Question

An analytical chemist weighs out 0.026 g of an unknown triprotic acid into a 250 mL volumetric flask and dilutes to the mark with distilled water. She then titrates this solution with 0.0800 M NaOH solution. When the titration reaches the equivalence point, the chemist finds she has added 9.9 mL of NaOH solution Calculate the molar mass of the unknown acid. Be sure your answer has the correct number of significant digits. mol

Answer 1

let us asume that triprotic acid as HX Equation: H3+ 3NaOH > Na,X3H2O 1L No of moles of NaOH 9.9 mL x, 0.0800 mol X 1000 mL L 0.000792 mol 1 mol H2X No of moles of triprotic acid(H,X) = 0.000792 mol NaOH x- 3 mol NaOH 0.000264mol HX 0.026 g Molar mass of the triprotic acid(H3X 0.000264 mol 98.48 g/mol 98 g/mol