Given:
Volume of sample = 5 mL Borax (Sodium tetraborate)
Temperature = 49.5 degrees C
Volume of titrant = 18.23 mL
Concentration of Titrant = 0.2222 M HCl
First, set-up a balanced equation:
Na2B4O7*10H2O(borax) + 2 HCl = 2 NaCl + 4 H3BO3 + 5 H2O
Calculate the concentrations of HCl, NaCl, and H3BO3, then solve for the Ksp or Solubility Product Constant:
Ksp = ([NaCl]^2 * [H3BO3]^4) / [HCl]^2