Question

The boiling points of pure HF, HCl, HBr and HI are -20,-85, -66 and -34 degrees Celcius. Identify the trends in bond polarity and dispersion forces along this series.

i). Use the information to assess the relative strengths of these two effects in this case.

ii). Suggest a reason for the anomalous behaviour of HF.

Calculate the total number of atoms in a 3.2cm^3 sample of pure liquid HCl, the number of moles of HCl in 1L of the pure liquid. Note that the density of liquid HCl is 1.49 g cm^-3

Answer 1

Answer in Bend polasity Trends H-F 7 H-4HI Br H-T Jeast pola Most polay HIF Bond is most polat while the H-I bond is Least polay In HF hydhogen bonding is poesi ble van duiwall force While in the rest there 1 aHe Fluorine i HF because a no malous be havi owy shouo Halogens Laast most electron ègative amon ydegen bonding is posible only HF. Thus HF has highest boiling boint. So 3-2 Cm3 of puHe liqud H 1-49 &/Cm3 Total no. of atom in dungity of liqud H Cm3 liq HCI 3-2 Cm3 liq H =1.49 moles of HC 1 36-5 = 0.1306 mole X 6.02 3 X Lo23 no of mole culifH= in 3.2 CmHu O1306 molecules 0.7867 X lo23 no of atoms in Imolecule of Hu - 2 3-2 Cm3 of HCI no ot atoms in 2 X0-7867 X lo23 23 1.573 X Lo molecule

liqui'd pwie i) Number of moles of Hu in 11of the dinsity of liquid H = 1-49 g/Cm3 1 (m3 of liquid HI1-49 l000 Cm of liquid Hu= 1.49 XL000 Litre = Loo0 (m3 of HC moles of HI M 36.5 moles of HLl= 40.82 mol es