Boiling point of compound

Figure 5.12 Melting and boiling points of compounds with substitution groups (a) methyl compounds (b) ethyl compounds...

Table 12.2 Comparison of the Effect of Functional Groups on Melting and Boiling Points of Compounds of Comparable Molecular Mass...

Steam distillation is used when normal distillation is not an option, due to thermal sensitivities. By adding water or steam, the boiling points of compounds can be depressed, allowing them to evaporate at lower temperatures. After distillation the vapours are condensed and typically yield two phases water and organics. These can then be easily separated on the basis of their different densities. On a simple level, this can be seen every day in fresh black coffee, where small amounts of organic, water-immiscible oils float on the surface. Steam distillation is employed on an industrial scale in the manufacture of essential oils (e.g. lavender, eucalyptus and fruit oils) that are used in the food and flavour industries. In this area, the use of water is highly desirable as a natural solvent. Steam distillation is also used in petroleum refineries and petrochemical plants, where it is commonly referred to as steam stripping . 

Understand the role that molecular geometry plays in determining the solubility and melting and boiling points of compounds. 

Researchers often find different melting points and boiling points for the same compound, depending on the reference book they use. The reason for this discrepancy is that many scientists have measured the melting points and boiling points of compounds. Those scientists do not always get the same result. So, it is difficult to know what the true or most correct value is for these properties. In this book, the melting points and boiling points stated are taken from the Handbook of ChemiAtry and PhyAicA. 

Distillation is a purification technique that involves using the different boiling points of compounds to effect their separation. As a solution containing a mixture of chemicals is heated the compound with the lowest boiling point will evaporate first, and this can be collected on a cool surface after it has diffused away from the solution. In this way, a pure liquid component can be isolated from a mixture of liquids. 

When boiling points of compounds with similar molecular weights are compared, the carboxylic acids have the highest boiling points of any organic compounds we have studied so far (see h Table 5.3 and h Figure 5.4). 

Boiling Points of Compounds with Similar Molecular Weight... 

An increase in the number of polar functional groups in the molecules leads to an increase in the strength of inter-molecular interactions. This is manifested as a rise in melting and boiling points of compounds. For example, some aliphatic diols and triols have boiling points at atmospheric pressure and, hence, are volatile enough for GC analysis. Similar compounds with four or more hydroxyl groups have... 

When comparing boiling points of compounds, we look for the following factors ... 

For a molecule to escape these same attractive forces in the liquid state and enter the gas phase, more heat has to be applied. When the vapor pressure of a liquid equals atmospheric pressure, boiling occurs. Boiling points of compounds are also relatively high if the intermolecular forces are relatively large. These effects lead to the smooth increase in boiling points seen in Figure 2-5. 

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