You can use M x V = M' x V'
3 x V = 250 x 1.2
V = 100 ml
The molarity of formic acid is 100 mM or . The dissociation reaction of formic acid is as follows:
The expression for dissociation constant of the reaction will be:
Rearranging,
Here, pH of solution is 4.15 thus, concentration of hydrogen ion will be:
Similarly, thus,
Putting the values,
Therefore, the concentration of formate will be 0.2511 M.
Number of moles = number of atoms/Avogadro's number
= (4.8x10^25)/(6.02x10^23)
=79.7 mol (3sf)