Moles of NaOH required to make a buffer with a pH of 12.4 will be 1.18.
Calculation of moles:
1L of 1M solution of [tex]H_3PO_4[/tex]
Buffer pH= 12.4
As we know
pH + pOH= 14
pOH= 14 - pH
pOH= 14 - 12.4
pOH= 1.6
Also,
[tex]pOH= -log[OH^-]\\[/tex]
By calculating concentration of Hydroxide ion, we can calculate the moles of NaOH required.
[tex]1.6= -log[OH^-]\\[/tex]
Taking antilog, we get
[tex][OH^-]= 1.18M[/tex]
As the volume of the solution is 1L.
Molarity is number of moles of solute in 1L of the solution.
Therefore, moles of [tex][OH^-]= 1.18[/tex]
So, number of moles of NaOH required will be 1.18.
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