Pls ans the questions mL Reset The flask shown here contains 0.410 g of acid and

Question

Pls ans the questions mL Reset The flask shown here contains 0.410 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.100 M NaOH 5 10. What volume of base is needed to reach the end point of the titration? 20 25 30 35 40 45 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)? Add base to the solution unti it just turns pink. You may need to reset the titration if you go past the end point. Number g mol

Explanation / Answer

I think that the volume used of base is 10,5mL, but it depends of the eye (so, the answer to the first question is 10,5mL). Let´s do the calculations with that number.

mol of NaOH= 0.1M x 10.5x10-3L = 1.05x10-3mol= mol of acid

molar mass= 0.41g/ 1.05x10-3mol= 390.5g/mol

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pH= pKa + log[A-]/[HA]

[A-]= concentration of conjugated base of the acid HA.

5.875= 5.636 + log [succinate]/0.0503M

0.239= log [succinate] - log0.0503

[succinate]= 0.0872M ---> mol= 0.0872M x 0.590L= 0.051448 mol ---> mass= 0.051448 mol x 248.32g/mol= 12.8g

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