Question

Order these chemical species by increasing pH of an 0.1M aqueous solution of each. That is, imagine making an 0.1M solution of each species. Select 1 next to the species that makes the solution with the lowest pH. Select 2 next to the species that makes the solution with the next higher pH, and so on. Notice that some of the rankings have been filled in for you already. Also notice that water is on the list. For that particular case, just compare the pH of pure water to the pH of the other solutions. Note for advanced students: for all charged species, you may assume the necessary counterions act as neither acids nor bases. species relative pH of 0.1M aqueous solution H2C2O4 ▼1 (lowest) H3O+ ▼(Choose one) H3PO4 4 HIO3 2 IO3− ▼(Choose one) HC2O4− 7 H2O 5 H2PO4− ▼(Choose one)

Answer 1

The increasing order of pH is: HIO3 < H3O+< H2C2O4 < H3PO4 <HC2O4-<H2PO4- < IO3- < H2O

For weak acid pH is calculated by the formula:

For weak bases:

Formulation:

If degree of dissociation of weak acid HA

and C= initial concentration of weak acid

Equilibrium Concentration of H, [H+] =

From Ostwald dilution principle,

Therefore,

Now, for H2C2O4,

for H3PO4,

for HIO3,

for IO3-, (a conjugate base)

for HC2O4-, (pKa = 4.27)

for H2PO4-, (pKa ​​​​​​​= 7.2)

These were all weak acids or their conjugate bases. [Note how the conjugate bases have higher pH because they are well bases!]

for H2O, (Duh!)

Water has the equilibrium going for it producing exactly equal amounts of H+ and OH- making it neutral.

for H3O+,

Since H3O+ is a strong acid, it will be totally dissociated. Actually H+ is present in water as H3O+. SO, the concentration of H+ is same as that of H3O+.