0.68g of a solid diprotic acid was dissolved in 30.0mL of a 0.50 NaOH sol'n. the resulting mixture was then back-titrated against 0.20 M HCl; 25mL were required. Calculate the molar mass of the acid. This acid is a solid salt of a triprotic acid, identify this acidic salt.

m/mm* n(H+) + [HCl] * Va*n(+)+) = [NaOH]*Vb*n(OH)

0.68g/mm*2 + [0.02M]*0.025L*1 = [0.5M]*0.03L*1
PO4=mol

I can't get the answer.

Can anyone help?

To calculate the molar mass of the acid and identify the acidic salt, we need to use the information given in the problem. Let's break down the steps:

Step 1: Determine the moles of NaOH used.
Given that the volume of the NaOH solution used is 30.0 mL and the concentration is 0.50 M, we can calculate the moles of NaOH by multiplying the volume (in L) by the concentration (in mol/L).

moles of NaOH = volume of NaOH (L) * concentration of NaOH (mol/L)
moles of NaOH = 30.0 mL * (1 L / 1000 mL) * 0.50 mol/L
moles of NaOH = 0.015 mol

Step 2: Determine the moles of HCl used.
The back-titration with HCl consumed 25 mL of 0.20 M HCl.

moles of HCl = volume of HCl (L) * concentration of HCl (mol/L)
moles of HCl = 25.0 mL * (1 L / 1000 mL) * 0.20 mol/L
moles of HCl = 0.005 mol

Step 3: Calculate the moles of the diprotic acid.
Since NaOH and HCl react in a 1:1 ratio, the moles of HCl used is equal to the moles of NaOH reacted.

moles of acid = moles of HCl = 0.005 mol

Step 4: Calculate the molar mass of the acid.
The molar mass of the acid can be calculated by dividing the mass of the acid by the moles of the acid.

mass of acid = 0.68 g
molar mass of the acid = mass of acid (g) / moles of acid

molar mass of the acid = 0.68 g / 0.005 mol
molar mass of the acid = 136 g/mol

The molar mass of the acid is 136 g/mol.

Step 5: Identify the acidic salt.
The problem states that the acid is a solid salt of a triprotic acid. Since we found the molar mass of the acid to be 136 g/mol, it matches with the molar mass of phosphoric acid (H3PO4). Therefore, the acidic salt is likely to be sodium phosphate (Na3PO4).

So, the molar mass of the acid is 136 g/mol, and the acidic salt is likely sodium phosphate (Na3PO4).