The flask shown here contains 0.0820 g of acid and a few drops of phenolphthalei

Question

The flask shown here contains 0.0820 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.130 M NaOH. What volume of base is needed to reach the end point of the titration? Assuming the acid is monoprotic, what is its molar mass? You may not have reached the end point of the titration yet, or you may be reading the volume in the buret incorrectly. Be sure to read the liquid level at the bottom of the meniscus. Once you see pink that fades away in the flask, continue adding base drop by drop until the pink color persists in the flask.

Explanation / Answer

Volume of NaOH from the diagram = 10ml

NaOH + HA -----------> NaA + H2O

1 mole 1 mole

no of moles of NaOH = molarity * volume in L

                                  = 0.13*0.01 = 0.0013moles

from the balanced equation

1mole of NaOH react with 1 mole of HCl

1.3 mole of NaOH react with 1.3 mole of HCl

molar mass of HA = mass of HA/no of moles of HA

                              = 0.082/0.0013   = 63g/mole

                                          

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