An analytical chemist weighs out 0.101g of an unknown triprotic acid into a 250mL volumetric flask and dilutes to the mark with distilled water. He then titrates this solution with 0.1700M NaOH solution. When the titration reaches the equivalence point, the chemist finds he has added 18.2mL of NaOH solution.Calculate the molar mass of the unknown acid. Round your answer to 3 significant digits.
Question
An analytical chemist weighs out 0.101g of an unknown triprotic acid into a 250mL volumetric flask and dilutes to the mark with distilled water. He then titrates this solution with 0.1700M NaOH solution. When the titration reaches the equivalence point, the chemist finds he has added 18.2mL of NaOH solution.Calculate the molar mass of the unknown acid. Round your answer to 3 significant digits.
Solution
To calculate the molar mass of the unknown triprotic acid, we need to follow these steps:
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Calculate the moles of NaOH used in the titration. The formula for this is Molarity (M) = moles/Liter. So, moles of NaOH = Molarity * Volume(L). The volume of NaOH used is 18.2 mL, which is 0.0182 L. Therefore, moles of NaOH = 0.1700 M * 0.0182 L = 0.003094 moles.
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Since the acid is triprotic, it means that each mole of acid reacts with three moles of NaOH. Therefore, the moles of the unknown acid = moles of NaOH / 3 = 0.003094 moles / 3 = 0.001031 moles.
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The molar mass of the unknown acid is the mass of the acid divided by the moles of the acid. The mass of the acid is given as 0.101 g. Therefore, the molar mass = 0.101 g / 0.001031 moles = 97.96 g/mol.
So, the molar mass of the unknown acid is approximately 98.0 g/mol when rounded to three significant digits.
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