Sapling Learning macmillan learning The flask shown here contains 0.648 g of aci

Question

Sapling Learning macmillan learning The flask shown here contains 0.648 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.160 M NaOH. What volume of base is needed to reach the end point of the titration? Number 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? Number g mol mL. 15 20 25 30 35 40 45 50 Map Reset 10 15 Add base to the solution until it just turns pink. You may need to reset the titration if you go past the end point.

Explanation / Answer

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

from diagram volume of NaOH = 10ml

no of moles of NaOH = molarity * volume in L

                                    = 0.16 *0.01 = 0.0016moles

from balanced equation

1 mole of acid react with 2 moles of NaOH

2 moles of NaOH react with 1 moles of H2A

0.0016moles of NaOH react with = 0.0016*1/2 = 0.0008moles of H2A

molar mass of H2A = mass of acid/ no of moles of Acid

                                = 0.648/0.0008   = 810g/mole

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