Use the information and data given below to answer the questions (a) to (c):

• Stronger intermolecular forces result in higher boiling point.

• Strength of London forces increases with the number of electrons in the molecule.

• Boiling point of HF, HCl, HBr and HI are 293 K, 189 K, 206 K and 238 K respectively.

 

(a) Which type of intermolecular forces are present in the molecules HF, HCl, HBr and HI?

(b) Looking at the trend of boiling points of HCl, HBr and HI, explain out of dipole-dipole interaction and London interaction, which one is predominant here

(c) Why is boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?

<p><span data-teams="true">This is a short answer type question as classified in NCERT Exemplar</span></p><p><strong> (a)&nbsp;</strong>HCl, HBr and HI have dipole-dipole and london dispersion&nbsp; interaction &nbsp; whereas HF has hydrogen bonding in addition (due to the high electronegativity of the F atom).</p><p><strong> (b) </strong>The electronegativity decreases from Cl, Br and I so the dipole-dipole interaction will also decrease as HCl &gt; HBr &gt; HI&nbsp; and it is contrary to the boiling point order which is HCl &lt; HBr &lt; HI. This confirms that the London interaction is predominant.</p><p><strong> (c) </strong>F atom has the highest electronegativity so it has hydrogen bonding interaction in addition to &nbsp; dipole-dipole and london dispersion&nbsp; interaction which leads to the highest boiling point of HF whereas&nbsp; HCl has the lowest boiling point&nbsp; because london force plays&nbsp; the predominant role in boiling point than dipole-dipole interaction and&nbsp; london force increases proportionally with the molecular weight of the compound. HCl has the lowest molecular weight among HCl, HBr and HI therefore it has the least london force interaction which leads to the lowest boiling point</p>

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