Acetic acid, CH3COOH, forms stable pairs of molecules held together by two hydro

Question

Acetic acid, CH3COOH, forms stable pairs of molecules held together by two hydrogen bonds. Such molecules—themselves formed by the association of two simpler molecules—are called dimers. The vapor over liquid acetic acid consists of a mixture of monomers (single acetic acid molecules) and dimers. At 100.6°C, the total pressure of vapor over liquid acetic acid is 436 mmHg. If the vapor consists of 0.638 mole fraction of the dimer, what are the masses of monomer and dimer in 1.000 L of the vapor? What is the density of the vapor?

Mass of monomer = ____ g monomer

Mass dimer = _____ g dimer

Density = ____ g/L vapor

Explanation / Answer

now

we know that

PV = nRT

so

( 436/760) x 1 = n x 0.0821 x 373.6

n = 0.0187

so

total moles = 0.0187

now

mole fraction of dimer = moles of dimer / total moles

so

0.638 = moles of dimer / 0.0187

moles of dimer = 0.0119306

now

mass of dimer = moles x molar mass

mass of dimer = 0.0119306 x 120

mass of dimer = 1.43 grams

now

moles of monomer = 0.362 x 0.0187

moles of monomer = 6.7694 x 10-3

mass of monomoer = 6.7694 x 10-3 x 60

mass of monomer = 0.406 grams

now

PM = dRT

d = PM / RT

now

average molar mass = ( 0.638 x 120 ) + ( 0.362 x 60)

average molar mass = 98.28

so

d = ( 436/760) x 98.28 / 0.0821 x 373.6

d = 1.838

so

the density of vapor is 1.838 g / L

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects