Answer i) The hydroxyl group of alcohol makes the hydrogen bond with water molec

Question

Answer i) The hydroxyl group of alcohol makes the hydrogen bond with water molecules while corresponding alkanes do not make hydrogen bonding with water. Therefore, surface tension of alcohols are greater than corresponding alkanes.

Answer ii) As the length of hydrocarbon chain in alcohol incerease, more energy will be needed to overcome the hydrogen bonds between the alcohol molecules as the molecules are more tightly packed together as the size and mass increases. Therefore, surface tension and interfacial tension of n-hexanol are lower than that of n-octanol.

Answer iii) n-Hexanol and n-octanol will not spread on water because these can make hydrogen bonding with water molecules and are soluble in water because of high surface tension as compared to corresponding alkanes.

Explanation / Answer

(c) The surface and interfacial tension values against water at 25 °C have been measured for the compounds listed below: | Substance Yo[mN m-lj Yi{mN m-11 H;0 72.6 n-Hexane (C6H14] 18.8 n-Hexanol (C6H13OH] 25.2 5.9 n-Octane (C8H18). 21.9 50.8 n-Octanol (C8H11OH] 27.5 8.5 50.9 Account briefly for the following observations: (i) The surface tensions of the alcohols are greater than the surface tension of the corresponding alkanes. (ii) The surface and interfacial tensions of n-hexanol are lower than those of n-octanol. (iii) Of the four organic compounds above which will not spread on water? Why?

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