# Thread: ACID + BASE equations...and H+ concentrations.

1. ## ACID + BASE equations...and H+ concentrations.

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?

2. ## Re: ACID + BASE equations...and H+ concentrations.

Originally Posted by 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?
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.

3. ## Re: ACID + BASE equations...and H+ concentrations.

Originally Posted by InteGrand
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.

4. ## Re: ACID + BASE equations...and H+ concentrations.

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.

There are currently 1 users browsing this thread. (0 members and 1 guests)

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•