Question

Enthalpy and Entropy Changes for Borax Dissolution Lab? How would I calculate the concentration of a borate ion from the volume of 0.500 M HCl used in each titration. I
can post more information about the lab if needed. Please explain.

Answer 1

All borates can be considered derivatives of boric acid, B(OH)₃. Boric acid is a weak proton donor (pK_a ~ 9) in the sense of Brønsted acid, but is a Lewis acid, i.e., it can accept an electron pair. In water, it behaves as a Lewis acid accepting the electron pair of a hydroxyl ion produced by the water autoprotolysis.

So, B(OH)₃ is acidic because of its reaction with OH^– from water, forming the tetrahydroxyborate complex (B(OH)₄^–) and releasing the corresponding proton left by the water autoprotolysis

B(OH)4- + 4HCl -> B(Cl)4-

According to this rxn you can use:

Volume of acid used in titration till end point. Then calculate the moles. After that calculate the moles of borate. The divide them by the volume of borate sample in liters.