An unknown sample is analyzed using paper chromatography using solvent X as mobile phase. One spot is observed after the paper is developed. The same unknown substance is re-analyzed using solvent Y as the mobile phase. This time, three spots are observed after the paper is visualized. Is the unknown sample a pure substance or a mixture? Explain your answer.

The substance is a mixture

Explanation:

The question lets us know that when solvent X was used as the mobile phase, we obtained only one spot. This may deceive us into thinking that the substance is pure since a pure substance has only one spot on a chromatogram.

However, the same substance yields three spots with solvent Y. This shows that the unknown sample is a mixture of substances and solvent X was unable to fully separate the mixture.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"

water and alcohols have similar properties because water molecules contain hydroxyl groups that can form hydrogen bonds with other water molecules and with alcohol molecules, and likewise alcohol molecules can form hydrogen bonds with other alcohol molecules as well as with water.