1) Two substances obtained from different sources each melt at148 - 150 degrees
ID: 889783 • Letter: 1
Question
1) Two substances obtained from different sources each melt at148 - 150 degrees celsius . Are they the same ? explain
2) Benzoic acid and 2 naphthol each melt at 122 degrees celsius. A sample of unknown solid melts around 122 degrees celsius. Thesolid is either benzoic acid or 2- naphthol . Describe a method todetermine the identity of the unknown compound.
3) Explain why atmospheric pressure affects boiling points of liquids, but does not affect melting points of solid.
4) Do impurities always lower melting point of an organic point? Explain
Explanation / Answer
(1)
If they are not the same compound they will be veryclose.
They could be isomers of each other.
For example CCCCC (normalpentane) will have higher than CCCC 2 pentane. The moresurface area you have the higher the boiling point,with the 2 pentane there is a branch off the second carbonwhich has less surface area than the straight chain pentane sothe boiling point will be lower. So they could be thesame number of element but justbonded differently.
(2) You could do an extraction with an organic base. You would dissolve your unknown in an organic solvent, and then add the base. You would then do an extraction with water. If your compound turns up in the water, it was benzoic acid, because itreacted with the base. If it remains in the organic solvent,it was 2-naphthol.
(3) When a liquid boils, the particles in the liquid overcome intermolecular forces of attraction and escape into the vapor phase. If the pressure of that vapor phase is increased, the particles need more kinetic energy to escape because they must overcome the extra forces pushing them into the liquid phase.
When a solid melts, particles in the liquid phase aren't escaping , So the vapor pressure doesn't really change that process.
(4) yes impurities lower melting point of compounds. Impurities atoms enters lattice sites of compound and disturb lattice structure. Thus lattice energy of crystal decreases and hence melting point decreases.
Impurities decrease the intermolecular attractions of the compound , thereby decreases melting point of the compound.
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