Question

167 mL of 4.7 M HBr solution is mixed with 176 mL of NaOH solution of unknown concentration. The H+ concentration in the final solution is 0.09M. What was the NaOH concentration of the unknown solution?

Answer 1

The balanced equation is HBr + NaOH ---------> NaBr + H20 1 mole of HBr reacts with 1mole of NaOH Number of moles of HBr = 4.7 M * 167 mL = 784.9 mmol Let M be the molarity of NaOH Number of moles of NaOH = M* 176 mL = 176M mmol Net moles of H+ = 784.9 - 176M Total volume = 167 + 176 = 343 mL Given that Number of moles of HBr remaining in the solution = 0.09 M* 343 mL = 30.87 mmol So, 784.9 - 176M = 30.87 176 M = 784.9-30.87 176M = 754.03 M = 4.284261 M Molarity of NaOH solution = 4.28 M