Question

4. Calculate the mole fraction of phosphoric acid (H3PO4) in a 25.4% (by mass) aqueous solution. (Assume 500 mL of solution.) Please show work

Answer #1

**1)**

**consider 500 ml of solution**

**assuming the density of solution as 1 g /
ml**

**now**

**mass = density x volume**

**so**

**mass of soltuion = 1 x 500**

**mass of solution = 500 g**

**now**

**we know that**

**% mass = mass of H3P04 x 100 / mass of
solution**

**so**

**25.4 = mass of H3P04 x 100 / 500**

**mass of H3P04 = 127**

**now**

**we know that**

**moles = mass / molar mass**

**so**

**moles of H3P04 = 127 / 98 = 1.296**

**now**

**mass of water = 500 - 127 = 373**

**so**

**moles of water = 373 /18 = 20.722**

**now**

**total moles = 1.296 + 20.722 =22.018**

**now**

**mole fraction of H3P04 = moles of H3P04 / total
moles**

**so**

**mole fraction of H3P04 = 1.296 / 22.018**

**mole fraction of H3P04 = 0.059**

**so**

**the mole fraction of H3P04 is 0.059**

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