't matter, there are many more sources of uncertainty, most of the more important.
-
There are many reactions that take place when you dissolve Ca(OH)2, but in the end what matters when calculating pH is _measured_ values of Ksp and/or Kb - they typically take everything into account. That's because we don't measure these values directly, we calculate them from measured equilibrium concentrations of ions involved, and they depend on all equilibria involved.
Sometimes it means the result is only approximate, but for most calculations it doesn't matter, there are many more sources of uncertainty, most of the more important.
so when I see its K equilibrium all these possible reactions are already considered
thanks!