4/9/2018 08:00 AM O 733/ 100 Gradebook Print CalculatorPeriadic Table Question 1

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4/9/2018 08:00 AM O 733/ 100 Gradebook Print CalculatorPeriadic Table Question 12 of 15 Sapling Learning The flask shown here contains 0.386 g of acid and a few drops contains 6.120 M NaOH ndicator dissolved in water. The buret 10 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)? Add base to the solution unti it just turns pink. You may need to reset the btration you go past the end point Number g/mol arch ??????????????????????sssssssss V V ?????? ??????? )???? ,? '????????????????????? ?????????

Explanation / Answer

From the figure, the volume of base consumed to reach the end point is 15 mL.

Since acid is diprotic, the mole ratio of acid and NaOH is 1:2.

Moles of NaOH = molarity of NaOH x volume of NaOH = 0.120 M x 15 mL = 0.120 M x 0.015 L = 0.0018 mol

Moles of Acid = 0.0018 mol NaOH x ( 1 mol Acid/ 2 mol NaOH) = 0.000900 mol

Molar mass of Acid = mass of acid/moles of acid = 0.386 g/0.00090 mol = 429 g/mol.

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