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In an experiment a student dissolves 0.138g of a triprotic acid in 100.00 mL of water...

In an experiment a student dissolves 0.138g of a triprotic acid in 100.00 mL of water to prepare a solution for titration. A 25.00mL aliquot of the acid solution reqiures 15.49 mL of .108 M NaOH solution to reach the equivalence point. Calculate the molar mass of acid.

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Expert Solution

No. of moles of solute = given mass / molar mass

molar mass = given mass / no. of moles of solute

So to calculate molar mass first you need to calculate no. of moles of acis & for that you need to calculate molarity of an acid.

by apply molarity equation: M1V1      =      M2V2

                                         NaOH     =      acid                M1 = 0.108 M   , V1 = 15.49 ml   ,M2 = ?     V2 = 25.00ml

                                     0.108 M . 15.49 ml = M2 . 25.00 ml

                                     0.108 M . 15.49 ml / 25.00 ml   = M2

                                    molarity of acid , M2 = 0.067 M

             Molarity = no. of moles of solute / 0.1 L of solvent . ----- (i)     (100 ml = 0.1 L )

           no. of moles of solute     = molarity * volume

   = 0.067 * 0.1

   = 0.0067

   no. of moles of solute = given mass / molar mass

0.0067 = 0.138 / molar mass

molar mass = 0.138 / 0.0067

   molar mass of an acid = 20.59 g                                 

queen_honey_blossom answered 2 years ago
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