ACID + BASE equations...and H+ concentrations. (1 Viewer)

[Mr_Kap]

Equal volumes of equimolar solutions:
H₃PO₄ + NaOH --> NaH₂PO₄(aq) + H₂O

As the relative amount of OH- increases, you could get
H₃PO₄ + 2NaOH --> Na₂HPO₄(aq) + 2H₂O

And with a substantial excess of NaOH, then you get
H₃PO₄ + 3NaOH --> Na₃PO₄(aq) + 3H₂O

Do we need to know all three? Or just the last one.


Also, for monoprotic acids (like HCL), the concentration of it is the same as the H+ concentrations.
If you had a triprotic acid (like H₃PO₄), at concentration 0.1 mol/L, how do I find the H+ concetration? Is it possible?

 

[InteGrand]

Equal volumes of equimolar solutions:
H₃PO₄ + NaOH --> NaH₂PO₄(aq) + H₂O

As the relative amount of OH- increases, you could get
H₃PO₄ + 2NaOH --> Na₂HPO₄(aq) + 2H₂O

And with a substantial excess of NaOH, then you get
H₃PO₄ + 3NaOH --> Na₃PO₄(aq) + 3H₂O

Do we need to know all three? Or just the last one.


Also, for monoprotic acids (like HCL), the concentration of it is the same as the H+ concentrations.
If you had a triprotic acid (like H₃PO₄), at concentration 0.1 mol/L, how do I find the H+ concetration? Is it possible?

For HSC, you don't need to calculate numerical values for polyprotic acids, since the latter stages don't dissociate 100%. For things like H₂SO₄ (diprotic), if they do ask you to calculate, you'd just assume that 2 H⁺ ions result from each H₂SO₄ molecule (even though in reality it's something like 1.8).

And if you have a good memory, best to memorise all the equations. I can't remember whether they are all needed or not.

 

[Mr_Kap]

For HSC, you don't need to calculate numerical values for polyprotic acids, since the latter stages don't dissociate 100%. For things like H₂SO₄ (diprotic), if they do ask you to calculate, you'd just assume that 2 H⁺ ions result from each H₂SO₄ molecule (even though in reality it's something like 1.8).

And if you have a good memory, best to memorise all the equations. I can't remember whether they are all needed or not.

Ok. Thx.

 

[MaccaFacta]

Polyprotic acid equations also apply to buffer solutions (9.2.4.2.9). Blood contains three buffers (bicarbonate, hydrogen phosphate and haemoglobin). The bicarbonate buffer being the most important. I would suggest learning all of the equations associate with the CO2 / bicarbonate buffer, and also learning the three equations for the phosphate.