Jane Chemist was trying to analyze the mass percent of formic acid in an unknown

Question

Jane Chemist was trying to analyze the mass percent of formic acid in an unknown aqueous solution. Formic acid has the formula HCOOH and reacts with sodium hydroxide according to the balanced chemical equation shown below. If 15.00 mL of the unknown solution (density = 1.00 g/mL) were titrated with 0.1070 M NaOH solution and it took 21.04 mL of the NaOH solution to reach the endpoint of the titration, what was the mass percent of formic acid in the original unknown solution? Discuss the purpose of the buret in a titration. How does its design help the user accomplish this purpose?

Explanation / Answer

1) Given,

Volume of unknown solution = 15 mL

Molarity of NaOH solution = 0.107 M

Volume of NaOH solution = 21.04 mL

=> Millimoles of NaOH added = 0.107 x 21.04 = 2.25

At end point,

Moles of Acid added = Moles of Base added

=> Millimoles of HCOOH in solution = 2.25

=> Molarity of HCOOH solution = 2.25 / 15 = 0.15 M

=> There are 0.15 moles of HCOOH per 1000 mL of unknown solution.

Given, density of unknown solution = 1 g /mL

=> There are 0.15 moles of HCOOH per 1000 g of unknown solution.

Molar Mass of HCOOH = 46 g / mol

=> There are 0.15 x 46 = 6.9 g HCOOH in 1000 g of solution

=> Mass % of HCOOH = 6.9 x 100 / 1000 = 0.69 %

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