thank you! the first part is correct. mL Reset The flask shown here contains 0.5

Question

thank you!

the first part is correct.

mL Reset The flask shown here contains 0.501 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.310 M NaOH 10 15 20 25 30 35 40 45 20 25 30 What volume of base is needed to reach the end point of the titration? Number 25 mL base 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

H2A + 2NaOH -------------------> Na2A + 2H2O

1 mole    2 moles

volume of NaOH    = 25ml

molarity of NaOH = 0.31M

no of moles of NaOH = molarity * volume in L

                                       = 0.31*0.025   = 0.00775moles

2 moles of NaOH react with 1 moles of H2A (acid)

0.00775moles of NaOH react with = 1*0.00775/2   = 0.003875moles of H2A

molar mass of acid     = mass of acid/no of moles of acid

                                   = 0.501/0.003875    = 129.3g/mole

                                                         

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