ml The flask shown here contains 0.724 g of acid and a few drops of phenolphthal

Question

ml The flask shown here contains 0.724 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.200 M NaOH 5 10 - 15 E20 25 30 E 35 40 45 What volume of base is needed to reach the end point of the titration? Number mL base Click to begin What is the molar mass of the acid (assuming it is diprotic and that the end point corresponds to the second equivalence point)? Add base to the solution until it just turns pink. You may need to reset the titration if you go past the end point. Number g/mol

Explanation / Answer

Solution :-

NaOH + HX ------> NaX + H2O

1 mole 1 mole

asume volume of NaOH at end point is 20ml

no of moles of NaOH = molarity * volume in L

                                 = 0.2*0.02 = 0.004 moles

From the balanced equation

no of moles of NaOH = no of moles of HX

0.004 moles             = no of moles of HX

no of moles = mass of HX/molar mass of HX

molar mass of HX(acid) = mass of Hx/no of moles of HX

                                   = 0.724/0.004 = 181g/mole

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