A chemistry student needs to standardize a fresh solution of sodium hydroxide. She carefully weighs out 356.mg of oxalic acid H2C2O4, a diprotic acid that can be purchased inexpensively in high purity, and dissolves it in 250.mL of distilled water. The student then titrates the oxalic acid solution with her sodium hydroxide solution. When the titration reaches the equivalence point, the student finds she has used 115.4mL of sodium hydroxide solution.Calculate the molarity of the student's sodium hydroxide solution. Round your answer to 3 significant digits.
Question
A chemistry student needs to standardize a fresh solution of sodium hydroxide. She carefully weighs out 356.mg of oxalic acid H2C2O4, a diprotic acid that can be purchased inexpensively in high purity, and dissolves it in 250.mL of distilled water. The student then titrates the oxalic acid solution with her sodium hydroxide solution. When the titration reaches the equivalence point, the student finds she has used 115.4mL of sodium hydroxide solution.Calculate the molarity of the student's sodium hydroxide solution. Round your answer to 3 significant digits.
Solution
To calculate the molarity of the sodium hydroxide solution, we need to follow these steps:
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Convert the mass of oxalic acid to moles. The molar mass of oxalic acid (H2C2O4) is approximately 90.03 g/mol. So, 356 mg is equal to 0.356 g. Therefore, the number of moles of oxalic acid is 0.356 g / 90.03 g/mol = 0.00395 mol.
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Since oxalic acid is a diprotic acid, it can donate two protons. Therefore, the moles of sodium hydroxide (NaOH) needed is twice the moles of oxalic acid, which is 0.00395 mol * 2 = 0.00790 mol.
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The volume of the sodium hydroxide solution used is 115.4 mL, which is equal to 0.1154 L.
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The molarity (M) of a solution is defined as the number of moles of solute (NaOH in this case) divided by the volume of the solution (in liters). Therefore, the molarity of the sodium hydroxide solution is 0.00790 mol / 0.1154 L = 0.0684 M.
So, the molarity of the student's sodium hydroxide solution is approximately 0.068 M, rounded to three significant digits.
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