#9 First answer is correct, second is not. Correct answer is most important, but
ID: 958249 • Letter: #
Question
#9 First answer is correct, second is not. Correct answer is most important, but feel free to show work. Thanks!
mL Reset The flask shown here contains 0.556 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.150 M NaOH 20 25 30 What volume of base is needed to reach the end point of the titration? 20 30 35 40 45 Number 25.0 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)? base to the solution unti ijust turns pink. You may need to reset the titration if Number you go past the end point. 148 g/ mol Since molar mass has units of grams per mole can calculate the molar mass of a sample by dividing s mass in grams by the number of moles in that sample The number of moles of diprotic acid in the flask is half the number of moles of NaOH you need to add to reach the equivalence point.Explanation / Answer
ANSWER
Since first part is correct , here we attempt 2nd part
At the end point the number of moles of acid = number of moles of base
Number of moles = Molarity X Volume
Moles of base required = 0.150 X 0.025 = 0.00375 moles, 25mL = 0.025L
Since the acid is diprotic the number of moles of acid required will be half of the number of moles of base
Therefore number of moles of acid = 0.00375 / 2 = 0.001875 moles
No. of moles = Mass in grams / Molar mass
Molar mass = mass in grams / No. of moles
Molar mass = 0.556 / 0.001875 = 296.5 g/mole
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