Module 3: BOILING POINT AND MELTING POINT OF ORGANIC COMPOUNDS

Boiling and Melting Points * physical properties that can help: ✓__________ unknown compounds ✓functions as an ___________ of substances

BOILING POINT • the temperature at which the ____________ of the substance is ___________ to the _______________ above it

BOILING POINT • the boiling point of a liquid varies with the atmospheric pressure: • it is also an indicator of the volatility of the compound:

BOILING POINT : a liquid at a higher pressure has a higher boiling point than a liquid at a lower atmospheric pressure (varies) (True or False)

BOILING POINT : the lower the boiling point, the more highly volatile the substance is, and vice versa (volatility) (True or False)

• other factors may also affect the boiling point:

• at a given temperature, a compound will exist as: ✓ “gas” if it has a _________________________ ✓ “liquid or solid” if it has _________________

Intermolecular forces of attraction • it occurs between ________________________, “influences” __________ the boiling point and are dependent on the __________________ present on the organic compound

• “weak” intermolecular attraction formed by "induced polarization”\ of molecules which is caused by fluctuating charges due to the nearness of the molecules as they vibrate

• the intermolecular forces go in the order

• the functional groups which most easily ionize are “amines and carboxylic acids”, such as the reaction of ammonia (NH3) with a carboxylic acid (carboxylate ion)

• boiling point increases as the number of _______________ ✓due to more energy that is required to overcome the increased forces of attraction caused by long carbon chains

• commonly observed among [ “hydrocarbon groups” ] and occurs only within [ “short distances” ] in between molecules

• these molecules contain an [ “asymmetrical charge” ] due to the two poles of the molecule: one end is partially negative while the other end is partially positive

• occurs among [ “partially ionic or polar molecules” ]

• formed between [ “partially positive hydrogen (H+)” ] and an [ “adjacent electronegative atom” ] which bears a partial negative charge

• intermolecular ______________ tend to “rise boiling point” of an organic compound

• takes place between molecules having “opposite charges” and involves an “electrostatic interaction” between the two opposite charges

• another factor that can affect boiling point is the

• boiling point increase in the presence of ________________ impurities ✓due to decrease in the vapour pressure of the liquid

• boiling point decrease in the presence of __________ ✓it causes the surface area of the molecules to decrease thereby decreasing the forces of attraction between individual molecules

• boiling point increase as the polarity of the substance ________________ ✓due to the attraction of the positive end of one molecule to the negative end of another molecule

• boiling point ____________ in the presence of volatile impurities ✓due to the increase in the vapour pressure of the liquid

• the temperature at which a solid compound is directly converted to its liquid state