Calculate the mole fraction of HCOOH in an aqueous solution containing35.5%by mass of HCOOH?

Question

Mhcooh= 46g/mol Mh2o=18g/mol

Answer 1

By definition, a 35.5% by mass solution of HCOOH contains 35.5 g of HCOOH in 100 g of solution.

If we have 100 g of solution, and 35.5 g is HCOOH, then the remainder must be H2O.

Grams H2O = 100 g - 35.5 g = 64.5 g

So, we have 64.5 g H2O and 35.5 g HCOOH

To get mole fraction, we needs to convert grams to moles and then take the ratio of mole HCOOH to total moles.

moles HCOOH = 35.5 g HCOOH x 1 mol/46 g = 0.772 moles

moles H2O = 64.5 g H2O x 1 mol / 18 g = 3.58 moles

Total moles = 0.772 + 3.58 = 4.36 moles total

Mole fraction HCOOH = 0.772 mol / 4.36 mol = 0.177