At 300 K and 1.00 atm, density of gaseous HF is 3.17 gL-l. How many HF molecules are associated by H-bonding?

p=nVRT=wmVRT Since wV=gL−1= density Hence p=dmRTm (HF-associated) =dRTp=3.17×0.0821×3001.00=78.08gL−1m (HF) of single unit =20gL−1Thus, number of HF molecules = 78/20 ≈ 4