Question

4 please

3. When titrating 25.0 mL of 0.10 M H;SO4 with 0.10 M NaOH, how many mL of NAOH will you have added to reach the first equivalence point? How many mL of NaOH will you have added to reach the second equivalence point? Show calculations. (4 pts) 4. A student completes a titration of an unknown diprotic acid. In their experiment, 0.79 g of the acid was dissolved in 250.0 mL of DI water. It required 13.48 mL of 1.0 M NaOH to reach the second equivalence point. What is the molar mass of the acid? Looking at the list of possible unknowns, what is likely to be the identity of the compound? Show calculations. (4pts)

Answer 1

Q4. Let the diprotic acid be H₂A

The balanced reaction is : H₂A (aq) + 2 NaOH (aq) $\rightarrow$ Na₂A (aq) + 2 H₂O (l)

concentration NaOH = 1.0 M

volume NaOH = 13.48 mL = 0.01348 L

moles NaOH added = (concentration NaOH) * (volume NaOH)

moles NaOH added = (1.0 M) * (0.01348 L)

moles NaOH added = 0.01348 mol

moles H₂A present = (moles NaOH added) * (1 mole H₂A / 2 moles NaOH)

moles H₂A present = (0.01348 mol) * (1/2)

moles H₂A present = (0.01348 mol) * (0.5)

moles H₂A present = 0.00674 mol

molar mass of acid = (mass of acid) / (moles of acid)

molar mass of acid = (0.79 g) / (0.00674 mol)

molar mass of acid = 117.2 g/mol

Unknown acid can be maleic acid H₂C₄H₂O₄ (molar mass 116 g/mol)